++++ start of p. *18 in SOO 8 ++++ **********************************************************************
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3-A. Methods of Observation---------------------------------- 18
3-B. Shortcomings ------------------------------------------- 18
3-C. Tolerable Observation Effort (TOE)---------------------- 20
3-D. Figure and Tables--------------------------------------- 21
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Most observations were around the buildings near the House in the SW corner of the Study Area (Fig. 2.1). Observations were made while Faxon worked out of doors and often averaged about 8 hours/day until about 1986 (when injuries and other commitments often resulted in shorter daily observations).
It is important to note that Faxon's observations were made incidentally to his other activities and duties; Faxon did not attempt to do systematic surveys of all birds present in the Study Area.
Binoculars were always used for observations during spring and fall bird migration and near the house; otherwise, binoculars were not always feasible.
Faxon made his observations while engaged in various activities around the Faxon Farm. Many of his activities were outside, where he could notice birds. For example, Faxon wrote about his 1973-1986 activities:
"Every morning from somewhere around 6 to 7:30 AM I milk the cow and do
some chores around the barn, or, in the summer, perhaps work in the
garden. Following breakfast, I am back outside from shortly after
8 AM until around 12:30 PM. My work is quite varied, but practically
all of it is outside, or at least partly so. That is, even if I am
working inside the barn, I am only a step or two from being completely
outside. Much of the time in the summer I spend logging with horses,
so noise from machinery is not a problem, in terms of not being able
to hear birds around me."
"Other jobs include moving cattle around, fixing fence, clearing land
and so forth. In the winter time I spend a lot of time planting,
bud-capping, and clearing brush around Douglas-fir seedlings. Also,
usually two or three days a week I pick sword fern to sell. My
afternoon schedule is much the same as the morning, causing me to be
outside from 1:30-6 PM most days."
Since February 1986, injuries have hampered Faxon's activities, so he has not been able to be outdoors as much as in previous years. Further, beginning in February 1988, he has spent at least one weekday each week away from the Farm doing pastoral work as a minister. Thus, since about February 1986, Faxon has not spent as much time and effort birding here as previously.
Newspaper articles about Faxon's and his father Milt's horse logging (which is unusual in this area), or Faxon's birding are in Mavity (1977), Bragg (1989a,b), and Viall (1989).
From April 1973 through December 1990, the average number of observation days per month ranged between 19 and 24 days with only nine months having less than 10 observation days (Table 3.1). The only months with no observations during this period were in July 1983 (when one of Faxon's horses kicked him and sidelined him the whole month) and July and November 1986 (Table 3.1).
The dates when Faxon made no observations or recorded five or less bird species are given in Table 3.2.
During the first few days of the month, Faxon wrote his bird observations on graph paper as he made them. Later in the month, species that were observed or heard each day were checked off on the sheet of graph paper at lunch and/or at the end of the day.
Bayer compiled these records from Faxon's written observations, from Faxon's field note columns in the "Sandpiper" (which is the newsletter of Yaquina Birders and Naturalists) from September 1985 through 1990, and from correspondence with Faxon.
The main body of these observations are based on Faxon's April 1973-1990 observations. Prior to April 1973, Faxon made some incidental observations, which are included in this compilation as incidental notes for individual species. Faxon continued his observations in 1991, but only notes of particular interest about individual species are included in this Volume.
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In ornithological undertakings there are usually shortcomings, and "The Birds of Thornton Creek" is no exception. The shortcomings are included here, so that readers can better interpret, understand, and learn from this compilation.
Because of changing outdoor chores, Faxon did not cover exactly the same areas each day. Some activities such as summer haying would result in Faxon being at some areas that he would not be at in other seasons. Further, Faxon's activities at an area could change seasonally; for example, in coniferous forests, Faxon picked fern or planted trees in winter, but, in summer, he often was logging and using a chain saw. Nevertheless, some areas, such as around the house and barns were usually birded daily throughout the year.
++++ start of p. *19 in SOO 8 +++++++++++++++++++++++++++++++
Another shortcoming is that Faxon's observation effort was somewhat variable. Although observation effort was not directly quantified, indices of observation effort include the number of observation days each month (Table 3.1), the number of bird species seen each day (Table 3.3), and the number of bird species found each month (Table 3.4).
DAILY VARIATION.--One indication of variable observation effort is that there was often a wide range in the number of species seen daily during a month (Table 3.3). Although some of this variation could be attributed to changes in bird presence among days, it is likely that much of the variation is a result of changing observation effort because of variability in Faxon's activities and in the time available during a day to note birds.
MONTHLY VARIATION.--Other evidence that observation effort fluctuated is that the number of observation days/month (Table 3.1) and the number of species/month (Table 3.4) differed among years for the same month.
In fact, there appears to be some patterns to the changes in observation effort among years (Fig. 3.1). For example, in 1973-1975, Faxon was just beginning to take systematic notes, was learning to identify some birds that he hadn't previously known, and was learning to identify more birds by call alone. Thus, it is not surprising that in these years, Faxon typically had more months in which he noted as great or greater than average number of observation days, but fewer months with at least an average number of species (Fig. 3.1). 1976 was a transition year.
In 1977-1979, a more experienced Faxon had more months with an above average number of observation days and species, but, after a transition year in 1980, his effort appeared to have dropped in 1981-1984 with usually few months having an average number of observation days and species (Fig. 3.1).
1985 was another transition year, and the 1986-1988 pattern was a reversal of the 1973-1975 pattern with fewer months with at least an average number of observation days, while more months had at least an average number of species (Fig. 3.1). The reversal between 1973-1975 and 1986-1988 probably resulted because Faxon's skills and efficiency as an observer had improved and thus offset the reduced number of observations in 1986-1988.
Similarly to 1981-1983, the number of months with at least an average number of observation days and species was low in 1989 and 1990 (Fig. 3.1).
RELATIONSHIP BETWEEN DAILY AND MONTHLY VARIATION.--An examination of Fig. 3.1 makes it appear that the number of Faxon's observation days/month might often be unrelated to the number of species/month; this was confirmed statistically. Only in the June-August period was there a significant relationship between the number of observation days and the number of species/month (Table 3.5).
The average number of species/day was inversely related to the number of observation days/month (i.e., with increasing numbers of observation days, the average number of species/day decreased)(Table 3.5). This relationship was significant in most periods within a year, but not in May (Table 3.5).
The number of species/day and species/month were significantly correlated for all intervals during the year (Table 3.5). Thus, if Faxon spent a lot of effort each day and recorded more than the average number of species, he was also more likely to record more species that month.
SEASONAL VARIATION.--Faxon's observation effort also appeared to vary somewhat seasonally. Because of more daylight, Faxon could observe longer during summer days than during winter days. Further, the average number of observation days was greater in April-May and July-August than throughout the rest of the year (Table 3.1), so it appears that Faxon's coverage might have been more comprehensive in spring and summer than in fall and winter.
The presence of a few species was consistently missed. This applies mainly to Hammond's Flycatchers before 1977 and to owls. Hammond's Flycatchers were overlooked before 1977 because Faxon had not yet learned their call. Owls were not regularly observed because Faxon was not actively birding in the evening.
In some months in recent years, Faxon failed to record some common species that were probably present. Some of these species include European Starling, Steller's Jay, Dark-eyed Junco, and Northern Flicker. These lapses in documentation should not be construed as these species being absent. Rather they indicate that Faxon's effort may have sometimes emphasized and been selective for rarities, instead of common species.
Variability in areas censused (section 3-B-2) and in observation effort (section 3-B-3) could also have resulted in some species being overlooked or missed that were actually present.
It is unfortunate that Faxon did not have a good camera and telephoto lens or a collecting permit to document the rare birds that he has seen at Thornton Creek. Since he saw many of these rarities during migration when they were present only for short periods of time and other birders were generally unavailable to come to Thornton Creek, he was unable to have other observers confirm these rarities.
When one compares Faxon's rarities with some of those found at the Farallon Islands near San Francisco (e.g., DeSante and Ainley 1980), one is struck by many of the similarities. This is not to say that work at the Farallones confirms Faxon's sightings, but it indicates that intensive field work results in the discovery of birds that are not expected to be present.
++++ start of p. *20 in SOO 8 +++++++++++++++++++++++++++++++
Faxon also did not record the abundance of each species. However, censusing terrestrial birds is difficult at best (e.g., see Ralph and Scott 1980, Verner 1985), and it simply was not feasible for Faxon to do so at Thornton Creek. Thus, frequencies given here refer to the frequency of occurrence and not to abundance. The problem with this is that a species represented by a lone individual could have a higher frequency per month than a species that is represented by 50 or more individuals.
It would have been much more informative if Faxon had separated his daily bird records for each habitat (e.g., creek, riparian, pond, field, brush, coniferous forest, and deciduous forest) or site (e.g., records just for Pond C or just for the field west of the Faxon house). Such records could also be used to predict what birds may be present at similar habitats or sites.
Although he may not have birded some habitats or sites very often (e.g., about once a month for Pond D), these records might still have been adequate to point out differences in bird distribution or seasonality compared to sites such as Pond C that were birded nearly every day.
