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Chestnut Ridge Hawk Watch - 2000
Species Accounts
By Tait Johansson
Click for
Seasonal Summary
In each individual species account, I compare this year's
numbers with the average for that species per 510 hours of observation time,
first for the last 8 years, then for the first 17 years of the watch's
operation. I then compare the first 9 years' data with the next 9 years'. I use
the 510 hr. average because there have been significant differences from year to
year in amount of coverage in a season. Past seasons have ranged from a low of
441.5 hours in 1984 to a high of 709.0 hours in 1987, potentially distorting any
comparison between seasons. Further, using a birds per hour figure to avoid this
problem (as does Tessaglia-Hymes, 1996) results in data which are somewhat
difficult to fathom. For example, the number of Cooper's Hawks per observation
hour for the last 9 years (including 2000) is about 0.566, whereas the number
for the first 9 years of the watch is about 0.280. While it is clear this
represents about a doubling of the numbers of this species, I find it difficult
to grasp clearly what 0.286 more Cooper's Hawks going by each hour really
amounts to. If we look at Cooper's Hawks per 510 observation hours (about the
length of an average season), however, we get 142.99 for the first 9, and 288.51
for the following 9, 145.52 more birds per (approximate) season, resulting in a
clearer comparison.
Black Vulture (Coragyps atratus)
18 Black Vultures were observed this season on dates
ranging from 9/13 to 11/3, an all time high for a season. This compares with an
average of 2.49/510 observation hours in the previous 8 years, and 1.08/510
observation hours for the whole 17 years (none at all having been observed in
the first 11 years of the watch). The highest day total for this species came on
10/22, with 7.
This species has been expanding its range northward
dramatically in recent years, and increasing its numbers in the Westchester
county area, and this year's numbers certainly reflect this. There is some
question about whether Black Vultures migrate at all. The Black Vulture is
essentially non-migratory (though spring counts in Texas give evidence to the
contrary).[HIFp.133]
The criteria we used for counting Black Vultures as migrants
were the same as for Turkey Vulture and all other species: a bird was counted if
and only if it was headed in a NW, W, S or SW direction in a fairly purposeful
manner, and did not, as far as we could tell, come back.
1st 9 years: 0.0 Last 9: 4.20
Turkey Vulture (Cathartes aura)
2,028 Turkey Vultures were observed, on dates
ranging from 9/29 to 11/20. This is another all time high for a Chestnut Ridge
season. This compares with an average of 773.14/510 hrs. in the last 8, and with
639.68/510 hrs. in the last 17. The highest number in a day was 191, on 10/22.
Turkey Vultures have only fairly recently (1950's and 60's) moved into the area,
and the increasing totals at Chestnut Ridge may reflect continued range
expansion to the North, and perhaps still-increasing numbers in this region.
1st 9: 537.51 2nd: 911.85
Osprey (Pandion haliaetus)
327 Ospreys were observed, on dates from 8/30 to
11/9. This compares with an average of 339.78 for the last 8 and 364.92 for the
last 17. Our biggest day for Osprey came on 9/27 with 44.
The decreased average in recent years is a surprising result,
since the Osprey is generally conceded to be still recovering (at least in some
areas) from reproductive failure in the 1950's through 70's as a result of DDT
poisoning. I have no explanation for this, except that since the decrease is a
fairly small one, it may simply be the result of random factors.
1st 9: 384.16 2nd: 336.04
Bald Eagle (Haliaeetus leucocephalus)
25 Bald Eagles were observed, on dates from 9/5 to
11/12. This is almost exactly the average for the last 8 years (25.23), and
considerably up from 16.87 for all 17. The highest number for Bald Eagle in a
day was 3, on both 9/ 6 and 9/ 25.
The Bald Eagle's recovery from DDT poisoning over the course
of the last 30 years is probably the best-known success story in ornithological
conservation, and numbers at Chestnut Ridge reflect this happy trend.
1st 9: 10.46 2nd: 25.20
Northern Harrier (Circus cyaneus)
90 Northern Harriers were recorded from 9/9 to
11/18, against an average of 115.70 (last 8) and 139.51 (last 17). The highest
day-total for harrier was 7, recorded both on 9/17 and on 10/20.
