Monday, May 11, 2009

A Family Affair: American Avocet

American Avocet. Photo by David Powell

The two American Avocets stood, silent but alert, in the shallows of a New Mexico wetland. Brilliant slivers of crimson in the eastern sky heralded the onset of the day. The female had been assiduous in her companionship, and eventually the male accepted her presence. Now, the two were rarely far from one another. Like a pair of ballet dancers, the birds were the epitome of elegance with their striking feathers and graceful, upturned bills, the silhouette of their image reflected in the mirror of the glassy surface of the water.

The dance began when the female slowly and deliberately leaned forward, stretching her neck as far as possible, submerging her bill into the water. This was the cue for the male to begin his solo performance. He began to preen his feathers on the side nearest his mate, dipping his bill into the water and lifting it to his breast. With the second dip, he shook his bill splashing water on the pair. He continued, moving in an ever increasing frenzy of vigorous splashing, until he joined the still motionless female, and they became one. After, in the grande finale of their ritualized dance, the pair stood side by side with necks intertwined, and ran as one through the shallows.

Avocets prefer to nest on islands within a wetland, if possible, because it provides some protection from predators. Their nest-search, which also is part of the pair formation, includes ritualized scraping displays. The final nest site often is somewhat elevated with a clear view from which the pair can scan for predators. Sometimes, females lay eggs in the nest of another female, who then incubates the eggs. Avocet eggs have been found in the nests of other species too, such as gulls. Likewise, eggs of other species sometimes are found in avocet nests. So, an avocet parent might raise a mixed species family that could include Black-necked Stilts or even terns.

Modern day parenting is the norm, where both parents take turns incubating the average size clutch of four eggs. Early on, the male performs on the bulk of incubation. In warmer areas, with relentless sun baking the sandy shores, incubation consists of cooling, rather than warming, the eggs. Parents soak their belly feathers before sitting on the nest. Evaporative cooling prevents the eggs from getting too warm.

For a vulnerable chick, life on the edge of a wetland is precarious. Young are up and out of the nest within 24 hours. Day old chicks can already walk, swim, and dive. Older, but still flightless, chicks can dive and swim up to 21 feet underwater using their wings and feet. If the nest is on an island, chicks follow their parents and swim to the shore, where they are raised in a nursery area with shallow water and dense vegetation for cover. Often, several avocet pairs will cooperatively raise their young in a communal nursery. Here, the chicks might a brooded by different parents.

Often, female parents abandon the nursery before the young a fully independent, leaving the remainder of the care with the males. Maybe, just maybe this is part of the reason why he is reluctant to initiate courtship, knowing what his parenting duties will be, and why avocets rarely have the same mate the following season.

Sunday, May 10, 2009

What's in a Name: Wood Warblers

Yellow Warbler. Photo by David Powell
Yellow-rumped Warbler. Photo By David Powell.

Imagine sitting on the deck overlooking the Jemez River on the first beautfiul spring morning spring morning of the year. The streamside vegetation is bursting with new green verdance. As the caffeine from your coffee or tea begins to work its morning magic and the sleep induced blurriness clears from your eyes, you realize that today the world is a little different. Tiny little birds of brilliant yellow, black, green, and blue flit among the tree tops and bounce across the streamside vegetation oblivious to your presence. They’re in a hurry, these little birds, gobbling up bugs as if they’ve not eaten in a long time, hastily replenishing their fat reserves. Every so often, one of them appears to forget the business of survival, and bursts into song, often from the very top of a very exposed perch, as if he were warbling his presence to the world. Indeed, he is doing just that but, in truth, he cares little for planetary interest. His serenade is meant for only one, a certain special female.

