Archive for May, 2008

How Does a Brown-headed Cowbird Know It’s a Cowbird?

Saturday, May 31st, 2008

For the past several days, the whistle and jingle of a pair of Brown-headed Cowbirds has been common around our yard, and I’ve seen the pair several times, including at the birdbath. They’re an unwelcome presence, and their dark coloring – the males are black with brown heads – encourages me to think of them as sinister. But there’s one question about Brown-headed Cowbirds that intrigues me.

Brown-headed Cowbirds are brood parasites. They do not make nests of their own. They lay their eggs in the nests of other species – such as Yellow Warblers, Red-eyed Vireos, Eastern Phoebes, and more than 200 other host species, including some whose populations are in serious decline. The eggs of a Brown-headed Cowbird are incubated by the host species and the young are fed along with the young of the host species. In most cases, the Brown-headed Cowbirds are larger and fed more often, so the young of the host species may fail to survive.

Once they leave the nest, Brown-headed Cowbird juveniles continue to be fed by the host species, apparently until they are old enough to become independent and feed on their own.

So my question is: How does a Brown-headed Cowbird know it’s a cowbird? If it’s hatched, fed and raised by Red-eyed Vireos, why doesn’t it grow up to behave like a Red-eyed Vireo? When and how does it discover it’s a Brown-headed Cowbird?

In late summer and early fall, Brown-headed Cowbirds begin to gather in large flocks, so by that time, the young have somehow figured out where they belong. It’s sort of the ugly duckling story in real life, with a few unpleasant twists.

I’ve so far failed to find an answer to the question of how this actually works, but in the process of looking, have been somewhat surprised to find accounts of Brown-headed Cowbirds’ behavior and natural history much more interesting and more complex than I had expected – and ended up spending far more time on it than I meant to, and feeling considerably less antagonistic toward them than when I started.

While parasitism by Brown-headed Cowbirds is generally condemned as sneaky and especially harmful to some declining songbird species, I think it’s worth remembering that habitat loss, fragmentation and degradation are the fundamental problems – and we’re the ones who created that situation and who continue to make it worse. We’re the ones who created the kind of habitat in which Brown-headed Cowbirds thrive and many other songbird species suffer.

I still don’t like having Brown-headed Cowbirds around, but I’m not sure it’s fair to blame them.

A Yellow-throated Vireo – Seldom Heard This Year

Wednesday, May 28th, 2008

Last week for several days, a Yellow-throated Vireo sang every day all around the edges of our woods and in the oaks and pecan trees close to the house. I was happy to hear its burry, musical series of phrases because I’d just about given up hope of having one return this spring. Usually, it’s one of the earlier migrants to return, and it’s common around the edges of our woods throughout the summer, and fairly easy to locate and see. But not this year.

Rather uncharacteristically, this one stayed high in the tops of trees, where it was very difficult to see. Once I got a brief glimpse as it flew from the top of a pine to a sweet gum. The second time, I heard it singing in the topmost branches of a large pecan tree, and saw a bright yellow spot shining out from the dense green leaves. Before I could lift the binoculars, it had ducked back into the leaves, so I never got a really good look at its familiar bright yellow throat and breast, and yellow “spectacles” around its eyes. Still, the song was welcome, and knowing it was here, even if I couldn’t see it, made the woods feel more nearly complete for a while. But now it seems to have traveled on, and I haven’t heard its song since May 21.

While its relative, the Red-eyed Vireo, sings in a cool, smooth voice of the deep woods, vines, and shady places, a Yellow-throated Vireo sings a somewhat earthier, rough-edged song, reflecting the forest-edge habitat it prefers, where weeds, grasses, shrubs and small trees meet the denser woods. Though it’s associated with this kind of edge habitat, a Yellow-throated Vireo apparently needs an extensive stand of deeper forest, too. Studies have shown that it requires large areas of contiguous forest, as well as the edge habitat, in order to be successful in breeding.

Summer’s Song

Sunday, May 25th, 2008

On this Memorial Day weekend, traditionally marking the beginning of summer, an Eastern Wood-pewee made it official. Its lazy, seductive whee-oo, pee-a-wee – whee-oo arrived this afternoon in a back-yard scene of warm sun, pleasant breezes, blue sky with white clouds, and green trees all around the edge of the woods, fresh from recent rains. He stayed for several minutes, singing and hunting from the low branches of pines at the edge of the woods, just a little gray bird, but a song that’s so much a part of summer in our woodlands that they wouldn’t be the same without it.

The other sounds were more subdued, like background music. An Acadian Flycatcher sang tse-wheet from down along the creek, a pair of Summer Tanagers called pik-a-tuk softly as they moved through the leaves of the oaks, a Red-eyed Vireo chanted fast and nonstop way down in the woods, a Great Crested Flycatcher called its deep, hoarse whreep, a Pine Warbler sang a loose, warbling trill, and a Chipping Sparrow gave a long, dry, monotone trill from a shrub in the front yard. Chimney Swifts twittered overhead. One female Ruby-throated Hummingbird hummed between the feeder and a perch on a pine branch. A green anole ran along the rail of the deck, stopping to blow up its pink throat several times. Carpenter bees, tiger swallowtails and paper wasps flew in and out of the sun. Two or three juvenile Bluebirds begged for food from the parents in trees around the back yard, and juvenile Cardinals, Titmice, Carolina Wrens and Downy Woodpeckers also begged insistently.