While it is unfortunate that Faxon did not separate records for each habitat or site, the exponentially increased record keeping that would have resulted from doing so would probably have discouraged Faxon from making 18 years of records. ******************************************************************************
The term Tolerable Observation Effort (TOE) is used to emphasize that if certain criteria of observation effort are attained, effort is judged Tolerable (i.e., moderately good or passable), and observations are considered as presence/absence data, not just presence data. However, TOE does not indicate an effort in which all species present were recorded; TOE suggests only that effort was probably sufficient to find most, if not all, conspicuous or common species and, perhaps, some of the more inconspicuous or uncommon species.
A TOE month is one:
1) with three or more systematic censuses per month by an experienced
observer, no matter how many species were recorded;
or 2) when the number of recorded species was 60% or more of the maximum for
three or more years for that month (i.e., 60% MAX) and there were at
least five species recorded.
At Thornton Creek, all months with any observations at all qualified as TOE months by criteria #2, and there were 16-18 TOE months for each calendar month (Table 3.4). TOE months were used in calculating average relative monthly frequencies of occurrence during the 1973-1981 or 1982-1990 periods (section 1-D). TOE months included all those in which daily frequencies were calculated as well as three additional months in which daily frequencies were not calculated because there were less than eight observation days (Tables 3.1 and 3.4).
++++ start of p. *21 in SOO 8 +++++++++++++++++++++++++++++++ **********************************************************************
FIGURE 3.1. Percentage of months each year whose observation days/month (X) or bird species/month (Y) was greater than or equal to the 1973-1990 monthly average at Thornton Creek. Only months with more than five days of observation are included, and the number of these months each year is given along the baseline.
These data were compiled from data in Tables 3.1 and 3.4. Months with greater than or equal to the average were determined from averages calculated to the nearest 0.1, not averages rounded off to the nearest whole number as given in Tables 3.1 and 3.4.
++++ Lines connecting points were hand-drawn in the printed version. ++++
Percentage of Months Greater than or Equal to the 1973-1990 Monthly Average
Days/Month (X)
100-| X XY
|
P | X X X Y
e | X
r | Y X X X
c 80-|
e |
n |
t | Y
a |
g 60-| Y
e | 50% 50% Y
| ------------Y---------------Y---------------X-------Y----------------
o |
f | Y X Y Y
40-|
M | X
o | Y Y X Y
n |
t | X Y X
h 20-| X
s | Y Y X
|Species/Month (Y)
| Days/Month (X)
|
0-| X
|
| 9 12 12 12 12 12 12 12 12 12 11 12 12 10 12 12 12 11
|______________________________________________________________________
| | | | | | | | | | | | | | | | | |
1974 1976 1978 1980 1982 1984 1986 1988 1990
++++ start of p. *22 in SOO 8 +++++++++++++++++++++++++++++++
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TABLE 3.1. Number of observation days per month at Thornton Creek in 1973-1990. Only days with six or more species/day are included; days with little or no observation effort (i.e., five or less species/day) are listed in Table 3.2.
For years with at least one observation day: N=number of non-zero years, AV=monthly average, SD=Standard Deviation, MIN=monthly minimum, MAX=monthly maximum.
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Observation Days/Month........................
Yr Ja Fe Mr Ap My Jn Jl Ag Sp Oc Nv De
--------------------------------------------------
73 0 0 0 30 28 30 30 31 26 19 26 30
74 26 26 28 29 31 27 26 24 25 25 19 25
75 21 26 28 26 29 27 29 28 24 29 25 27
76 28 27 31 29 25 27 26 26 26 26 25 28
77 28 25 27 30 29 23 28 29 26 25 25 22
78 21 19 23 26 26 24 28 26 24 25 25 26
79 28 23 22 27 27 20 26 23 23 23 22 19
80 22 24 24 24 24 21 23 16 24 21 22 17
81 21 22 21 24 21 21 24 19 19 19 13 13
82 23 18 18 22 26 20 17 22 9 20 24 14
83 20 21 24 26 23 20 0 21 16 13 16 21
84 26 24 27 17 20 24 17 27 16 27 20 14
85 24 19 29 27 27 21 28 26 25 22 15 20
86 18 14 5 23 26 13 0 21 20 17 0 8
87 10 16 18 23 23 21 21 28 22 29 25 17
88 18 21 22 18 19 17 14 24 17 17 8 10
89 13 15 14 16 15 13 15 22 21 14 20 19
90 19 17 21 10 13 13 16 16 5 12 0* 13
Summary for Months with at Least One Observation Day
N 17 17 17 18 18 18 16 18 18 18 16* 18
AV 22 21 22 24 24 21 23 24 20 21 21 19
SD 5 4 6 5 5 5 6 4 6 5 5 6
MIN 10 14 5 10 13 13 14 16 5 12 8 8
MAX 28 27 31 30 31 30 30 31 26 29 26 30
*=In November 1990, the number of observation days was not recorded but was
probably less than 10.
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TABLE 3.2. Days in which no observations were made or in which five or less bird species were recorded at Thornton Creek.
This Table can be used to determine if the First or Last date for a species may have been affected by a day with few or no observations.
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1973: Jan. (1-31), Feb. (1-28), March (1-31), May (11-13), July (3),
Sep. (8-9, 13-14), Oct. (18-29), Nov. (8, 23, 25, 27), Dec. (2)
1974: Jan. (6, 15, 20, 25, 27), Feb. (3, 10), March (3, 10, 24), April (9),
June (2, 16, 23), July (13-14, 23, 28, 31), Aug. (4, 11, 15-18, 23),
Sept. (5-8, 15), Oct. (6, 13, 18, 20, 26-27), Nov. (3, 10, 14-20, 23-24)
Dec. (8, 15, 17, 21-22, 29)
1975: Jan. (5, 7-8, 12, 19, 22-26), Feb. (15-16), March (1, 22-23),
April (12-13, 20, 27), May (4, 25), June (2, 8, 25), July (11, 13),
Aug. (2, 17, 30), Sept. (8, 17-20, 28), Oct. (12, 19),
Nov. (2, 13, 16, 23, 30), Dec. (7, 14-16)
1976: Jan. (3-4, 12), Feb. (1, 15), April (18), May (13-16, 25, 30),
June (8-9, 20), July (4, 18, 23-25), Aug. (7, 21, 28-29, 31),
Sept. (12, 17, 19, 21), Oct. (9, 17, 24, 27-28), Nov.(9, 14, 21, 23, 28)
Dec. (5, 12, 26)
1977: Jan. (2, 16, 23), Feb. (13, 20, 27), March (1, 6, 12, 27), May (20, 22)
June (12, 16-20, 25), July (5, 24, 30), Aug. (28-29),
Sept. (4, 11, 19-20), Oct.(4, 16, 20, 24, 29-30), Nov.(3, 6, 13, 16, 28)
Dec. (5, 10-11, 13, 15, 18, 20-21, 25)
1978: Jan. (2, 8, 10, 12, 15, 22, 25, 29-31), Feb. (5, 12, 14-17, 19, 26, 28)
March (5, 7, 9-12, 19, 26), April (5, 9-10, 30), May (5, 7, 14, 21, 28),
June (8-12, 24), July (4, 9, 16), Aug. (6, 11-12, 25, 30),
Sept. (3, 10, 15-17, 24), Oct. (1, 4, 9, 15, 22, 31),
Nov. (5, 12, 17, 19, 30), Dec. (3, 10, 12, 17, 24)
1979: Jan. (14, 21, 28), Feb. (4, 11, 18, 25-26),
March (4, 6, 18, 20-21, 25, 28, 30-31), April (12, 22, 29),
May (13, 20, 22, 27), June (3, 8-14, 17, 29), July (8, 15, 22, 27, 29),
Aug. (5, 11-12, 17, 19, 23, 26, 31), Sept. (2, 7, 15-17, 23, 30),
