Showing posts with label Shorebirds. Show all posts
Showing posts with label Shorebirds. Show all posts

Thursday, September 9, 2010

The Noisemaker: Killdeer

Famous for its broken wing display, the Killdeer thrives in a human-altered environment. Photo by Doug Brown.

"Killdeer! Killdeer! Dee, deet, dit!” The piteous, shrill wailing call that emanated from the depths of the ink-black sky told the casual listener that somewhere overhead a bird was in the throes of agitation. This might seem to be unusual since most birds do not vocalize after dark lest a nocturnal predator, such as a Great Horned Owl, be alerted to their presence. Not so with the little shorebird currently called a Killdeer for the distress call it uses during the peak of terror, or possibly excitement. The small, plover-like bird is known for its vocal nature and was, in times long ago, called Chattering Plover (1731) and Noisy Plover (1785).

Unlike its plover cousins that inhabit shorelines where they prey on small aquatic prey, you can see a Killdeer without going to the beach. They are quite common in New Mexico throughout the year, frequenting sandbars, mudflats, grazed fields, lawns, golf courses, athletic fields, and parking lots. It is one of the most successful of all shorebirds precisely because of its fondness for human modified habitats and its willingness to nest close to people. For these same reasons; however, they are vulnerable to pesticide poisoning, oil pollution, lawn mowers, and collisions with cars.

Usually they are found near water of some sort, although their idea of adequate water might just be a lawn sprinkler. They thrive in short vegetation averaging about one inch in height. Thus golf courses with abundant sand traps are just about ideal from the bird’s point of view, as they provide three habitat essentials: water, a variety of grasses and grass heights for hunting insects, and sand for nesting.

This small white and tan bird with the black neck band and overly long legs can often be seen in dry, flat landscapes, running across the ground in short spurts, stopping suddenly every once in a while to see if they’ve startled up any delectable insect or earthworm treats. Like many raptors, Killdeer have learned to follows farmers' plows in hopes of retrieving any unearthed worms or insect larvae. Opportunistic, they also have been observed hunting frogs and eating dead minnows.

Killdeer are famous for their broken-wing display where they try to lure predators away from their nest by feigning injury. The bird runs a little, clearly dragging one wing, leading the observer to either view it as an easy meal or as a bird in need of rescuing. As the observer draws closer the bird stays put until the last moment when it runs again, always remaining just out of reach until the bird feels it has drawn the potential predator far enough away from its vulnerable eggs or young.

The broken-wing act does not work against intrusions from cows or cattle, animals that have little interest in a small brown bird. For this type of threat, the Killdeer uses a very different display, fluffing itself up and displaying its tail over its head. Then, it runs straight toward cow/horse animal in an attempt to divert the animal.

Although numbers of Killdeer are likely as high today as at any time in their history due to their fondness for the habitats we create, at one time the population was in serious decline due to hunting pressure. In the mid-1800s, Killdeer were common in markets year-round although, according to Audubon, their flesh was “indifferent” except for fat young birds in autumn. In the South, they were captured with a hook and line baited with a worm. Sometimes, they simply were shot on sight because their noisy warning call alerted other game species of the hunter’s approach.

In the early 1900s, laws were passed by some states to protect Killdeer, but widespread protection finally occurred because of the very low numbers, the fact that the meat was not particularly tasty, and because humans recognized the bird’s beneficial habit of devouring insects. Today, Killdeer are among the most successful of shorebirds, particularly in our human modified habits. We’ve come a long way, from predation to appreciation.

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.