It was a perfect afternoon to be lazy, to sit on the deck in the shade of the oaks with a book, and drift off to sleep listening to the Pewee’s whee-oo.

Summer Tanager Pair

Friday, May 23rd, 2008

Although I haven’t heard the song of a Summer Tanager as often this spring as usual – and I’ve missed it – yesterday morning I saw a pair of Summer Tanagers in the leaves of a pecan tree near our driveway, and this morning saw them again in the white oaks just behind the house. Both times they were calling to each other, with their calls overlapping, and the all-red male seemed to be following the female through the trees. I got an especially good look at the female as she paused among the leaves of an oak. Her plumage was a very attractive dusky-orange in color, with darker wings. She looked much more orange than most female Summer Tanagers I’ve seen before.

Juvenile Downy Woodpeckers – Male and Female Feeding

Monday, May 19th, 2008

On a warm, sunny, clear May morning, there were baby birds everywhere. Young Bluebirds, Cardinals, Chickadees, Titmice, and probably young Blue-gray Gnatcatchers – though they move so quickly I haven’t seen the juveniles yet, but hear them – all are shivering their wings and begging to be fed in persistent high-pitched voices.

A young male Downy Woodpecker came to a hanging block of birdseed this morning with a male parent. The juvenile looked similar to the adult, except that its crown was soft brown, with a smudge of red near the forehead. The young male sat on top of the block of seed, looked around, and waited to be fed. The adult male clung to the side of the block and pecked, and fed the youngster repeatedly for several minutes, until both flew away.

About 15 minutes later, the adult male Downy Woodpecker (I’m assuming it’s the same one) returned to the feeder, this time with a juvenile female Downy Woodpecker. The crown of her head was entirely soft brown, with no red. Unlike the young male, she clung to the side of the block of seeds and pecked at it herself and seemed to be eating. The adult male fed beside her, on the edge of the block, and occasionally offered her some food, which she accepted with a twitter of sound similar to all baby birds, then went back to pecking for herself.

Twilight Tanagers

Wednesday, May 14th, 2008

For the past month or so, one time of day when I can be sure of hearing both Summer and Scarlet Tanagers is early twilight. Not long after sunset, when light is just beginning to fade, their calls travel through the darkening woods, and sometimes through the trees around us. I can trace where they go by the calls – the soft, percussive pik-a-tuk, pik-a-tuk of the Summer Tanager, the emphatic CHIK-brrrrr, CHIK-brrrrr of the Scarlet. The Scarlet’s call is almost electric. I feel it as much as hear it.

The Summer Tanagers seem casual in their pattern of movement, as if they’re just out for an evening stroll through the woods, while the Scarlet Tanagers seem to follow a more predictable path each evening, up and down the creek, and then back toward the east, and up the hill toward our house, sometimes coming quite close. I should add that I don’t listen for them every evening and can’t say anything definitive about their movements – these are just my casual impressions.

Both Scarlet and Summer Tanagers arrived in mid April and have been singing in the woods around our house off and on all day since then, especially in the early mornings, but we seldom see them. This is unusual for the Summer Tanagers. In previous years, a pair has been a regular presence around the house – the all-red male and deep-yellow female, both with their thick bills, slightly crested heads, and somewhat furtive postures. A Summer Tanager’s song was one of the first I heard every morning, usually coming from a perch in the top of one of the trees just outside my bedroom window.

Scarlet Tanagers, on the other hand, have always been more secretive, more often heard than seen, and whenever I catch a glimpse of the male’s flamboyant scarlet and black, or the female’s olive-yellow with ash-brown wings, it seems like something special. This year, however, I’m just about as excited whenever I see a Summer Tanager, since they’ve been so much less common.

Northern Parula

Sunday, May 11th, 2008

“The parula warbler has a simple, but to my ears a very distinctive, song,” wrote Arthur C. Bent, in Life Histories of North American Wood Warblers.* “In 1900 I recorded the song in my notes as ‘pree-e-e-e-e-e-e, yip, a somewhat prolonged trill like a pine warbler’s, but fainter and more insect-like, ending abruptly in the short yip with a decided emphasis.’ I have always been able to recognize it by the explosive ending, which I never heard from any other wood warbler.”

For the past four weeks, since the middle of April, a Northern Parula – a small wood warbler that most often nests in wooded wetland areas – has been singing in the woods and even in the trees close around our house almost every day. Tiny, very quick, and constantly moving, a Parula can be difficult to see – at least for me. It usually stays well hidden, deep in dense foliage, and lately I’ve spent a lot of time staring into the green leaves of the oaks, with its distinct, beckoning song trilling right in front of me and all around me, like a tease – and I can’t see a thing. It’s like some kind of mischievous wood sprite – here, but invisible.

But once I’ve seen the female, and twice I’ve managed to spot the male.