Oct. (7, 9-10, 13-14, 18, 21, 28), Nov. (4, 11, 14, 16, 18, 20, 25, 30)
Dec. (2, 5, 9, 12, 14-16, 18, 26, 29-31)
1980: Jan. (4-6, 12-13, 19-20, 25, 27), Feb. (10, 13-16),
March (9, 12, 16, 19, 26-27, 30), April (5, 13, 19-20, 23-24),
May (4-6, 11, 18, 25-26), June (6-10, 13, 15, 22, 29),
July (6, 10-13, 15, 20, 27), Aug. (2, 9-10, 16-18, 21-28, 31),
Sept. (7, 14, 18-19, 21, 28), Oct. (5, 7, 12, 14-15, 19, 24-26, 30),
Nov. (3, 6, 9, 16, 20, 23, 27, 29),
Dec. (3-4, 7, 9, 14, 16-17, 19, 21-22, 24-25, 28, 31)
Table 3.2 continued on next page
++++ start of p. *23 in SOO 8 +++++++++++++++++++++++++++++++
Table 3.2 continued
1981: Jan. (4, 11-12, 17-18, 20, 25, 29-31), Feb. (1, 3-4, 8, 14-15),
March (2-3, 7, 15-16, 22, 24-25, 29-30), April (4-5, 12, 19, 25-26),
May (3, 10, 17, 20-25, 31), June (5-8, 14, 19, 21, 28, 30),
July (4, 12, 19, 24-26, 31), Aug. (7-9, 12, 16, 23-26, 29-31),
Sept. (6, 11-14, 20, 24, 26-28, 30), Oct. (4, 11, 18, 20-25, 28-29, 31)
Nov. (4-5, 8-11, 14-16, 19, 21-24, 28-30),
Dec. (1-2, 4, 6, 8, 13-16, 20-27, 29)
1982: Jan. (2-3, 16-18, 21, 24, 31), Feb. (2, 6-7, 13-14, 18, 21, 26-28),
March (4, 7, 9-10, 14, 17, 19-23, 27-28),
April (4, 7, 11, 14, 17-18, 23, 25), May (9, 14, 16, 25, 30),
June (10-13, 19, 26-30), July (3-4, 9-11, 17-18, 22-25, 27, 29, 31),
Aug. (6-8, 10, 21-22, 24, 26, 29), Sept. (5-9, 11-12, 14, 18-30),
Oct. (5-8, 17, 19, 21, 24, 29-31), Nov. (7, 14, 20-21, 28, 30),
Dec. (2-5, 8, 11-12, 14-15, 19-23, 26-28)
1983: Jan. (4-6, 9, 15-16, 21, 23, 27, 29-30), Feb. (4-6, 25-28),
March (13, 19-20, 25, 27, 29-30), April(3, 24, 29-30), May(8, 16-20,31)
June (10, 12, 18-19, 23, 26-30), July (1-31),
Aug. (1, 4, 7, 14, 17-18, 21-22, 24, 28), Sep. (3-5, 9, 11-18, 21, 25),
Oct. (2, 9, 16-31), Nov. (6-7, 13, 15-17, 20-23, 27-30),
Dec. (5-8, 11-14, 18-19)
1984: Jan. (3, 8-9, 14, 31), Feb. (5, 9-11, 19), March (4, 11, 25, 28),
April (1, 3-11, 15, 22, 29), May (6, 13, 17, 20, 23, 25, 27-31),
June (2, 14, 17, 26, 29-30), July (1, 3-4, 9-10, 14-17, 19-22, 29),
Aug. (5, 12, 14, 26), Sep. (2, 8-9, 13, 16-23, 26, 30),
Oct. (7, 18-19, 21), Nov. (4, 10-11, 13, 18, 23, 25, 27, 29-30),
Dec.(6, 9, 12, 14-18, 22-27, 29-31)
1985: Jan. (2, 4-5, 7-8, 13, 27), Feb. (13-15, 19, 24-28), March (7, 17),
April (7, 12, 28), May (6-7, 12, 19), June (6-11, 16-17, 28),
July (7, 18, 20), Aug. (11, 17, 23, 25, 30), Sep. (1, 8, 21-22, 29),
Oct. (4-5, 10-15, 20), Nov. (3-15, 27, 29),
Dec.(6-10, 15, 21-22, 24, 28-29)
1986: Jan. (5, 8, 12-13, 15-16, 19-21, 26, 28-30), Feb. (4-5, 15-18, 21-28),
March (1-25, 30), April (9, 13, 16, 25-28), May (4, 18, 25, 27-28),
June (1, 7, 14-15, 18-30), July (1-31), Aug. (2-3, 7, 10, 17, 27-31),
Sept. (6-8, 10, 14, 17, 21, 26, 28-29), Oct. (5, 7-9, 12, 19-21,25-30)
Nov. (1-30), Dec. (1-12, 18-19, 21-22, 24-25, 27-31)
1987: Jan. (3-5, 10-24, 26-27, 31), Feb. (1, 3, 13-15, 17-23),
March (1-2, 4, 8, 15, 17-19, 22, 24-25, 28-29),
April (1-2, 11-12, 17, 19, 26), May (3, 17, 22, 24-26, 30-31),
June (5-6, 12, 14, 18, 21, 28-30), July (1-2, 12-13, 18-19, 22, 24-26),
Aug. (2, 12, 26), Sep. (5-6, 13, 21, 23, 25, 27-28), Oct. (4, 25),
Nov. (11, 13, 28-30), Dec. (3, 6, 8-10, 12-15, 20, 24, 27-29)
1988: Jan. (4, 10, 13, 17, 21-28, 31), Feb. (14-18, 20-21, 28),
March (6, 11, 13, 15, 18, 20, 22, 24, 27),
April (2, 4, 8, 10, 16-17, 22-24, 28-30),
May (1, 6-8, 13, 15, 20-22, 27, 29, 31), June (5, 9-13, 16-19, 24-26)
July (2-3, 8-12, 15-18, 22-23, 25-26, 30-31),
August (5, 14, 19-21, 26, 31), Sep. (2, 4, 9, 11, 15, 18, 21, 24-29),
Oct. (2, 7-9, 11, 20-21, 23-29), Nov. (3-10, 12-16, 18-25, 27),
Dec. (2, 4-6, 9-11, 13, 15, 17-21, 24-27, 29-31)
1989: Jan. (1, 5, 8-9, 12-13, 15, 19-20, 22-27, 29-31),
Feb. (10-12, 15-20, 23, 25-26, 28),
March (1, 3-5, 9-12, 14, 17, 20, 24, 26-29, 31),
April (2, 5, 9-11, 16, 19, 21, 23, 25-28, 30),
May (4, 7, 9-11, 13-14, 19, 21-23, 27-31),
June (4-5, 9, 13-23, 27, 29-30),
July (2-3, 7, 10-11, 14, 16-18, 21, 24, 27-31),
Aug. (4, 6-7, 11, 18-20, 25-26), Sep. (1, 7-9, 22, 24-27),
Oct.(1, 8, 11, 15-23, 25, 27-29, 31), Nov.(5, 12, 14, 19, 21, 25-28,30)
Dec. (1, 9-12, 16-17, 19, 26-27, 30-31)
1990: Jan. (7-9, 11, 14, 16, 18, 21-22, 24-25, 28),
Feb. (3-5, 11, 16-17, 19-20, 25-26, 28),
March (4-5, 8, 11-12, 18, 22, 25-26, 28), April (1, 8-10, 15-30),
May (1-4, 6, 8-9, 13, 17-21, 23, 27, 29-31),
June (3-5, 8, 10-12, 14, 16-20, 24-27),
July (1-3, 8-9, 12, 14-16, 22-25, 29-30),
August (5-6, 12-13, 19-23, 26-31), Sept. (2-18, 20-27),
Oct. (1, 6-9, 14-15, 20-31), Nov. (1-30),
Dec. (2, 4, 6, 9, 13, 15-17, 22-31)
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++++ start of p. *24 in SOO 8 +++++++++++++++++++++++++++++++
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TABLE 3.3. Species recorded per day of observation at Thornton Creek in 1973-1990. Days with five or less species/day are excluded; see Table 3.1 for number of observation days/month and Table 3.2 for dates with five or less species/day.
N=number of years, SD=Standard Deviation, #=No observation days and no bird records, *=in November 1990 only, some species were observed but the number of observation days was not recorded; AV=average of monthly means, SD=Standard Deviation, Range=minimum-maximum of species/day.
Species includes some taxa not identified to species (goose spp., stint spp., and jaeger spp.) but not others (Common/Red-breasted Merganser, Sharp-shinned/Cooper's Hawk, gull spp., Caprimulgidae spp., Empidonax spp., Audubon's [Yellow-rumped] Warbler, Myrtle [Yellow-rumped] Warbler, and Slate-colored [Dark-eyed] Junco).
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Species/Day of Observation....................
January....... February...... March.........
Yr Mean SD Range Mean SD Range Mean SD Range
73 # # # # # # # # #
74 12.2 2.7 9-20 12.1 3.4 7-19 16.3 4.1 9-25
75 10.4 2.7 6-16 12.8 3.1 6-21 13.1 3.8 6-22
76 11.5 3.4 6-17 13.9 3.5 7-21 17.1 4.6 9-28
77 14.9 3.6 8-22 16.6 4.8 9-24 19.0 4.5 9-28
78 16.6 4.6 11-23 16.5 3.7 11-24 20.3 5.1 14-32
79 16.0 2.7 10-21 12.8 3.0 9-19 16.0 3.4 10-22
80 13.9 3.0 9-19 14.1 3.9 9-25 17.4 4.6 9-25
81 11.6 3.7 8-18 13.2 2.3 8-17 14.2 3.9 9-22
82 15.2 2.7 12-20 13.6 2.2 11-20 14.5 4.1 8-22
83 11.2 2.0 8-14 11.4 2.8 8-19 13.2 2.8 8-21
84 13.0 3.3 7-19 14.3 3.3 8-20 20.9 5.3 13-32
85 12.9 3.1 7-19 13.8 3.7 8-23 14.9 3.9 10-24
86 18.3 4.8 11-30 16.5 2.7 13-22 22.6 5.3 15-30
87 15.8 4.8 14-25 20.6 4.8 15-26 20.2 4.2 15-30
88 17.7 4.4 10-27 14.4 3.4 10-21 18.7 4.5 10-28
89 16.4 2.4 11-19 19.5 2.1 17-24 18.9 1.9 15-21
90 18.6 4.5 12-29 16.6 2.4 13-21 22.8 2.8 17-28
Summary for Months with at Least One Observation Day
N 17 17 17
AV 14.5 14.9 17.7
SD 2.6 2.5 3.1
Range 6-30 6-26 6-32
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Species/Day of Observation....................
