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1-15 January 2013

Installment #561---Visitor #Web Page Visitor Counter

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BLUE JAYS, Cyanocitta cristata:

Weather at Hilton Pond Center has been very mild thus far in the winter of 2012-13, with above-normal temperatures and below-average rainfall prevailing. Our always-anticipated cold-weather birds have not really arrived, giving us pitiful banding results for seasonal migrants 1 November through 15 January: Three Purple Finches, one Dark-eyed Junco, one Pine Siskin, three White-throated Sparrows, and two American Goldfinches. Were it not for trapping 81 House Finches--some of which actually might be local residents--we'd have almost nothing to show for our banding efforts over the past ten weeks or so.

In last week's installment we speculated about why last year's banding total was our lowest ever; some of the same reasons may help explain this winter's paucity of birds. We're not doing anything particularly different this year--save one thing: Along with the usual black sunflower and thistle seeds in feeders, we've been ground-scattering a mix of millet, milo, and cracked corn. What has been missing is another additive we've always used in the past--shell corn--dry whole kernels relished by some of the larger birds (and squirrels). This week at Hilton Pond Center we finally added shell corn to our mid-winter scatter mix and, believe it or not, within five minutes we had trapped our first Blue Jay in two years!

All text, charts & photos © Hilton Pond Center

We're always pleased to have a Blue Jay in-hand, if only because it brings back happy memories. Before we made the leap to conducting field research on hummingbirds, Blue Jays were our study species during grad school days at the University of Minnesota. There, mostly at the university's Cedar Creek Natural History Area north of the Twin Cities, we spent three very long, very cold, very dark winters--and some buggy springs and summers--working on the behavioral ecology of Blue Jays. Our advisor was the late Dr. Harrison "Bud" Tordoff--esteemed ornithologist and past president of the American Ornithologists' Union. Bud (at right with a banded Peregrine Falcon about to be released) wasn't very keen on our thesis topic, in part because his former grad students had failed miserably in efforts to find enough Blue Jay nests to provide new insights on the species' breeding and non-nesting behavior. Bud actually wagered a hundred bucks at the beginning of our first field season we'd not be able to find more than ten jay nests--an insufficient number to draw conclusions worthy of publication. Not willing to ignore a wager or a challenge, we trundled off into the oak savannahs of central Minnesota in the spring of 1979, looking for Blue Jays and their nests.

In one of those strokes of serendipity that often allows success in field projects, we met soon bird bander Jean Vesall, who also was interested in Blue Jays AND happened to live in a subdivision that adjoined Cedar Creek. With the help of Jean and her husband Dave--plus hyper-energetic chickadee expert Jim Howitz and several undergrad volunteer assistants--we prowled Cedar Creek's oak savannah and the subdivision. That first year in a relatively small area of about 120 acres the team located more than 100 jay nests! Not all were active at one time; some were abandoned due to competition or predation, while others may have been "practice nests" by newly established breeding pairs. In each of the following two seasons we found even more nests that represented what was apparently the highest nesting density ever described for the species. (NOTE: Bud Tordoff never paid up on his bet, but he did finally admit he had been wrong to doubt our industriousness and productivity at finding Blue Jay nests!)

All text, charts & photos © Hilton Pond Center

On top of nest-hunting (and subsequent banding of Blue Jay nestlings during the breeding season), we spent a lot of time year-round trapping and mist netting jays. Each received the usual numbered aluminum band issued by the federal Bird Banding Laboratory, but we also gave each bird three color bands in a unique combination that allowed us to identify each bird without recapture--simply by looking at its legs through binoculars or a spotting scope. (In the photo above, one about-to-fledge jay shows a yellow-over-orange combination on its right leg while its two less-adventurous nestmates hunker down.) In all we color-marked more than 1,500 nestlings, fledglings, and adults during the three-year study and discovered numerous pairs of Blue Jays maintained year-round bonds; those that did got a much earlier start on breeding each spring. Established pairs also frequently showed strong site fidelity, often nesting in the very same site or close to it year to year. And curiously, the most successful nests were those built within the subdivision, especially on human structures such as houses--or on limbs hanging over dog pens! (We suspect these human-related locales served to minimize predation by egg-robbers such as crows, snakes, and squirrels.) We uncovered many more interesting factoids about Blue Jays during those grad school days--certainly enough to give us more admiration and respect for the species than admitted to by many backyard birders.