Warblers, properly known as wood warblers, have long captivated bird watchers with their diversity, bright plumages and sprightly behavior. Most of them winter in Mexico, Central and South America, and return to our latitudes in late April and May. Down south, during the winter, they were busily eating as much as possible, mostly insects, so they could produce an entirely new set of iridescent feathers and attain prime breeding condition. They’re hungry when they arrive after their long journey, often feeding voraciously in the densest vegetation of the very tops of the tallest trees. Warbler watching is not for the faint of heart. There’s actually a name for this particular sports injury, “warbler neck”. It feels as if your binocular strap is literally going to sever your head from your body. It hurts

I clearly remember a trip to southern Arizona, to the upper reaches of the Chiricahua Mountains on a quest for rarities, one of which was the Olive Warbler. The habitat preference of this little fellow is the tip top of the tallest pines. We heard him sing almost as soon as we arrived and occasionally saw something flit way up there. My neck loudly proclaimed its discomfort as I searched through the tips of the pine forest without capturing one in my binoculars. Then, just when I was about to give up, I realized that I didn’t necessarily have to stand with bowed back and bent neck. My friend and I decided to lay down in the grass and watch from a more natural body postition. Voila Olive Warbler added to my checklist

Warbler watching is not for everyone, but some dedicated birders travel far afield to places like High Island, Texas each spring. This tiny island on the north shore of the Gulf of Mexico hosts the first trees and shrubs seen by trans-gulf migrants after flying nonstop across hundreds of miles of water, a nonstop trip of 36-45 hours across the hostile ocean. Exhausted, the tiny birds fall from the sky, resting and eating within easy sight of the average birder.

Our western warblers make and overland journey north along the spine of the continent and its watersheds. While many species migrate through, only a few stay to nest: Yellow-breasted Chat (our largest warbler), Common Yellowthroat, and Yellow, MacGillivray’s, Grace’s, and Virginia’s Warblers are the most common Jemez nesting warblers.

Insect larvae comprise the bulk of the diet of all warblers, although fruit and nectar are seasonally important for some species. Just as species occupy widely differing habitats, their feeding styles vary widely. Some are gleaners, patiently plucking insects from leaves and bark, moving slowly and reaching for the next morsel, like our Grace’s Warbler that probes pine needles, bark, and crevices in the ponderosa pine forest. Some skulk in dense vegetation, often along streams, picking insects from clusters of dead leaves on the ground or bark and vegetation just above, like MacGillivray’s Warbler. Others prefer to hang from or flutter beneath vegetation, gleaning prey from the underside of leaves, like the Wilson’s Warbler that migrates through New Mexico and breeds in our northernmost coniferous forests. This tiny, bright yellow fellow with the solid black cap is constantly on the move. In fact, “the bird that can’t stop moving” is one of the ways to help identify the species. Some warblers, like the Yellow-rumped Warbler, employ a sallying technique, flying quickly out from a perch to snatch an aerial insect, also called flycatching.

While warblers occupy themselves with survival, we humans wrestle with cataloguing and naming all things on our shared plant. It can be the cause of strife and dissension, with a heavy dose of ego. In the world of ornithologists, the honor of naming a bird is bestowed on the person that discovers the new species, but naming a bird after oneself is frowned upon by the scientific community. Changing a name, once bestowed, can be construed as scientific jealousy and cause for scorn.

Some species have names that reflect something about their biology, such as the Field Sparrow, often found in weedy fields, or Swamp Sparrow. Others are named after their song or call, such as the chickadee with its ‘chick-a-dee-dee-dee’ call. Some choose to name the newly discovered species after another individual, generally another revered scientist. However, controversy sometimes rears its ugly head when egos are overly invested in a name.

Such was the case with our beautiful MacGillivray’s Warbler. It was discovered by eminent ornithologist, John Kirk Townsend, who named it after his close friend, Dr. W. T. Tolmie, Esq., a surgeon, noted ornithologist, and entrepreneur with the Hudson Bay Company. The new species was called Tolmie’s Warbler. Later, however, in Birds of North America, John James Audubon renamed the species MacGillivray’s Warbler in honor of his close friendship with Dr. W. MacGillivray, a Scottish ornithologist and professor of natural history who had helped Audubon edit his book. Audubon’s disregard for Townsend’s prior name and MacGillivray’s lack of North American field experience have caused resentment among some western birders, who still prefer reinstating the original name. Fortunately, the warbler shares none of our concern about his name. He’s too busy just doing what comes naturally.