April......... May........... June..........
Yr Mean SD Range Mean SD Range Mean SD Range
73 16.8 5.6 8-29 23.5 5.2 13-30 25.9 5.7 13-38
74 21.3 5.9 11-32 29.3 5.7 15-39 28.2 5.4 13-37
75 20.1 4.7 14-33 28.1 5.9 19-40 27.3 3.8 17-35
76 22.6 4.8 14-31 28.0 5.0 20-40 32.1 5.0 22-45
77 27.8 5.6 14-40 35.3 4.3 27-42 33.9 4.3 28-43
78 26.0 5.6 17-37 36.6 4.9 20-45 32.1 4.1 25-38
79 24.6 6.1 15-39 34.9 3.7 29-41 31.2 3.3 24-38
80 25.8 6.3 15-40 31.8 3.9 24-38 31.2 2.7 27-38
81 24.1 8.3 13-35 34.5 4.6 26-43 32.2 2.8 28-37
82 23.7 7.1 14-38 37.1 5.1 26-47 33.6 2.8 29-38
83 25.1 6.3 14-36 35.0 5.2 21-43 35.7 3.8 30-44
84 26.9 3.6 19-33 31.2 5.6 17-39 30.0 5.3 22-40
85 23.6 5.6 14-35 38.4 3.8 29-45 35.1 3.8 29-45
86 26.6 7.1 14-36 39.8 6.5 25-50 38.4 2.5 34-42
87 29.2 7.0 17-42 40.4 4.7 33-50 36.2 3.6 27-41
88 29.7 7.2 14-44 34.9 4.8 24-42 30.0 6.0 10-38
89 26.6 6.1 18-36 32.2 3.8 23-37 30.5 4.1 25-36
90 26.8 3.2 23-32 32.6 5.0 19-40 32.3 4.2 25-41
Summary for Months with at Least One Observation Day
N 18 18 18
AV 24.9 33.5 32.0
SD 3.2 4.4 3.2
Range 8-44 13-50 10-45
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Species/Day of Observation....................
July.......... August........ September.....
Yr Mean SD Range Mean SD Range Mean SD Range
73 23.7 5.1 16-35 19.4 6.1 8-32 14.5 4.2 6-22
74 26.9 3.9 17-33 19.7 4.4 11-26 13.3 4.4 6-24
75 26.1 5.2 19-33 21.9 4.0 15-31 15.9 4.7 11-27
76 28.8 4.0 20-34 24.5 4.5 16-33 16.0 3.7 8-24
77 32.0 3.2 27-37 31.6 5.4 11-41 19.3 4.9 11-31
78 31.1 3.6 25-39 23.0 6.2 17-33 19.2 3.8 12-27
79 29.8 6.7 25-38 27.2 4.8 18-36 18.8 3.2 13-24
80 28.9 6.5 24-37 26.9 4.9 16-35 18.3 4.4 11-30
81 32.2 3.3 25-38 23.7 4.2 17-30 18.4 2.6 12-22
82 29.3 3.4 22-35 25.5 4.3 10-31 20.8 5.1 13-30
83 # # # 21.8 3.6 14-29 18.4 5.3 12-27
84 29.6 4.7 24-41 24.7 5.8 17-38 20.3 3.9 16-33
85 33.1 3.6 24-39 30.2 4.3 21-41 22.0 4.2 16-30
86 # # # 33.1 2.9 27-39 23.5 5.7 13-34
87 34.9 5.1 27-43 30.3 6.2 21-46 32.5 7.7 19-45
88 30.4 3.8 27-40 20.7 4.0 14-31 19.6 3.1 16-25
89 29.3 3.2 25-35 24.9 4.3 15-33 15.4 3.3 10-23
90 25.9 3.7 21-33 24.4 3.8 20-35 26.4 5.5 21-35
Summary for Months with at Least One Observation Day
N 16 18 18
AV 29.5 25.2 19.6
SD 2.9 4.0 4.5
Range 16-43 8-46 6-45
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Species/Day of Observation....................
October....... November...... December......
Yr Mean SD Range Mean SD Range Mean SD Range
73 15.3 4.4 10-24 9.2 2.8 6-14 9.4 1.8 6-15
74 17.0 4.3 9-25 9.5 2.8 6-15 9.4 2.6 6-15
75 16.2 3.8 11-26 11.9 4.1 6-18 12.0 3.4 6-19
76 16.4 4.1 9-23 12.6 3.9 6-22 12.6 3.7 6-20
77 21.8 5.2 14-31 17.2 3.9 10-25 17.5 3.3 14-25
78 16.2 3.8 11-26 14.7 3.2 11-24 14.7 2.7 10-19
79 17.1 4.0 11-26 14.1 3.8 10-23 14.4 3.0 10-20
80 15.5 5.2 7-27 11.4 3.0 6-17 11.1 3.6 8-18
81 17.0 3.8 9-23 15.3 3.5 10-22 13.7 3.9 6-21
82 15.9 4.8 7-25 9.1 2.6 6-16 8.3 2.1 6-13
83 17.9 4.2 13-26 10.6 2.4 6-15 14.1 3.0 9-18
84 14.0 5.0 9-29 10.8 2.5 7-15 11.5 3.8 7-20
85 17.2 4.4 11-28 14.8 3.6 9-21 18.6 4.0 12-26
86 21.9 4.3 12-30 # # # 16.6 4.5 9-24
87 25.9 5.4 13-34 17.0 4.1 7-26 15.9 4.4 12-24
88 26.1 4.6 15-34 15.8 4.3 10-23 13.8 3.7 11-18
89 22.5 4.3 14-28 14.9 3.9 10-24 18.0 3.2 13-24
90 25.4 3.4 19-31 * * * 19.2 3.1 14-25
Summary for Months with at Least One Observation Day
N 18 16* 18
AV 18.9 13.1 13.9
SD 4.0 2.8 3.3
Range 7-34 6-26 6-26
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TABLE 3.4. Number of species recorded each month and year at Thornton Creek in 1973-1990.
N=number of years, AV=1973-1990 monthly average, SD=Standard Deviation, MIN=monthly minimum, MAX=monthly maximum, *=number of observation days was not recorded, Total Species=total species each month during all years or total seen each year during 1973-1990.
Taxa included or not included as species are the same as in Table 3.3.
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Species/Month................................. Total
Yr Ja Fe Mr Ap My Jn Jl Ag Sp Oc Nv De Species
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1973 0 0 0 48 48 54 49 55 53 43 28 30 93
1974 37 36 44 58 63 54 46 52 48 45 31 26 95
1975 31 31 35 47 69 50 51 53 51 44 33 34 95
1976 35 37 38 61 65 58 53 55 52 45 33 35 97
1977 37 38 43 65 66 56 62 68 56 50 47 41 107
1978 36 37 47 62 78 59 62 59 53 43 34 34 104
1979 40 34 43 63 71 47 60 62 49 45 38 41 109
1980 37 36 43 56 71 53 53 46 48 50 37 32 97
1981 34 45 38 62 62 53 62 52 45 46 36 29 104
1982 34 28 35 62 75 61 52 51 45 47 31 28 107
1983 27 29 31 58 64 55 0 56 50 41 29 31 97
1984 33 34 48 56 64 58 51 53 52 43 29 29 100
1985 39 27 44 54 74 52 60 57 53 40 33 36 107
1986 44 33 38 66 71 52 0 61 56 45 0 30 99
1987 32 38 46 66 79 60 68 62 72 55 42 37 113
1988 38 35 44 61 63 58 52 48 49 52 33 35 99
1989 37 36 37 63 55 49 53 52 47 44 39 44 100
1990 36 34 43 50 58 51 45 50 57 51 36* 37 101
1973-1990 Summary for Months with at Least One Observation Day
N 17 17 17 18 18 18 16 18 18 18 17 18 18
AV 36 35 41 59 66 54 55 55 52 46 35 34 101
SD 4 4 5 6 8 4 7 6 6 4 5 5 6
MIN 27 27 31 47 48 47 45 46 45 40 28 26 93
MAX 44 45 48 66 79 61 68 68 72 55 47 44 113
60% of MAX 26 27 29 40 47 37 41 41 43 33 28 26 68
yrs of TOE 17 17 17 18 18 18 16 18 18 18 17 18 18
Total Species 67 66 72 111 112 91 93 109 105 89 75 71 192
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TABLE 3.5. Correlation of observation days/month, number of species/month, and average number of species/day at Thornton Creek in 1973-1990. These data were calculated from Tables 3.1, 3.3, and 3.4 for months with five or more observation days.
