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Now
You See Them, Now You Don't
By WESLEY M. HOCHACHKA
Where, when, and why the birds didn't show up
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FeederWatch Annual Report
In each Annual Report, we use FeederWatch data to give us insights
on a timely topic and share the year's top-10 lists for each
FeederWatch region.
Last year was record-breaking for Project FeederWatch, both
in terms of participation (16,641 participants) and online
data entry (60 percent of those who submitted data). Online
submissions have helped us to analyze data more quickly than
ever.
The new FeederWatch season begins November 9, 2002. Sign
up or renew today. Click here
for contact information.
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The poet who penned the phrase, "absence makes the heart grow
fonder," clearly was not a Feeder-Watcher. When I don't see "my"
birds in a FeederWatch count period, my feelings turn toward curiosity
(where could they be?), and self-doubt (did I watch my feeders closely
enough this week?).
It's inevitable that every Feeder-Watcher will miss seeing some
birds during a count. No matter how diligent you are, you can only
watch your feeder during a fraction of the day-and sometimes that
happens to be the fraction when your birds aren't there. It's also
impossible to keep your eyes focused on your feeders continuously,
and it can take just a few seconds for a bird like a nuthatch to
grab a seed and disappear.
But birds also spend varying amounts of time at your
feeders from week to week and even year to year. Our analysis of
last winter's FeederWatch data shows that your feeder birds may
be spending a great deal of time at other sources of food nearby
or migrating in or out of your region at some point during the FeederWatch
season (November to April). The data also show that some birds,
such as irruptive species, may not have appeared at all last year,
simply because they were spending the winter elsewhere.
Why don't I see all of "my" birds
every week?
Some birds may visit your feeder infrequently because they can find
other sources of food nearby. But their energy needs increase during
cold weather, and food can be hard to find during winter. So intuitively,
we might expect to find birds at feeders most often during winter's
coldest months and in regions with the coldest climates.
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Downy Woodpecker
Steve Leaton |
To investigate this possibility, we started with the 2001-2002 FeederWatch
data for three widespread species with contrasting habits. The Downy
Woodpecker is mostly sedentary, inhabiting the same local area year-round.
The Red-breasted Nuthatch is an irruptive species whose winter range
varies from year to year. The Sharp-shinned Hawk, migratory in some
regions, is a predator that may hunt for smaller birds attracted to
feeders.
Ideally, we wanted to be able to track the comings and goings of one
bird at a time, which would make it easier to estimate just how much
more frequently a single bird visited a feeder in midwinter than in
early winter or spring. We started by narrowing the observations to
those submitted by FeederWatchers who reported seeing at most only
one Downy Woodpecker, Red-breasted Nuthatch, or Sharp-shinned Hawk
during a count period, in more than one period. This left us with
information from between 900 and 1,500 observers per species. We assumed
that any changes in reporting reflected changes in the birds' behavior
rather than changes in the observers' viewing habits.
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| Figure 1: Probability that a
Downy Woodpecker was reported at different times during the
2001-2002 FeederWatch season. Downy Woodpeckers did not necessarily
use feeders most often during the middle of winter or in the
coldest regions. The analysis only included data from FeederWatchers
who saw at most one Downy Woodpecker, on more than one count
day. (Note: we did not receive enough reports to make a rigorous
analysis of the Al-Can region.) |
In colder climates, did FeederWatchers see birds at feeders more
often? Not necessarily. For example, FeederWatchers spotted Downy
Woodpeckers at feeders most often in the North Atlantic and Mid-Central
regions, followed by the East-Central and Southeast regions (Figure
1). Although three of these regions can be cold and snowy, the same
can rarely be said for the Southeast.
Although the regional rankings differed for Red-breasted Nuthatch
(Figure 2) and Sharp-shinned Hawk (Figure 3), the same story emerged:
FeederWatchers in the coldest regions weren't necessarily treated
to more bird sightings.
There was also no clear trend that Downy Woodpeckers were reported
at feeders most often during midwinter. Only about half of the regions
showed a midwinter peak, but these peaks were not pronounced. FeederWatchers
from the North Central region saw Downy Woodpeckers only 15 percent
more often in January than November. For the other regions, these
differences were even smaller. Red-breasted Nuthatches and Sharp-shinned
Hawks showed no midwinter peaks in feeder visitation at all.
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| Figure 2: Probability of reporting
a Red-breasted Nuthatch at different times during the 2001-2002
FeederWatch season. Several of the sharpest seasonal declines
in nuthatch sightings occurred in regions distant from the nuthatch's
northerly or mountainous breeding grounds, as might be expected
for birds starting their northern migrations early. The analysis
only included data from FeederWatchers who saw at most one Red-breasted
Nuthatch on more than one count day. (Note: we did not receive
enough reports to make a rigorous analysis of the Al-Can region.) |
Would we have noticed greater differences in seasonal feeder use if
last year's winter had been more severe? Would we have come to a different
conclusion if we had looked at actual temperatures instead of assuming
that midwinter would be the coldest time? Only further work will tell,
but clearly other factors besides general seasonal changes in climate
must influence whether a bird turns up at a feeder.
