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Spring 2007
Notes and Highlights for
May 29-June 3
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here for This Week's Totals
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here for Season Totals
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During the final full week of the
2007 spring banding season at Powdermill, we banded just 127 birds of 32
species (including, however, one exciting new species for the season) and
processed 48 recaptures, with a total effort of 1,165 net-hours (giving
a very low capture rate of just 11 new birds per 100 net-hours).
Our banding total did not exceed 30 birds on any day this week, and our
species diversity maxed out at just 15. By comparison, the
best single banding day this spring (only a couple weeks ago on May
17) netted us 170 new birds of 40 species!
The shape of spring migration
(plotted in the graph below), with its gradual build-up to a peak in number
and variety of birds over the course of 10 weeks, followed by a rapid decline
in banding and species totals in just two weeks time, resembles an exciting
roller-coaster ride!
The top five species this week were
Cedar Waxwing (35 banded), Gray Catbird (16), Red-eyed Vireo (12), Acadian
Flycatcher (6), with American Goldfinch, "Traill's" (i.e., Alder and Willow)
Flycatcher, and Ruby-throated Hummingbird tied for fifth place with five
of each banded. Our overall total for spring 2007 was 2,822 birds
of 102 species banded, both of which statistics are very close to the long-term
averages at Powdermill of 2,764 and 97.
Our thanks to Pam Ferkett, Mary
Shidel, Michael Allen, Bob Leberman, Danilo Mejila, Maria Paulino, and
Brent Worls for their help with the banding this week.
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Not surprisingly, the past week
of banding bridged the always blurry boundary between the migration and
breeding seasons at Powdermill. This was evidenced by the capture
of non-breeding species, like Yellow-bellied Flycatcher, that clearly belong
in the former category...
The spread wing pictured below belonged
to a second-year (SY) YBFL banded on 6/1.
Note the eccentric molt limit between the
block of six brownish retained juvenal outer secondaries
and inner primaries and the surrounding dark
dusky-gray molted inner secondaries and outer primaries
(look also at the difference in the brownish
vs. blackish feather shafts between the retained and molted flight feathers).
and an HY House Finch, equally
clearly a product of the latter!
Banded on 6/3, this immature House Finch
(the sex of this species is unknown in its
juvenal plumage)
is our first HY bird of the year.
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Two warblers banded on 5/29 showed
how variable the condition of feathers can be when birds return to their
breeding grounds in spring. This is a product of how much prealternate
body molt a bird has undergone, as well as how physically abrasive the
environment was where a bird overwintered. The ASY male Kentucky
Warbler (top photo) was in very fresh plumage, while the SY female Black-throated
Green Warbler banded on the same day was exceedingly worn.
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On the last day of the week, we
banded an SY female Blue-winged Warbler. All the wablers in the genus
Vermivora
are, to one degree or another, specialized "branch-tip" foragers with the
ability to use their thin sharp beaks to pry open and into terminal buds,
leaves, and flowers in search of small insects. When we band these
species, we often demonstrate the interesting bill opening action by having
a visitor use their fingers to try and lightly close one of these bird's
bills. Almost invariably, the warblers will respond by trying to
pry the fingers apart! It's one of our favorite "stupid bird tricks!"
Interestingly, this unique, reverse-opening bill action also is shared
with orioles (see previous
post on this).
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For the most part, visitors have
to take our word for it when we explain that this unusual "a-bill-ity"
of Vermivora warblers actually is a unique feeding adaptation.
So, I was as thrilled as the photographer herself when I came across this
entry and photo in the wonderful (engaging, entertaining, and educational!)
blog of nature artist, writer, and photographer, Julie Zickefoose.
Click on the screenshot below to link to Julie's website (which I
guarantee you'll then want to add to your "favorites").
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This photo of an especially colorful
SY male American Redstart banded on 6/2 shows an adaptation related to
this species' specialized aerial foraging behavior. In all likelihood,
the specialized feathers at the base of its bill, called rictal bristles,
function like "eyelashes" to keep possibly harmful airborne detritus (e.g.,
wing scales of moths and butterflies; chitinous appendages of flying beetles
and bugs) from getting into its eyes when it makes its mid-air strikes
to catch an insect. Not surprisingly, this effective and important
protective adaptation has evolved independently in a number of lineages
of "flycatching" birds, including the true flycatchers (see bottom photo
in the series of Alder/Willow flycatchers below) and nightjars (like Whip-poor-will).