All text, charts & photos © Hilton Pond Center

When we returned from Minnesota in 1982 to establish what is now Hilton Pond Center we hoped to continue our work with Blue Jays and caught 208 of them locally during our first seven years here (see chart above). We dutifully color-banded these individuals--some of which most certainly were winter migrants--but only found a few nests. Alas, in the mid-1990s the Blue Jay population crashed--in part because a neighboring farmer clear-cut a 70-acre Loblolly Pine forest and then because West Nile Virus took a major toll on jays and other corvids across the eastern U.S. It's a good thing we had already shifted to Ruby-throated Hummingbirds as our species of interest; in the past 15 years we've averaged less than a dozen or so Blue Jays per calendar year and in 2012 ended up with none--hardly enough jays to derive any new knowledge of scientific significance. With all this in mind, one can understand our delight this week at the Center's first in-hand Blue Jay since January 2011. For old-time's sake, we took a lot of photos of this bird and include them below in an effort to give folks better appreciation for an under-appreciated species.

All text, charts & photos © Hilton Pond Center

Blue Jays are sizable birds, bigger than an American Robin and smaller than Mourning Dove. Tail tip to bill tip they measure 9"-12", with a substantial wingspan of 13"-17". Individuals from Canada can be up to 25% larger than those that breed in Gulf Coast states. (Some taxonomists recognize up to four subspecies of Blue Jays, based on size, plumage, and distribution.) Since northern populations often migrate, the Carolina Piedmont plays host to migrants as well as non-migratory residents--providing a mix of "big" and "small" individuals at the winter feeder. Blue Jays are sexually monomorphic, i.e., males and females look alike externally. Despite extensive measurements on our Minnesota jays we were never able to find a way to sex them based on mass or length of wing, tail, leg or bill. The only sure way to sex a Blue Jay (short of surgery) is during the breeding season when females develop a prominent brood patch--a bare patch of edematous and vascularized skin on the belly that enhances transfer of body heat to eggs and chicks.

All text, charts & photos © Hilton Pond Center

Although sexing Blue Jays is very difficult, it's often possible to determine the age of an individual jay--or at least to say whether it's "immature" or an "adult." Younger birds retain their juvenal feathers--particularly alulars and secondary coverts. In the image above, the main flight feathers (white-edged primaries at the bottom of the photo) are overlapped by bluish-brown primary coverts; similarly colored alular feathers at the bend of the wing overlap some of the primary coverts. Compare all these with the white-tipped, blue secondary coverts that are heavily barred with black. This noticeable contrast between primary and secondary coverts is the sign of a younger bird, meaning the jay we caught this week (in January) is in its second year; that is, it hatched sometime during the summer of 2012. Older Blue Jays (after second year) never have brownish primary coverts or alulars; these feathers are blue and almost always have some degree of barring. In many jays this plumage difference allows you through binoculars to age a mid-winter bird at your backyard feeder.

All text, charts & photos © Hilton Pond Center

The Blue Jay's genus name, Cyanocitta, comes from Latin and Greek words meaning "blue" and "chattering bird," while the species epithet cristata refers to the jay's crest--a structure that often lies flat. These terms are mostly accurate, except for the blue part, for in actuality Blue Jays appear but are not "blue"--they are black and white and gray. We say this because Blue Jays--as well as Indigo Buntings, Blue Grosbeaks, Black-throated Blue Warblers, and Eastern Bluebirds--do not get their color from blue pigment. Their blue appearance is caused by tiny air bubbles and grooves in feathers that overlay the black pigment, melanin. When light strikes the bubbles and grooves it is scattered such that the observer only perceives blue wavelengths--the same phenomenon that makes the black of space look blue when sunlight is scattered by Earth's atmosphere. Thus, the blue color of a Blue Jay is structural in nature rather than pigmental, unlike the way a Northern Cardinal appears red because its feathers contain red pigment. One of the remarkable things about Blue Jays is how many different shades of "blue" they exhibit--as in the photo above of the bird's back and crossed wings--indicating there are many different configurations of air bubbles and grooves overlaying the melanin. Where melanin pigment is completely absent, of course, the feathers appear white.

All text, charts & photos © Hilton Pond Center

And while we're on the topic of color, although from a distance the Blue Jay appears to have a large black eye, its iris is actually rich, deep chestnut--or at least appears to be. As with its plumage, the jay's iris color comes from scattering of light, this time because of varying concentrations of melanin crystals that occur in various structures within the eye. (From this you may conclude correctly that if you have blue or hazel or green eyes they aren't really hazel, green, or blue. No to burst the poet's bubble, but we humans all have black eyes--unless we're true albinos who lack melanin completely.)