Harriers have a "slow-and-steady" migration, with
small numbers trickling by the watch from early 9/ into mid-November, with no
real peak. This species, like virtually all grassland species in the northeast,
has been declining in recent years. Our numbers over the years certainly reflect
this decline.
1st 9: 157.73 2nd: 112.86
Sharp-shinned Hawk (Accipiter striatus)
1,862 Sharp-shinned Hawks were recorded from 9/5
to 11/17, compared to averages of 1909.67 (last 8), and 2462.70 (last 17). Our
biggest Sharp-shin day was 10/8, when 195 were recorded. The decline of migrant
Sharp-shins at hawk lookouts across the Northeast has been widely noted. Several
different theories have been advanced to explain this, including possible
competition with the increasing Cooper's Hawk, a species that fills a somewhat
similar ecological niche, declining songbird (the Sharp-shin's principal food)
populations, and changing migration patterns. The changing migration pattern
theory is supported by recent large increases in the number of Sharp-shins
wintering to our north - the birds just may not be migrating as far south
anymore. Cooper's Hawks, however, which have been increasing as migrants in the
region, have also increased greatly as wintering birds in areas north of us. It
may be that the Cooper's Hawk has increased so much in recent years that even
with a similar change in migration patterns, there are so many more of them
around that we still see an increase in migrants (this increase has been noted
throughout the northeast- see the following species account). These accipiters
wintering farther north may be a result of recent global warming, or perhaps an
increase in bird feeders, which provide useful concentrations of smaller birds
for these bird-specialized raptors to prey on.
1st 9: 2886.01 2nd:1904.40
Cooper’s Hawk (Accipiter cooperii)
327 Cooper's Hawks were observed from 9/11 to
11/19, compared to averages of 283.73 (last 8) and 204.01 (last 17). Our highest
day total was 22, recorded on consecutive days, 10/11 and 12. This is another
species that seems to be recovering from the damage done by DDT, and indeed
Chestnut Ridge's yearly totals show a continuing dramatic, and heartening,
increase.
1st 9: 142.99 2nd: 288.51
Northern Goshawk (Accipiter gentilis)
15 Northern Goshawks were recorded, from 9/25 to
11/18. This is almost exactly the eight-year average (15.29), and not far from
the 17 year average of 13.26. The high for goshawk in a day was 2, on 9/25, 29
and 30, 10/7 and 11/7. As can be seen from the long-term numbers, this somewhat
irruptive species has continued to migrate past Chestnut Ridge in low but
seemingly stable (or perhaps slightly increasing) numbers over the years.
1st 9: 11.70 2nd: 15.25
Red-shouldered Hawk (Buteo lineatus)
84 Red-shouldered Hawks were observed, from 8/31
to 11/20. This compares to averages of 122.04 (last 8) and 106.00 (all 17). The
daily high for Red-shouldered was 17, on 10/23. There has been some concern that
Red-shouldered Hawks have been declining in the Northeast, but Chestnut Ridge's
numbers over the years have not reflected this, and in fact have shown a very
slight increase. Red-shouldered Hawks were affected somewhat by DDT, and they
apparently showed slight increases in some areas after it was banned. It is
possible that this may be interacting with other factors that may have caused
population declines in this species in the northeast (such as the draining of
wetlands and increased development) to produce this rather muddled picture of
its status.
Faherty (1997) points out that the Red-shouldered totals at
Chestnut Ridge over the years have tended to fluctuate strongly from year to
year, and speculates that this may be due to "a type of two year boom/bust
reproductive cycle." The yearly totals starting in 1983 go as follows: 87,
59, 188, 78, 147, 68, 147, 130, 81, 119, 51, 28, 169, 184, 148, 80, 203, and 84
this year. This is an interesting thought, and the three years since Faherty's
season in 1997 certainly have continued to exhibit this fluctuation. Then again,
as discussed earlier in the November summary, Red-shoulder migration might be
expected to be (and in fact from my limited observation seems to be) more
heavily weather-dependent than that of heavier raptors. Perhaps the variability
in the totals can be explained by differences in weather conditions from year to
year, and if this is true, we ought to be especially wary of postulating
population trends using our long-term data.