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Red-breasted Nuthatch
L. McGlothlin
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For example, many of you saw Red-breasted Nuthatches less often as
the winter wore on, perhaps because of migratory movement and/or winter
mortality.
With few exceptions, several of the sharpest seasonal declines in
nuthatch sightings occurred in regions distant from the Red-breasted
Nuthatch's northerly or mountainous breeding grounds. Such a pattern
may reflect early northward migrations of nuthatches from these areas.
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Sharp-shinned Hawk
Don Fitzgerald |
Migratory movement may also explain why Sharp-shinned Hawk sightings
increased in some regions but decreased in others (Figure 3). FeederWatchers
in northerly regions were most likely to see sharp-shins early in
the season, but those in some southerly regions were more likely to
see sharp-shins later. This pattern is consistent with the southward
winter migration of Sharp-shinned Hawks.
Where were the irruptive species last winter?
In past FeederWatch reports we've talked about the nature of some
birds' irruptive migrations, which typically occur every other year
(Birdscope, Autumn 2000; Birdscope, Autumn 2001). However, we're
never certain which species will appear where or how abundant they
will be.
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| Figure 3: Probability of reporting
a Sharp-shinned Hawk at different times during the 2001-2002
FeederWatch season. Note that reports of sharp-shins declined
through the season in northerly regions, but increased in some
southerly regions. The analysis only included data from FeederWatchers
who saw at most one Sharp-shinned Hawk on more than one count
day. Increases in reporting rates over time may reflect visits
by different sharp-shins. (Note: we did not receive enough reports
to make a rigorous analysis of the Al-Can region.) |
To look at last winter's irruptive migration, we summarized 14 years
of FeederWatch data for the four most widespread irruptive species:
Red-breasted Nuthatch, Pine Siskin, Common Redpoll, and Evening Grosbeak
(Figure 4). Of these, the Red-breasted Nuthatch was the single most
widespread irruptive species this year. Evening Grosbeaks were just
plain absent from feeders everywhere.
FeederWatchers in some regions wondered where any of the "common"
irruptives were. In the East, we expected to see a substantial irruptive
migration last year. But if you live south of the Canadian border
and well east of the Rocky Mountains, it's likely that some anticipated
feeder visitors, such as Pine Siskins and Evening Grosbeaks, never
showed up. Put simply, it looks like there was sufficient natural
food last winter in these regions to keep many potential irruptive
migrants closer to their summer homes than in years with more dramatic
irruptive migrations.
In contrast, the Northern Rockies, Great Lakes, and North Atlantic
regions all had their best-ever showing of Red-breasted Nuthatches
last winter.
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| A Clay-colured Robin in Jemez
Springs, New Mexico, a first state record. Photographed by R. |
Likewise, Common Redpolls had banner years in the Al-Can and Northern
Rockies regions. FeederWatcher Brian Carrigan of Blackfoot, Idaho,
reported hearing from birders all around Idaho last winter who were
seeing redpolls in their communities for the first time in 15 years.
But FeederWatchers in regions farther south and east reported average
or below- average redpoll numbers.
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| Many warblers lingered in the North Atlantic
region, including this Wilson's Warbler photographed in Halifax,
Nova Scotia, by S. Borkowski. |
Pine Siskins were very much a western mountain phenomenon,
with record or near record showings in the Northern Rockies, North
Pacific, and Southwest regions. "On the weekend of January 5-6
my feeder site was inundated with Pine Siskins," reported Diane
Yusko Fielding of Campbell River, British Columbia. "They numbered
nearly 100 at several times . . . the most Pine Siskins I have ever
seen at my site."
FeederWatch data show the big picture
When we don't see the birds we expect at our feeders, it can leave
us feeling a bit perplexed. By combining your observations with those
of other FeederWatchers, we can show what the absent birds were up
to, be it visiting other local food sources or visiting entirely different
parts of the continent. The beauty of data from Project FeederWatch
is that they allow us to distinguish between absences that reflect
widespread population declines and absences that reflect normal variations
in feeder use and the migratory movements of birds within and between
years.
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To view regional top-10 lists and
Rare Bird Highlights, click on the gray dots above.
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Suggested
citation: Hochachka, Wesley M. Now You See Them, Now You Don't.
Birdscope, newsletter of the Cornell Lab of Ornithology,
Autumn 2002. <www.birds.cornell.edu>
For permission to reprint all or
part of this article, please contact Miyoko Chu, Editor, Cornell
Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, New York. Phone
(607) 254-2451. Email mcc37@cornell.edu
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