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Speaking of flycatchers, we had
an unusual opportunity to compare and contrast two obviously very different
"Traill's" Flycatchers banded on 6/1. Although we were a little too
busy to measure out the wing formulas of the two birds, which can sometimes
help to distinguish the very cryptic Alder and Willow flycatchers (Pyle
1997), the following outwardly visible criteria suggested that we did,
in fact, have one of each species in hand. In the series of photo
below, the presumed Alder is on the bird on the right or in the photo below.
First, the lores of one flycatcher,
the putative Alder, definitely were much lighter, and the dorsal plumage
of that bird was distinctly greenish. This contrasted with the putative
Willow, which was grayer above and did not have conspicuous light-colored
lores. The wing bars and tertial edgings of the presumed Alder were
perhaps slightly broader and brighter than the bird we believed was a Willow,
but this difference was subtle at best. One trait among those given in
Pyle (1997) that did not agree at all with our identification of the two
birds, however, was crown spotting: the Alder should have had larger,
more distinct crown spots compared to the Willow, but this was not the
case (see bottom photo below; the probable Alder in on the right).
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We banded two second year (SY) American
Goldfinches on 6/2. Both were unusually bright and colorful for young
birds of their sex. Compare the SY female (top bird in the photo
below) with what we called an unusually dark ASY
female a couple of weeks ago. The male-like plumage of the SY
female would have made for an even more surprising comparison if we'd had
a more typical, duller SY male to pose with her.
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Last but not least, we banded a
new species for the spring season on 6/1--a an adult (ATY) male Pileated
Woodpecker. Although we banded a Pileated Woodpecker last spring,
too, more often than not we miss catching and banding this species in any
given banding year. When banding volunteer, Mary Shidel returned
to the banding lab with her prize, she found a very appreciative audience
of 5th graders from the Pittsburgh Urban Christian School (PUCS) on hand
to share the occasion. The day before, Bob Mulvihill had given a
program about birds, bird watching, bird research, and bird conservation
to the entire group of about 125 students, teachers, and parents of K-5th
graders from PUC, who were spending a couple of days at the Ligonier Camp
and Conference Center about ten miles away from Powdermill. A follow-up
visit to Powdermill was reserved for the older students.
The photos below (clockwise
from left) show Bob Mulvihill banding the PIWO (the species takes a band
size 4), weighing it in the same weighing cone that is used for all other
birds banded at Powdermill, including hummingbirds(!), and holding the
PIWO up to show visiting 5th grade students, teachers, and parents from
PUCS. Puppy, as always, tries to steal a little bit of the show!
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Everyone stood back and watched
as the PIWO was released out the front door of the lab after banding.
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Of course, the Pileated was just
one of several birds we had on hand for our visitors from PUCS.
In the photo below, taken from the outside in (it was a little too crowded
"in" for picture taking!), Bob Mulvihill shows the group the waxy red feather
appendages that give a Cedar Waxwing its name.
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The approaching summer notwithstanding,
early morning temperatures on 5/31 were very cool (just under 50°F),
and an adult male Ruby-throated Hummingbird caught in a net on the first
round of the morning showed the conspicuous signs of hypothermia, or torpor--i.e.,
fluffed plumage, closed eyes, and a flared gorget (see photos below).
As we have explained before on this website, male RTHUs can become energetically
very stressed, even in summer, because of their very small size.
Many, if not most male RTHUs engage in an adaptive lowering of their metabolism
(i.e., torpor) overnight in order to conserve energy for the inevitable
overnight fast. The strategy works fine as long as enough stored
energy is left to enable the bird to rouse to activity the following morning.
If so, then finding food right away becomes a very high priority.
Anything that delays or prevents this, such as cold or rainy weather (or
getting caught in a mist net), can have serious energetic consequences
for male hummingbirds. For the most part, females are spared this
energy crisis because they are significantly larger than males, lose less
body heat through their proportionately smaller surface area, and have
a lower per gram metabolic rate.
For warm-blooded animals,
2.5 grams is something of a physiological threshhold for maintaining homeothermy
(i.e., a constant body temperature). It came as no surprise, therefore,
when we put this RTHU male on the scale to find that it weighed exactly
2.5 grams. Mulvihill et al. 1992 (A
possible relationship between reversed sexual size dimorphism and reduced
male survivorship in the Ruby-throated Hummingbird; Condor
94:480-489) showed with an analysis of Powdermill
RTHU banding data that males have a significantly lower survival rate and
maximum life span (3-4 vs. 7-9 yrs) than females because of their small
size.
Fortunately for the torpid male
RTHU caught on the morning of 5/31, the energy crisis it faced after being
caught in our net was quickly reversible. Give them a number of sips
of sugar water, a little time to rev up their metabolism, and males like
this one are good to go again!
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Last Updated on 06/05/2007
By Robert S. Mulvihill and Molly
McDermott