GENERAL INFO

CONTENTS

RESEARCH

EDUCATION

PUBLICATIONS

MISCELLANY

UPCOMING OPPORTUNITY:
Join us for another
Winter Hummingbird Expedition to Costa Rica
in November/December 2005 or February 2006

MORE AND MORE BLUEBIRDS;
THIS TIME, ADULTS

After revealing last week that our mystery bird at Hilton Pond Center was a just-fledged Eastern Bluebird, we weren't surprised in recent days to observe two adult bluebirds--individuals that could be the parents of our now-illustrious juvenile. This week we've seen three spot-breasted youngsters and a pair of adults washing up in the bird bath just outside our office window, and the quintet appears to be a family unit. Of these five, only the fledgling from last week was banded, so we were pleased on 8 June when the two adult bluebirds became ensnared in a mist net near the bath. The female hit our net first with the male blundering in several seconds later--perhaps in an unsuccessful attempt to rescue his mate from her predicament. We quickly went out to remove the two from the net and worked first with the female (below), just in case she might be tending to a new set of eggs.

All text & photos © Hilton Pond Center

As we removed the female bluebird from mesh draped softly around her head and wings, our prediction she was reproductively active soon held true: Blowing on her belly feathers (below) revealed one of those well-developed "brood patches" we typically see on songbirds this time of year. The brood patch--devoid of feathers, infused with blood vessels, and with bare skin underlaid by a soft cushion of watery fluid--provides an ideal mechanism for transmitting the mother's body heat to eggs or chicks. In most passerine birds the brood patch occurs only in females--the male Great-crested Flycatcher is one exception--but well-developed patches ARE found in male woodpeckers and some other non-songbird species.

Although most people will never get to see an actual brood patch in-hand, they usually have no trouble identifying a free-flying Eastern Bluebird, Sialia sialis--especially if it's an adult male (below). His bright blue back, head, wings, and tail can be breathtaking--especially in bright sunlight when his plumage takes on its deepest hue.

The dorsum of the female (below) is also blue, but she sports blue-gray feathers rather than the male's bright azure. As is often the case in songbird species, the female bluebird is drabber than her mate--the conventional wisdom for such dimorphism being the female needs to be less conspicuous when sitting on eggs or chicks. Such logic won't work for bluebirds, however, since the female incubates and broods in the darkness of an old woodpecker hole or wooden nest box, so perhaps there's another explanation.

Folks are aware that a bluebird is mostly blue, but some are surprised when they realize adult bluebirds of both sexes have an orange breast, that of the male (below) being somewhat more intense. We guess the male netted this week was probably a second-year bird, since his feathers were scruffy and worn and a little less brilliant than what we've seen in older males we've recaptured. In the photo below, the missing patch of feathers on his upper breast may have come out during a territorial battle.

Here at Hilton Pond Center the Eastern Bluebird population has declined over the past 23 years, primarily because our once-open 11 acres is now young woodland. Bluebird nest boxes we built and erected on poles and trees are occupied instead by cover-loving Carolina Chickadees, Eastern Tufted Titmice, Carolina Wrens, Southern Flying Squirrels, and hordes of Organpipe Mud Dauber wasps; only those few boxes facing an open field adjoining the Center still attract the attention of breeding bluebird. In fact, we suspect the bluebird family we've been observing these past few weeks nested in an old woodpecker hole somewhere above our subcanopy of Flowering Dogwoods and Eastern Redbuds, but they could have come from neighboring farmland kept open for cattle grazing.

It's likely the female bluebird we caught this week was already on her second clutch of eggs for the year. Eastern Bluebird pairs whose nest boxes we monitor in the Carolinas often double- or even triple-brood, with the clutch size usually dropping from 5-6 to 3-4 to 2-3 as the season progresses. Young from the initial broods often serve as "helpers at the nest," bringing tasty food morsels to their younger siblings. Interestingly, researchers have found that a female Eastern Bluebird frequently mates with multiple males so that one or more chicks in a given nest may be only a half-sibling to its nestmates--which certainly dispels the idyllic image folks have of devoted bluebird pairs tending to their young. Sometimes the male bluebird also wanders, copulating with more than one female, and to really confuse the question of "Are they 'his, mine, or ours'?", female bluebirds sometimes "dump" an egg, laying it in someone else's nest box for a completely unrelated bluebird pair to incubate, brood, and raise. Monogamy does occur, of course, but among enterprising Eastern Bluebirds we can never rule out polyandry (mating with more than one male) or polygyny (mating with multiple females).

Despite such diverse breeding strategies, Eastern Bluebirds--and their more westerly counterparts, the Mountain Bluebird (Sialia currucoides) and Western Bluebird (S. mexicana)--suffered from precipitous population declines by the mid-20th century, primarily because natural cavities disappeared as farmers and developers cut down America's forests and/or eliminated vegetational "edges" preferred by bluebirds. Thanks to artificial nest boxes (above right) and a new philosophy of NOT felling dead trees, all three species are recovering nicely across their respective ranges. Leading the way toward understanding bluebird needs and providing habitats and nesting sites for them is the North American Bluebird Society (logo at left), which we were honored to address at their national meeting in mid-May in Asheville NC. NABS was hosted by the North Carolina Bluebird Society--one of the most active of its state affiliates--whose helpful coordinators are located in many of North Carolina's 100 counties. South Carolina unfortunately has no state-wide bluebird group, despite our occasional efforts through Hilton Pond Center to drum up interest.

Plenty of Palmetto State individuals ARE interested in bluebirds, however, as is evidenced by the proliferation of nest boxes in backyards and along our highways and byways and beneath power line rights-of-way. If you want to attract bluebirds to your own "back forty," check out the North American Bluebird Society, or review our guidelines for Attracting Bluebirds on this Web site for Hilton Pond Center. Although it's already mid-June, it still may not be too late to entice a late-breeding pair this year, so follow our instructions on how to make, hang, and maintain a bluebird nest box. In the right habitat and with a little bit of luck you, too, can help assure the world is blessed with more and more bluebirds.

All text & photos © Hilton Pond Center