Since months varied markedly in the number of recorded species or the average number recorded per day, it was necessary to divide the year into intervals. Intervals below were chosen on the basis of similar numbers of average species/day in Table 3.3 and species/month in Table 3.4.
N=number of months used for comparison in each interval, r=correlation coefficient, @=less-than, P=two-tailed probability, NS=not significant (two-tailed P greater than 0.10). Statistical significance was tested with the student's "t" test given in Goldstein (1964:146) and Pollard (1977:261).
----------------------------------------------------------------------------
Obs. Days/Month Obs. Days/Month Species/Month
vs vs vs
Species/Month Av. Species/Day Av. Species/Day
Interval N r P r P r P
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November-February 68 0.15 NS -0.32 @0.01 0.60 @0.002
March 17 0.20 NS -0.43 @0.10 0.56 @0.02
April 18 0.07 NS -0.54 @0.05 0.62 @0.01
May 18 0.34 NS -0.10 NS 0.71 @0.002
June-August 52 0.34 @0.02 -0.30 @0.05 0.39 @0.01
September-October 36 0.02 NS -0.38 @0.05 0.67 @0.002
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CHAP. 4. DISCUSSION: GENERAL
In spite of the shortcomings just discussed in section 3-B, the value of these observations cannot be ignored. These records are the most extensive that have been published for the Oregon Coast Range. For example, based on monthly averages in Tables 3.1 and 3.3, Faxon has about 99,800 records, where each record is one species noted during one day.
In this Chapter, some of the general results are examined in more detail. Results pertinent to migration are discussed in Chap. 5, and results for individual species are given in Chap. 6.
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Faxon recorded a total of 191 species at Thornton Creek, 144 of which were classed as terrestrial (Table 4.1). The majority of waterbirds (54.6%) were found in only 1-3 years, but the majority (50.4%) of terrestrial birds were recorded in each of 16-18 years (Table 4.1). If there had been more suitable habitat for waterbirds, Faxon may have recorded more species, and each species might have been recorded more regularly.
The large number of species at Thornton Creek is more a result of Faxon's diligence than of an abundance of species. If Faxon had not spent an average of 19-24 observation days per month during 209 months (=17.4 years) (Table 3.1), while he worked out of doors most of the day, he would have recorded fewer species (also see section 4-G).
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The average number of species seen per day during 1973-1990 ranged from 13.1 to 33.5 with the greatest daily average recorded in May when a peak of 50 species/day was noted twice (Table 3.3). However, daily means greater than 30 were also often found in June and sometimes in July-September, so these months had averages of over 25 birds/day (Table 3.3).
November-January daily averages were less than half those in May-July (Table 3.3).
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For the 1973-1990 period, the average number of species per month ranged from 34 to 66 with a maximum of 79 species (Table 3.4). Generally the greatest number of species was found in May, although in many years there was a secondary, smaller peak in July, August, or September (Table 3.4). Generally, the number of species was less in June than in April (Table 3.4).
The least number of species per month was observed from November through February, when the average was about 52-55% that of May (Table 3.4).
Combining all years, the total number of species/month ranged from 66 to 112 with April-May and August-September having over 100 species/month (Table 3.4).
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In general, Faxon's observation effort varied (section 3-B-3), and this could account for some of the variation in the number of species/day (section 4-C) and species/month (section 4-D). But the variation in his observation effort may also account for some of the variation in the frequency of presence of individual species during a year and among years that is given in the individual species' accounts in Chap. 6. In particular, the absence or low frequencies of some species in some months may be because they were overlooked, not because they were absent.
It would, however, be a mistake to assume that species are constantly present; some are just passing through and others may have large home ranges that may make them difficult to be seen daily. Further, the variation in many summer or winter resident species' presence after they arrive (section 5-D) could very well be because they are not present then every day; unfortunately, no one besides Faxon has data to test this. This variation among years in arrivals or departures is examined in sections 5-C and 5-D.
In conclusion, some of the variation in the frequency of a species' presence may be a result of observation effort variation, but some may also be because a species may vary in its presence.
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The interrelationship between species is a very complex issue, and one with which I have made no real attempt to spend a great deal of time studying. Nevertheless, I have made a number of observations over the years about changes in populations that seem on the surface to be more related to pressures from the birds themselves than from anything else. These are admittedly subjective opinions of what I have observed, and there are no hard figures to back them up, but my years of observations should give them some credibility.
First of all, the coming of two alien species to the Valley has contributed more than anything else to the reorganization of bird populations. In 1957, Brown-headed Cowbirds first arrived here, and European Starlings followed in 1969. Each has brought changes to the Valley's bird life, but in different ways.
The most notable change brought about by the cowbirds (section 6-B-184) was probably in breaking up a colony of about 20 pairs of Brewer's Blackbirds (section 6-B-183) that had been permanent residents in the Thornton Creek Valley.
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Brewer's generally built their nests in somewhat conspicuous places, such as an exposed fork of a tree, and certainly would have been a vulnerable species for cowbird parasitism. Whether this, in fact, happened is open to question, but within just a couple of years after 1957 the colony of blackbirds broke up completely, and none have bred here since. Now, the species is only an occasional straggler here. If, in fact, cowbirds were responsible for this, why Brewer's remain such a common species in so many other places but were unable to adapt in this location remains a mystery.
Brewer's Blackbirds, of course, are not the only species which are parasitized by cowbirds. I have observed Wilson's and Black-throated Gray warblers, Song and White-crowned sparrows, and Hammond's Flycatchers feeding young cowbirds, but the cowbird's effect on these species is unknown. It probably has not caused any major disruption to them, as the number of cowbirds in the Valley has never numbered more than about 15 adults.
The problem caused by starlings (section 6-B-142) appears to be much worse. They have been hard on cavity-nesting species, swallows and some woodpeckers in particular. Tree and Violet-green swallows formerly nested in old woodpecker holes and natural cavities, but the starlings have taken over all such nesting sites, at least in the general vicinity of the house and barns, and even further back up the canyon. I have sometimes destroyed starling nests and shot adult starlings, but it seems to have had little effect on their population. They remain as aggressive as ever, and quickly become wary.
There is little doubt that the influx of starlings reduced the populations of some woodpeckers, particularly Downies (section 6-B-91). Before the coming of starlings, Hairy and Downy woodpeckers were equally common birds. Now the Hairy is an uncommon species (section 6-B-92), and the Downy is quite rare. Perhaps the Hairy has not suffered as badly because its larger size allows it to sometimes compete for nesting space with starlings. Northern Flickers are frequently seen fighting starlings over nesting space, and flickers remain quite common (section 6-B-93).
An interesting thing took place in respect to the population ratio of Tree and Violet-green swallows (sections 6-B-107 and 6-B-108, respectively). Prior to the arrival of starlings, Tree Swallows were more abundant than Violet-greens. This became even more pronounced with the coming of the starlings. The Violet-greens dwindled down to one nesting pair.
About that time I put up about a dozen nest boxes suitable for swallows. The result was that the population of Violet-greens exploded, and at the same time the population of Tree Swallows diminished. Now there are around eight nesting pairs of Violet-greens, and only about two or maybe three pairs of Tree Swallows. There seems to be no reasonable explanation for this reversal of swallow populations.
There is one other case of competition between species that has no relationship to invading or non-native species, and it is perhaps the most interesting one of all. It is between two vireos, the Solitary and the Warbling (sections 6-B-143 and 6-B-145, respectively). The Warbling is much more common, nesting throughout the Thornton Creek Valley in suitable habitat, while Solitary Vireos have never numbered more than three pairs. However, the competition for space between the two species is apparently very keen, as both prefer similar habitats.
The Solitary Vireo annually arrives ahead of the Warbling by an average of eight days. Immediately upon arrival, a Solitary Vireo stakes out a territory. Since vireos, and Solitary Vireos in particular, are persistent singers, their territorial boundaries are often easy to define. I have been fortunate enough to be able to work in a couple of different areas where this territorial behavior was taking place. I observed several Solitary Vireos each stake out a territory that was a nearly square area. Each vireo made a complete round of the outer boundaries of its square several times a day. This continued steadily right up to the time when the Warbling Vireos arrived.
The Warbling Vireos have apparently adapted to being able to survive within a smaller territory than Solitary Vireos, so when Warbling Vireos arrive, several different Warbling Vireos quite often begin to put pressure on the edge of the territory that a Solitary has already staked out. This no doubt creates a certain amount of stress on a Solitary that was the first inhabitant of the area.
Although I have not observed any specific confrontations between the two species, the pressure Warbling Vireos exert on the edge of a Solitary's territory invariably seemed to cause the territory to decrease in size, even though the territorial Solitary still continued to sing and move around. In some cases, when the boundaries became too small, a territorial Solitary simply gave up and left.
Prior to 1966, coyotes were unknown here. Now they are common, and some years have been abundant. I have no doubt that they have contributed to lower populations of ground-nesting and ground-dwelling birds.