All text, charts & photos © Hilton Pond Center

It's interesting that the whole time we had this week's Blue Jay in hand--including measurements, banding, and photography--it never disgorged that shell corn in its craw. We could see two kernels for sure, but based upon the distended crop (see photo above), there were probably more than that, and our captive wasn't about to give up ANY of them. Blue Jays are hearty eaters--one reason why some folks don't like them much--and a small flock of jays can clean out a bird feeder in short order. They're pretty much omnivorous, eating lots of insects during warm weather and then shifting to fruits, nuts, and seeds as seasons dictate. Blue Jays have what we believe is an undeserved reputation for robbing other birds' nests of eggs and chicks--several studies showed their stomachs contained less than one per cent of these items--but they sometimes do it and occasionally even take an adult bird. Much more important is this information: The Blue Jay often caches seeds, burying them and then forgetting where some of them lie.

All text, charts & photos © Hilton Pond Center

And we don't just mean they cache sunflower seeds, either. In Minnesota we frequently saw Blue Jays gather two, three, or even four red oak acorns in their crops and fly considerable distances before alighting to eat. They almost never consumed all four nuts, choosing instead to scratch out a small hole in the ground in which to hoard one or more acorn. These jays thereby did the mighty oak a mighty favor, transporting its acorns much further than they would be taken by a terrestrial mammal such as squirrel or chipmunk. In this way, Blue Jays play a very important role in disseminating the genes of oaks, and of expanding the hardwood forests of which these trees are an integral part. Here in the south I've even seen a Blue Jay stuff an entire unshelled Pecan in its mouth and take off for who knows where, thus insuring the Pecan's offspring has a chance to sprout and flourish far from the mother tree.

We could go on and on about Blue Jays, but next time you see one at your backyard feeder, try to refrain from tapping on the glass and shooing it away. Jays may seem boisterous and gluttonous, but this common backyard species eats much larger insect pests than most birds can consume, it helps expand North American forests, and it entertains us with its highly social behavior. Even its vocalizations are pleasing to the ear, from its familiar "jay-jay-jay" call to its very accurate imitation of a Red-shouldered Hawk. If you happen to be in the Carolinas, spend some time just watching these colorful corvids, happy in the knowledge you didn't have to endure three very long, very cold, very dark winters with us in the wilds of Minnesota studying the behavioral ecology of Blue Jays!

All text, charts & photos © Hilton Pond Center

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1-15 January 2013

American Goldfinch--2
Northern Cardinal--2
White-throated Sparrow--3
House Finch--26
Purple Finch--1
Red-bellied Woodpecker--1
Blue Jay--1
Mourning Dove--3

* = New species for 2013

8 species
39 individuals

8 species

39 individuals

(since 28 June 1982, during which time 171 species have been observed on or over the property)
126 species (32-yr avg = 65.2)
58,210 individuals
(32-yr avg = 1,819)

(with original banding date, sex, and current age):
Northern Cardinal (8)
08/17/09--5th year female
09/27/11--3rd year female
10/05/11--3rd year male
04/16/12--after 2nd year female
08/27/12--2nd year male
09/09/12--2nd year male
09/10/12--2nd year male
09/21/12--2nd year female

--The first banded bird on 1 Jan 2013 was an adult male Mourning Dove with rosy breast, slaty crown, iridescent neck spot, and blue eye shadow--a colorful way to start our 32nd year of banding at Hilton Pond Center!

--A couple of weeks ago the Center's photo essay dealt with effects of our on-going Piedmont drought. We included an image of an Eastern Elliptio clam with unusual holes in its shell. After that posting we heard from several experts who have a likely explanation for those holes. To read what the malacologists said, scroll down to the newly added "Postscript" at the end of installment #557 at The Shrinking Pond.

--A temperature of 74 degrees on 13 Jan--as indicated by the Center's digital weather station--was probably very close to a all-time record high for the date. (The average daytime high for the month is 53, with a January record of 80.)

--The Center's Yearly Yard List 2013 of birds seen on or over the property stands at 24 species as of 15 Jan.

--Last week's photo essay was an easily digestible summary with eye-pleasing photos of the 2012 Bird Banding Season at Hilton Pond. It's archived and always available as Installment #560.

All text & photos © Hilton Pond Center

Oct 15 to Mar 15:
East of the Rockies please report your sightings of
Vagrant & Winter Hummingbirds

(immature male Rufous Hummingbird at right)

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Hilton Pond Center for Piedmont Natural History is a non-profit research, conservation & education organization in York, South Carolina USA; phone (803) 684-5852. Directed by Bill Hilton Jr., aka "The Piedmont Naturalist," it is parent organization for Operation RubyThroat. Web site contents--including text and photos--may NOT be duplicated, modified, or used in any way except with express written permission of Hilton Pond Center. All rights reserved worldwide. To request permission for use or for further assistance, please contact Webmaster.

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