1st 9: 93.71 2nd: 117.84
Broad-winged Hawk (Buteo platyperus)
11,096 Broad-winged Hawks were recorded from 8/31
to 10/11. compared to averages of 6,497.81 for the last 8, and 7,785.07 for the
last 17. Our biggest Broad-wing day was 9/17, when a spectacular 4,110 went by
the lookout. How many Broad-wings we see at Chestnut Ridge seems heavily weather
dependent, with fewer recorded on days with very strong northwest winds. The
birds seem to be forced to migrate closer to the coast on days like these, when
hawkwatches nearer Long Island Sound tend to report much higher numbers than
usual. These vast fluctuations in the year to year totals make it hard to get a
handle on any possible population trends.
1st 9: 8770.38 2nd: 7006.10
Red-tailed Hawk (Buteo jamaicensis)
736 Red-tailed Hawks were observed from 9/5 to
11/20, which compares to averages of 605.74 (last 8) and 516.66 (last 17). The
highest Red-tail day was 11/2, with 77. The long term data show a moderate
increase in Red-tail numbers over the years, possibly due to an increase in edge
habitat in the northeast (so damaging to many species of forest-interior birds),
which this raptor favors for hunting.
1st 9: 448.47 2nd: 620.14
Rough-legged Hawk (Buteo lagopus)
1 Rough-legged Hawk was observed on 10/31, the only one recorded this entire
fall. This about on a par with previous years- usually only one or none is seen
over the course of a Chestnut Ridge season- Westchester county is just too far
south to get high numbers of this species, even in a good irruption year.
1st 9: 0.86 2nd: 0.77
Golden Eagle (Aquila chrysaetos)
4 Golden Eagles were observed, 2 on 10/17 and 2 on
11/7. This compares with averages of 7.95 (last 8) and 5.66 (last 17). This was
perhaps a bad year for Golden Eagle reproduction in eastern Canada, as many
hawkwatches in the Northeast reported unusually low numbers of this species this
fall. Still, though this year's 4 was way down from last year's 15, over the
years Chestnut Ridge's totals have shown a gradual increase in sightings of this
regal bird, which agrees with trends at many northeastern hawkwatches (though so
few are observed at this watch, caution is needed in drawing conclusions from
our data).
1st 9: 3.90 2nd: 7.52
American Kestrel (Falco sparverius)
538 American Kestrels were recorded, from 9/5 to
11/6. This compares with averages of 569.57 (last 8) and 607.30 (last 17). The
biggest kestrel day was 9/27, with 61. This small, elegant falcon has been
declining in the Northeast recently, and Chestnut Ridge's numbers seem to bear
this out. Reforestation of land that was previously in open fields (an important
part of kestrel habitat), a decline in the dead trees kestrels use for nest
sites, and recent development of much open land are all probable contributors to
this decline.
1st 9: 636.17 2nd: 566.08
Merlin (Falco columbarius)
42 Merlins were seen, from 9/2 to 11/7. This
compares with averages of 44.86 (last 8) and 37.51 (last 17). Our biggest day
for Merlin was 10/20, with 6. Merlins have increased somewhat at many other
northeastern hawkwatches in recent years, and Chestnut Ridge's long-term numbers
have shown this as well.
1st 9: 31.87 2nd: 44.55
Peregrine Falcon (Falco peregrinus)
16 Peregrine Falcons were observed, from 9/11 to
10/17, with a high of 3 on 10/3. This total is almost
the same as the 8-year average (15.04), and slightly above the 17-year average
(13.58). It is perhaps surprising that our numbers have not shown more of an
increase than this, given the Peregrine's reintroduction and extraordinary
recovery from the effects of DDT in the East (however, as with the Golden Eagle,
so few Peregrines migrate by this watch that its numbers are not really high
enough to make valid comparisons from year to year- migrating Peregrines are
much more numerous along the coast than at inland watches like Chestnut Ridge ).
1st 9: 12.46 2nd: 15.14
Unidentified Birds
Accipiter 123
Buteo 34
Falcon 17
Raptor/Vulture 51
Click for
Seasonal Summary
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