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I should add a few paragraphs about what have come to be called vagrants. Seeing the rare bird remains an exciting part of birding, so some treatment of that should be done here.
The Thornton Creek Valley has had its share of rarities over the years, but that must be put in perspective. First of all, in 37 years almost anyplace would have its share of rarities. Secondly, one must remember that my work enables me to be outside most of the time during each day. Thus, I have spent thousands of hours in the field and have had ample opportunity to spot any rare individual that might have come by.
Actually, Thornton Creek is not to be considered a hot spot for rare birds, although it can be on occasion if conditions happen to be just right. Since the Valley basically lies north and south, it serves as a natural route for birds during migration. Most of the upper portion of the watershed is a solid forest, with little to force the migrants into a small area. However, once the Creek enters the area nearest the House (see Fig. 2.1) that changes. Then there are several pastures adjoining the Creek, and the trees that are present are right on the Creek for a distance of nearly half a mile. Birds using the Valley as a route for migrating are thus forced into a narrow strip of trees there, and this makes for good birding during migration, particularly in fall.
++++ start of p. *28 in SOO 8 +++++++++++++++++++++++++++++++
Other vagrants have shown up at various times of the year, most notably in late spring, but there is not really enough of a pattern to most of these sightings to make any concise statement concerning them.
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TABLE 4.1. Number and regularity of water and terrestrial birds at Thornton Creek.
Waterbirds=grebes, cormorants, herons, egrets, waterfowl, Osprey, rail, shorebirds, jaegers, gulls, and Belted Kingfisher (including goose spp., stint spp., and jaeger spp.); but not Common/Red-breasted Merganser or gull spp.
Terrestrial birds=all taxa not previously mentioned except Sharp-shinned/Cooper's Hawk, Caprimulgidae spp., Empidonax spp., Audubon's and Myrtle (Yellow-rumped) warblers, and Slate-colored (Dark-eyed) Junco.
No. Years Found=number of calendar years in which a species was recorded at least once out of a total of 18 years (1973-1990).
----------------------------------------------------------------------------
No. of Species............
Water Terrestrial Total
--------------------------------------------------
pre-1973 only 3 9 12
1973-1990 44 135 179
Total 47 144 191
----------------------------------------------------------------------------
1973-1990.....................
No. Years % of Species......
Found Water Terrestrial
-----------------------------------
1 29.6 20.0
2 15.9 4.4
3 9.1 5.2
4 4.5 2.2
5 4.5 3.0
6 0 1.5
7 6.8 1.5
8 0 0
9 0 0.7
10 0 0.7
11 4.5 1.5
12 6.8 1.5
13 0 1.5
14 0 3.7
15 2.3 2.2
16 2.3 2.2
17 2.3 5.2
18 11.4 43.0
TOTAL 100.0 100.0
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++++ start of p. *29 in SOO 8 +++++++++++++++++++++++++++++++
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CHAP. 5. DISCUSSION: MIGRATION
Although it may seem that determining which species are migratory would be a simple task, it is not so in all cases. Species that are only regularly present during a particular portion of the year are probably migrants. But species in which some birds are present throughout the year may also have subpopulations that are migratory. For example, Reed Ferris' banding data for the Tillamook County Coast Range indicate that some Song Sparrows appeared to be nonmigratory, but that others seemed to be only winter residents (Bayer and Ferris 1987:29, 37-38). Unfortunately, Faxon's data indicate only when a species is present or absent, not when particular individuals are present or absent. Thus, species that appear to be nonmigratory at Thornton Creek may still have migratory subpopulations.
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Unfortunately, migration is not as easy to measure as one would suppose because not all birds arrive or leave together.
When considering a species' arrival and departure dates, the first problem is to determine what to measure: the date when a species is first or last detected or the date when the species is first or last COMMONLY present?
Customarily, birders and researchers (e.g., Saunders 1959) often think of First (arrival) or Last (departure) dates as when a species is first or last detected, and that is the way these dates have been calculated in this Volume. Since it is clear that some species may not be present every day after they first arrive or before they last depart (sections 5-C and 5-D), accurate determination of yearly First and Last dates is highly dependent on observation effort as well as sporadic presence of a species at the onset of immigration or the outset of emigration. Since the adequacy of observation effort in determining First or Last dates is unknown, it is not reasonable to assume that First and Last dates (and subsequent averages) are extremely accurate.
If dates when species are first or last COMMONLY present are desired, then dates have to be calculated differently. For example, Temple and Cary (1987a) determined first dates by using the date when a species was first recorded at 50% of its average frequency. This was considered infeasible for Faxon's observations.
There are several sources of error in determining arrival or departure dates each year. First, and most obvious, is that few or no observations were made some days (Table 3.2), and species may have been overlooked on observation days when the number of species recorded were less than the average recorded that month (Table 3.3). Thus, a species may actually have been present earlier than the observed First date and later than the observed Last date but may have been missed or overlooked.
The second source of error is one of interpreting unusually early or late birds. The early arrival or late lingering of one, perhaps immature, abnormal, or sick bird could affect the observed arrival or departure date for the whole species in that year. Exclusion of atypical dates has been done to a certain extent with Faxon's data, but such decisions are highly subjective and generally were not done. Thus, it would be ideal if arrival/departure dates are only determined for a significant number of birds, not one or a few abnormal birds. Unfortunately, this is difficult to determine in the field.
A third problem is of mistaken human judgment in oversimplifying the categorization of bird species as just residents or migrants. For example, Varied Thrushes (section 6-B-136) can be classed as winter residents, but they are more frequent in October than in the rest of winter, so some may only be fall migrants while others are winter residents. Another example is the Golden-crowned Sparrow (section 6-B-176), which can also be classed as a winter resident; however, they have much higher frequencies in April than throughout the rest of the winter, probably as a result of an influx of spring migrants. Similarly, Reed Ferris' banding results in the Tillamook County Coast Range indicate that some Golden-crowned Sparrows were winter residents, but that most were spring migrants (Bayer and Ferris 1987:29). A third example is of some summer resident species, in which part of the population is just spring migrants, while others are summer residents. Examples of two summer resident species at Thornton Creek that appear to be just spring migrants at some other Coast Range sites in Lincoln County are White-crowned Sparrows and Black-throated Gray Warblers. In all these examples, there should be an arrival and departure date for each portion of the population; having a single arrival and departure date is an oversimplification and is in error. Nevertheless, determining multiple arrival and departure dates for these species is difficult to do in the field.
If there were three or more years with First or Last dates, an Average First or Average Last date is calculated. Although such averages are commonplace (e.g., Saunders 1959), Bayer has misgivings about them because if yearly dates are inaccurate, then the average will be in error. If the error in yearly dates is random, then the error could be expected to cancel out by using an average, but the error is not random. The error for First dates will be consistently in using dates later than a species' actual arrival date, and the error for Last dates will be consistently in using dates before a species' actual departure date.
++++ start of p. *30 in SOO 8 +++++++++++++++++++++++++++++++
To more accurately determine an average, it would be helpful to determine which First or Last dates may be so inaccurate that they could be discarded; perhaps, use of statistical methods to eliminate outlier data would be useful. Although some apparent abnormal First or Last dates have been excluded, the problem is determining if outlier data represent inadequate observation effort or a species' abnormal migration, perhaps because of abnormal weather (e.g., Welty 1962:462-466, Pettingill 1967:179) or of abnormally behaving birds. Further, it is apparent that the wide range in First or Last dates at Thornton Creek is not unique, since Saunders (1959) also often found large variability in First and Last dates in Connecticut.
Bayer has puzzled over alternatives to Average First or Last dates but has not found anything demonstrably better. For example, an average could be made of the two, three, or five earliest or latest First or Last dates. Such an average would be more useful than the average of all First and Last dates in preparing observers for the arrival or departure of a species, but such an average may not be typical for most years and would not be as useful in predicting a species' presence in a particular year as an overall average. Accordingly, overall averages are still used, but the reader is cautioned that they may not be accurate. Further, the reader is cautioned that First or Last dates may be site- and observer-specific, so that extrapolating the First or Last dates from one site or one observer to another may not be accurate.
While Average First and Last dates are biased estimators of when a species First or Last appears, these Averages may be better estimators of when the species is first or last regularly present. This could result because Faxon may have detected birds when they were common, not when only a few individuals were sporadically present.
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Do birds arrive and then remain every day?
Most of them apparently do not do so at Thornton Creek. A perusal of many of the species accounts indicates that many species were not found every day in the month after they first arrived; for example, they had monthly frequencies of less than 9-10 tenths.
Further, only three (Willow Flycatcher, Swainson's Thrush, and Black-headed Grosbeak) of 23 common summer residents and none of the four common winter residents were present in 90% or more of the observation days in the 10 day period after they were first recorded (Table 5.1).
Based on monthly frequencies of most birds prior to their last recorded date, most birds did not appear to depart abruptly from Thornton Creek. Further, none of the 23 common summer residents or four common winter residents were present in 90% of the days in the 10 day period prior to their departure (Table 5.1).