Late on a Sunday afternoon two weeks ago – a cloudy, rainy afternoon, with watercolor-green April showers – I heard the song of a Parula in the oaks and pecans around one side of our house. After about ten minutes or so of watching and listening and following the song, I finally spotted him, perched on a small stub of a branch on a large pecan tree that was thick with dripping leaves and wet, dangling clusters of green flowers. He was preening, and at first looked all fluffed out and gray. Then he turned my way and I could see the sunny yellow throat and breast, and the smudge of dark coral in a band across the breast. He looked very small, and everything he did seemed to happen in fast-forward motion. He fanned his tail feathers, preened his breast, turned his head over a shoulder to comb the feathers there – and several times paused to lift his head up and sing. Then abruptly, he flew.

Late this afternoon, I saw him again in the same tree. Again, the weather was cloudy and wet, after a night and a day of rain. He hopped and flitted along the branches, stopping frequently to sing. I was further away this time and could barely make out the markings, but could see his diminutive shape very well, and could see as he stopped and lifted his head each time to sing the elusive but clear and crisp – pree-e-e-e-e-e-e, yip!

*Arthur C. Bent, Life Histories of North American Wood Warblers, 1953, page 144.

Disturbing News

Friday, May 9th, 2008

Today I read an Oconee Rivers Audubon email posting that noted the near absence of three or four bird species this spring at the State Botanical Garden in Athens – which has been identified by the National Audubon Society as an Important Bird Area.

Among the species of concern are Wood Thrush, which has been heard much less frequently than the last two years; Yellow-billed Cuckoo, only seen once this year; Red-headed Woodpeckers, not seen for some time now; and Swainson’s Warbler, which spent summers in the Botanical Garden through 2006, but was only seen a couple of times last year, and this year has not appeared at all. The beautiful songs of the Wood Thrush and the Swainson’s Warbler, the bold red, white and black of the Red-headed Woodpecker, and the exotic elegance of the Yellow-billed Cuckoo are all unique and integral parts of a southern woodland – and their absence is sad beyond words, especially if it continues.

Here in our neighborhood we also have not yet heard the song of a Wood Thrush or the call of a Yellow-billed Cuckoo this spring. Perhaps even more surprising here is the absence of Yellow-throated Vireos. Just last year, they were among our most regular singers all summer long – but this spring I have only heard the song of a Yellow-throated Vireo once or twice, and only in the distance, none close.

American Redstart and Bluebirds Feeding Babies

Thursday, May 8th, 2008

The bird of the day this morning was a brilliant male American Redstart that spent some time in the low branches around our front yard and even took one quick dip into the bird bath. His coal-black head and body were marked with orange wing-bars, flanks and tail-band, which he showed off by flaring his tail, and a white belly. He stayed in clear view and fairly close to me for several minutes, not at all shy, but never still for long, constantly moving.

I don’t know why, but he made me think of a cartoon bird – maybe because he was so boldly marked and colorful, and so animated, and because he gave me such a great close-up view.

It was another warm, breezy day, half-cloudy, half-sunny, with lots of bird song and activity. Both Bluebird parents made frequent trips in and out of the birdhouse. I think our pair has been a little later in nesting than others in the area.

Settling into Early Summer

Wednesday, May 7th, 2008

After being out of town for a week, I was welcomed home this morning by the deep Whreep! of a Great-crested Flycatcher hidden somewhere among the big green leaves of the white oaks beside the back deck, and the back yard looked and sounded almost like early summer. An Acadian Flycatcher called pit-SEET, pit-SEET from down near the creek. A Red-eyed Vireo sang in the woods, and a Red-shouldered Hawk called as it flew back and forth along the treeline to the east. A Parula Warbler continues to sing frequently all around the edges of the woods and even in the trees and shrubs around the house, and I’m beginning to hope the pair might stay to nest.

The weather was warm, sunny and windy. Green anoles scurried along the deck rails, stopping to pump up and down and inflate their pink throats, Tiger Swallowtails laced through the treetops, and wasps and big, droning carpenter bees buzzed around. Among the other birds singing were Black and White Warbler, Pine Warbler, Phoebe, Chipping Sparrow, Blue-gray Gnatcatcher, Scarlet Tanager, Summer Tanager (way down in the woods, not close), Titmice, and Carolina Wrens – I think a pair has built a nest somewhere in the clutter under the deck – and baby Cardinals peeped furiously, begging to be fed. Chimney Swifts chattered as they passed overhead now and then.

A female Blue Grosbeak (the first one I’ve seen this season) and a Mockingbird took turns taking full-body dips in the bird bath, and a little later a pair of House Finches came for a drink and then went on to sit on the feeder for a while. They almost always come and go together, seeming to be the most domestic of songbirds.

Our White-throated Sparrows, Yellow-rumped Warblers and Ruby-crowned Kinglets seem to have left for their summer homes while we were gone. I didn’t see or hear any sign of them today, though it’s possible a few could still be around. The greatest flush of migrants probably has passed through or arrived by now, though we haven’t yet heard or seen a Wood Thrush or a Yellow-billed Cuckoo, so I’m hoping there are still some to come. But for the most part, the rush of spring seems to be slowing into the more settled pace of early summer.