Most (17) of the 23 summer residents were more frequent after their arrival than before their departure (Table 5.1). But the Band-tailed Pigeon and Western Wood-Pewee were much more frequent before their departure (Table 5.1).
Of the four common winter residents, only the Varied Thrush was more frequent after its arrival than prior to its departure (Table 5.1). In contrast, the Golden-crowned Sparrow was much more frequent before its departure than after its arrival (Table 5.1).
Even though Faxon's data seem to indicate that a species does not depart abruptly, this may be misleading because the vast majority of a species may leave en masse (e.g., section 5-G-3), although stragglers may remain and prolong the observed departure date for the species as a whole.
One probable reason for the infrequency is because birds can be highly mobile and asynchronous in their arrival and departure. Thus, there are days when they are present and other days when they are not. For example, some birds may be just passing through during migration and do not remain at one site, even for species in which some birds remain as winter or summer residents. Other birds may remain in the general area but may be searching for favorable habitat to remain to nest (i.e., the summer residents) or to overwinter (i.e., the winter residents) and thus may not remain in an area where they would be observed by Faxon.
A second reason is that some species may be more frequent than Faxon's data suggest. Faxon may have missed birds because they were inconspicuous or less numerous when they first arrived or when they departed. Faxon may also have missed birds because they were present when he wasn't looking during a day.
To conclude, it is not possible to determine if a species' infrequency at the time of its arrival or departure is characteristic of a particular species or is because a species was overlooked. Unfortunately, no one else has made daily observations in Lincoln County to compare with Faxon's results. In any case, this infrequency is characteristic of Faxon's observations.
The observed infrequency is significant for two reasons. First, it indicates that summer and winter residents may often be absent after their "arrival" or before their "departure."
Second, it suggests that arrival or departure dates can be very dependent on daily observation effort, at least for Faxon's observations. For instance, if there are inadequate daily observations, then the actual date when a species may arrive or depart may be missed, and it may be several days or a week (e.g., for species present 30% or less of the days after the arrival date in Table 5.1) before the species may appear again. Thus, apparent differences in arrival or departure among years may be partially a result of uneven observation effort among years.
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Given the infrequency of presence of many species within 10 days of their arrival (Table 5.1), it is not surprising that most common summer and all common winter residents were infrequently seen on the date of their average arrival (Table 5.2). In fact, only five of 23 common summer residents were seen on 50-75% of the dates of their average arrival, and none were seen on more than 75% of the dates of their average arrival (Table 5.2). Further, not one of the four winter residents was found on an average of greater than 25% of their average arrival dates (Table 5.2). Finally, the average frequency of presence for the average arrival day plus or minus five days was above 50% for only one species, the Barn Swallow (Table 5.2).
These low frequencies indicate that the presence of these common summer and winter residents on the date of their average arrival is unpredictable. Even 3-5 days after the average arrival date, the average frequency of presence for the 23 common summer resident species was only 50-61% and for the four common winter residents was only 24-34% (Table 5.2), which indicates that their presence then is still unpredictable.
For a common summer resident, the frequency of occurrence on the average arrival date (Y)(% on day=0 in Table 5.2) is somewhat correlated with the frequency with which a species is noted 10 days after it first arrives (X; "First + 10 Days Mean Presence Frequency" in Table 5.2) and inversely correlated with the extent of the range between the minimum and maximum yearly arrival dates (R; "First Date Range" in Table 5.2). For example, for the 23 summer residents, the correlation between Y and X was r=0.44 (student's t=2.23, two-tailed P less than 0.05) and between Y and R was r=-0.41 (student's t=2.04, two-tailed P less than 0.10).
For the 23 common summer residents, the multiple linear regression of the relationship between Y on both X and R can be expressed as Y=25.44 + 0.29X - 0.57R. This regression was statistically significant (F=3.72, one-tailed P less than 0.05). However, the coefficient of determination (Zar 1974:260) for this regression was only 0.272, so only 27.2% of the variation in Y was accounted for by X and R. Thus, usage of only X and R to predict Y can be inaccurate.
One source of error in these calculations is that Faxon did not make observations every day (see Table 3.2), so birds may have arrived earlier than indicated. Hence, their average arrival date would be prior to the one calculated. Given that summer and winter residents were usually more infrequent before the calculated arrival date, this source of error would result in birds being even more infrequent on the date of their average arrival than indicated in Table 5.2.
A second source of error is that birds may have been missed on some observation days. Thus, some of the variation in the regression and correlation analyses may be due to observation omission error rather than error related to the presence of summer residents when they arrive.
Because there were only four common winter residents, multiple linear regressions and correlations were not calculated for their arrivals.
These calculations were also not done for departures because Bayer expected these birds to be infrequent on the date of their average departure, similarly to their infrequency on the date of their average arrival. The major difference would be that they would be expected to be more frequent in the days prior to the date of their average departure.
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Saunders (1959) compared arrival dates of spring migrants in Connecticut with average arrival dates and sometimes with weather conditions. Such analyses could also be done with Faxon's arrival/departure data and his monthly rainfalls (Table 2.1) or daily rainfall and temperature records kept at Toledo or Newport. Bayer has not done this because in scanning some of the records for swallow arrivals, he did not see an obvious correlation with rainfall at Thornton Creek.
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There is no indication of raptor migration during the spring at Thornton Creek. However, if Faxon had spent more time watching ridge tops during spring he may have noted flights of raptors because several species have been observed migrating along ridge tops near the coast in California (Fish 1989). However, the average migration rate in California of 9.3 raptors/hr (which is about one raptor every 6.5 min)(Fish 1989) is so low that a spring raptor migration could have been easily missed at Thornton Creek.
Faxon did not note any waves of migrants in spring.
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Because of their increased frequencies in fall at Thornton Creek, Turkey Vultures (section 6-B-27), Northern Harriers (section 6-B-30), and Sharp-shinned Hawks (section 6-B-31) appear to migrate through Thornton Creek. These raptors as well as Cooper's and Red-tailed hawks (sections 6-B-33 and 6-B-36, respectively) are also migrants along ridge tops near the coast in California (Fish 1988), where the average migration rate was 17.4 raptors/hr (which is about one raptor each 3.5 min).
Fall migration of raptors might have been more detectable at Thornton Creek if Faxon had spent more time watching ridge tops. But with an average rate of only one raptor every 3.5 min as in California, Faxon would have had to been very patient to detect a migration.
Sometime from early August until early September there is commonly a major movement of migrants at Thornton Creek. This movement is most observable around 9 AM.
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On days when it is raining or overcast, actual waves of migrants sometimes occur. Faxon has then noted up to six species of migrants in a single tree at the same time. Most often these waves of migrants include Black-throated Gray and Wilson's warblers, Warbling Vireos, Black-headed and Evening grosbeaks, Western Tanagers, and Empidonax flycatchers with a sprinkling of other species including occasional Townsend's Warblers and vagrant warblers.
The Empidonax flycatchers remain the most puzzling part of the fall movement. Each fall there are several of them which pass through the Valley that certainly do not appear to be any of the native species. A good mist-netting program here in the fall might turn up some real surprises.
The following incidental notes for fall migration in 1985-1988 are incomplete and subjective, but do indicate that waves of migrants can sometimes occur. Waves of migration could have also occurred on days other than those indicated.
In 1985, fall migration was slow until August 13, then a whole flood of migrants moved through. August dates of major movements were August 13th (grosbeaks, Western Tanagers, Warbling Vireos, and Empidonax flycatchers), August 15th (mainly grosbeaks with a sprinkling of Black-throated Gray Warblers), August 19th (a very heavy movement of Warbling Vireos, dozens of Black-throated Gray and Wilson's warblers, and a few Orange-crowned and Hermit warblers), and August 21st (another movement of primarily Black-throated Gray Warblers). The movement between these dates was more subdued, with fewer birds.
In 1986, by early August, a heavy migration of Black-throated Gray and Wilson's warblers, Warbling Vireos, Black-headed Grosbeaks, Western Tanagers, and Pacific-slope and Hammond's flycatchers was taking place. Later in August and in early September, large flocks of Evening Grosbeaks and Cedar Waxwings showed up.
In 1987, there was a heavy movement of passerines between August 26 and September 10. This movement was noteworthy for heavy concentrations of Red-breasted Nuthatches, Evening Grosbeaks (hundreds), Cedar Waxwings (thousands--single flocks of 300 birds were common), and Warbling Vireos. There were lesser numbers of Hammond's and Pacific-slope flycatchers, Black-throated Gray and Wilson's warblers, Western Tanagers, and a few Solitary Vireos. Townsend's Warblers moved through on September 7-8, but good numbers of them were still migrating through on October 15.
In 1988, a series of waves of migrants occurred during or shortly after periods of stormy wet weather. A small movement of Red-breasted Nuthatches began on September 15. On September 19, the day following a heavy rainstorm, there was a day-long movement of Black-throated Gray and Townsend's warblers and large numbers of Hammond's Flycatchers. During the first two weeks of October, there was an impressive movement of Ruby-crowned Kinglets. Another wave of Black-throated and Townsend's warblers occurred on October 3-10; a Yellow Warbler joined the group on October 5. Straggling Black-throated Gray Warblers were noted until October 13. On October 13, hundreds of Cedar Waxwings and American Robins moved through.
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TABLE 5.1. Mean and range in yearly frequency of occurrence of 23 common summer residents and four common winter residents at Thornton Creek within 10 days of arrival or before departure. Summer residents arrive in spring and depart in late summer/fall; winter residents arrive in late summer/fall and depart in spring.
These data are based on a sample of five years (usually 1976-1980), when the number of observation days each month and the number of species seen daily were usually higher than average (Fig. 3.1). If there were less than five days of observations in the 10 day period, a different year was usually used. These data are derived from summary data given for each species in Chap. 6.
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5 Year Frequency (%).......
First Date + Last Date -
10 Days..... 10 Days.....
Mean Range Mean Range
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SUMMER RESIDENT:
Turkey Vulture 35 20-50 42 14-63
Band-tailed Pigeon 22 0-33 68 33-100
Rufous Hummingbird 32 0-88 34 0-78
Olive-sided Flycatcher 76 44-100 64 10-100
Western Wood-Pewee 42 0-89 70 0-100
Willow Flycatcher 95 88-100 81 60-100
Hammond's Flycatcher 54 43-70 12* 0-33*
Pacific-slope Flycatcher 68 40-89 34 0-100
Tree Swallow 58 0-100 58 29-100
Violet-green Swallow 57 22-100 34 25-44
No. Rough-winged Swallow 43 0-100 23 0-60
Barn Swallow 74 44-89 73 17-100
Swainson's Thrush 93 67-100 44 11-57
Cedar Waxwing 59 13-100 14 0-38
Warbling Vireo 65 30-89 41* 0-78*
Orange-crowned Warbler 77 29-100 17 0-50
Black-thr. Gray Warbler 72 56-89 24 0-75
Wilson's Warbler 81 56-100 25 0-63
Western Tanager 26 0-67 32 0-63
Black-headed Grosbeak 98 90-100 67 0-100
White-crowned Sparrow 79 30-100 58 33-75
Brown-headed Cowbird 79 50-100 47 29-90
American Goldfinch 88 60-100 26 0-57
Mean 64 43
* Mean and range for only four years.
WINTER RESIDENT:
Ruby-crowned Kinglet 27 0-67 37 10-100
Varied Thrush 55 38-78 25 10-43
Fox Sparrow 40 13-88 40 14-78
Golden-crowned Sparrow 18 0-44 69 30-100
Mean 35 43
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TABLE 5.2. Frequency of presence five days before or after the average arrival date of 23 common summer residents and four common winter residents at Thornton Creek. Summer residents arrive in spring and depart in late summer/fall; winter residents arrive in late summer/fall and depart in
"First + 10 Day Mean" frequency is from Table 5.1 and is the frequency of presence within the first 10 days after a species' arrival. "Mean First Date" is the average First Date for all or part of the 1973-1989 period, and "First Date Range" is the difference between the largest and smallest First Date during the same period; these data are derived from yearly data for each species in Chap. 6.
"Frequency of Presence Before or After the Average First Date" is calculated by determining if a species was present/absent on a certain calendar date relative to the average first date for Faxon's 1973-1989 observations. If no observations were made on a day, then that day (and year) is excluded. For example, there were 17 years of April observations in which the presence of Band-tailed Pigeons in the five days before and after the average arrival date were determined; however, there were no observations on April 18 (-2 days [before the average]) in 1976 and 1982, so the frequency of presence is calculated from the presence/absence in the remaining 15 years for -2 days. Since the number of years with observations for each date vary, the range in the number of years with observations is given as the "Years/Day Range."
Only years in which a First Date were given for each respective species are included; see footnotes to see which years were included in these calculations.
Day 0=Average First Date.
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First + 1973-1989
10 Day Observations
Mean First
Presence Mean Date
Frequency First Range
(%) Date (Days)
----------------------------------------------------
SUMMER RESIDENT:
Turkey Vulture 35 3/18 18
Band-tailed Pigeon 22 4/21 29
Rufous Hummingbird 32 3/6 23
Olive-sided Flycatcher 76 5/10 18
Western Wood-Pewee 42 5/7 21
Willow Flycatcher 95 5/24 14
Hammond's Flycatcher 54 5/1 28
Pacific-slope Flycatcher 68 4/25 23
Tree Swallow 58 3/2 57
Violet-green Swallow 57 3/13 32
No. Rough-winged Swallow 43 4/11 37
Barn Swallow 74 4/11 13
Swainson's Thrush 93 5/10 12
Cedar Waxwing 59 5/23 21
Warbling Vireo 65 4/28 24
Orange-crowned Warbler 77 4/7 22
Black-thr. Gray Warbler 72 4/18 19
Wilson's Warbler 81 4/17 18
Western Tanager 26 5/9 12
Black-headed Grosbeak 98 5/7 13
White-crowned Sparrow 79 3/28 18
Brown-headed Cowbird 79 4/15 28
American Goldfinch 88 4/23 20
Mean 64 - 23
Minimum 22 - 12
Maximum 98 - 57
WINTER RESIDENT:
Ruby-crowned Kinglet 27 10/1 54
Varied Thrush 55 9/23 26
Fox Sparrow 40 9/20 38
Golden-crowned Sparrow 18 10/17 97
Mean 35 - 54
Minimum 18 - 26
Maximum 55 - 97
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1973-1989 Observations..................................
Days Before or After Average First Date.................
Years/
Frequency of Presence (%)....................... Day
-5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 Mean Range
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SUMMER RESIDENT:
Turkey Vulture 8 7 31 15 0 8 20 20 46 27 46 21 10-14A
Band-tailed Pigeon 7 7 20 8 19 25 14 21 20 31 43 20 13-16I
Rufous Hummingbird 17 8 25 20 31 17 50 36 45 36 27 28 10-14A
Olive-s. Flycatcher 15 23 23 21 36 29 38 46 45 69 50 36 11-14B
Western Wood-Pewee 12 20 21 25 29 23 20 25 47 36 47 28 13-17I
Willow Flycatcher 25 30 18 22 38 54 38 85 73 75 83 49 8-13C
Hammond's Flycatcher 22 10 13 38 33 38 31 36 20 36 70 32 8-13D
Pac.-sl. Flycatcher 0 7 17 33 50 9 55 67 64 82 82 42 11-15E
Tree Swallow 9 0 10 20 25 8 17 10 15 25 9 13 9-13A
Violet-green Swallow 29 27 27 18 27 15 31 46 62 64 42 35 11-14A
No. Rough-w. Swallow 13 21 27 33 15 15 25 29 38 31 36 26 12-16I
Barn Swallow 19 22 40 33 29 54 58 79 75 81 80 52 12-16I
Swainson's Thrush 7 0 0 27 40 20 50 47 55 85 93 39 11-15I
Cedar Waxwing 8 15 10 33 30 46 64 63 50 64 58 40 8-14F
Warbling Vireo 7 21 8 8 36 31 39 54 47 41 53 31 13-17I
Orange-cr. Warbler 7 20 38 33 38 57 47 38 42 58 58 40 12-16I
Black-t. Gray Warbler 0 17 17 27 40 75 56 58 58 70 89 46 9-12D
Wilson's Warbler 0 21 13 6 20 57 60 54 80 75 79 42 13-16I
Western Tanager 8 7 8 25 14 23 23 38 29 55 64 27 11-14G
Black-hd. Grosbeak 12 7 15 20 38 46 47 67 73 93 93 46 13-17I
White-cr. Sparrow 18 30 30 17 22 11 30 36 58 67 82 36 9-12H
Brown-headed Cowbird 8 15 8 7 13 25 21 29 47 46 60 25 12-16I
American Goldfinch 20 21 27 13 29 31 29 43 54 50 69 35 13-16I
Mean 12 15 19 22 28 31 38 45 50 56 61 34
Minimum 0 0 0 6 0 8 14 10 15 25 9 13
Maximum 29 30 40 38 50 75 64 85 80 93 93 52
WINTER RESIDENT:
Ruby-cr. Kinglet 11 10 0 0 18 15 23 27 30 30 29 18 9-15E
Varied Thrush 0 14 0 11 23 15 38 33 36 33 36 22 9-14J
Fox Sparrow 27 8 0 0 23 25 13 31 15 46 17 19 8-13J
Golden-cr. Sparrow 29 33 25 21 14 23 30 22 13 25 25 24 8-16I
Mean 17 16 6 8 20 20 26 28 24 34 27 21
Minimum 0 8 0 0 14 15 13 22 13 25 17 18
Maximum 29 33 25 21 23 25 38 33 36 46 36 24
A 1974-1985 and 1987-1989. F 1974-1989.
B 1973-1987. G 1974-1987 and 1989.
C 1973, 1975-1983, and 1985-1989. H 1974-1979, 1981-1985, and 1987-1989.
D 1977-1989. I 1973-1989.
E 1975-1989. J 1973-1981 and 1983-1989.
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