Contrary to what it’s called, the “fall” migration of shorebirds has been underway since early July, and is in full swing, peaking in August. Vermont is home to only a few breeding shorebirds (Killdeer, Spotted Sandpiper, Upland Sandpiper, Wilson’s Snipe, American Woodcock). Most of the shorebirds we see this time of year are those migrating south after nesting in the Arctic.
Shorebirds move south relatively early compared to many migratory birds, in part, because the breeding season in the Arctic is quite short. In addition, those birds whose first nesting attempt failed tend to migrate soon afterwards rather than attempt a second nesting, due, once again, to the brief Arctic summer. Also, in several species one member of a pair often leaves before the young are full grown, sometimes even before the eggs hatch, leaving the remaining adult to raise the young.
The young of most shorebirds migrate later than the adults. There can be as much as a month between the peak passage of adults and that of juvenile birds. (Photo: Greater Yellowlegs)
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Ninety-eight percent of a Killdeer’s diet consists of animal matter. Beetles, insect larvae, earthworms, grasshoppers and crayfish make up the majority of what a Killdeer eats. In the summer, adult beetles (see photo) and beetle larvae make up almost half of what they consume.
Much of the time we observe Killdeer they are running, stopping, waiting and then running again. This is typical feeding behavior. Another method of obtaining food consists of patting the ground or the bottom of a pond in shallow water with one quivering foot. Killdeer also engage in probing into mud and chasing prey, and they have been known to follow tractors in search of earthworms.
Food normally passes through a Killdeer’s digestive tract in about two hours, but the spore-bearing structures of some ferns that it eats take five to sixty hours. All birds have gizzards, where food is ground up. Some birds swallow grit to aid in the grinding process, and the Killdeer is one of them. It has been proposed that the sporocarps take longer to pass through a Killdeer because they are retained in the gizzard where they function as grit.
Killdeer that breed in the southern half of the U.S. are year round residents, and do not migrate, but in the northern half of the U.S. killdeer are migratory. Their wintering range extends across the southern tier of states, through Mexico and the Caribbean and along the coastal regions of western South America (Columbia, Venezuela, Ecuador and Peru). Killdeer that breed in the Northeast overwinter in Gulf and southern states that border the Atlantic Ocean.
The first returning killdeer have been sighted in Vermont. While the spring migration of killdeer is early, it is also prolonged, peaking in late March or early April in New England. Killdeer migrate during the day as well as at night, in flocks of 6-30 birds. When they stop to rest and/or forage, the birds typically do not go within 13 to 20 feet of each other, and are met with aggression from other flock members if they do. Once on their breeding grounds, killdeer are even less tolerant of each other. The courtship behavior in one pair often elicits aggressive behavior from neighboring pairs.
Now is the time to keep ears and eyes open for this inland-nesting shorebird. Corn fields, lawns and parking lots are a good place to start. For a perfect example of onomatopoeia, listen to Lang Elliott’s killdeer recording: http://www.langelliott.com/mary-holland/killdeer/ (Sound recording © Lang Elliott – langelliott.com)
This is the time of year when it pays to watch where you walk – there are a number of ground nesting birds, some of which, including killdeer, may choose your lawn or even your garden to build their simple “scrape” nest. Typically killdeer nest on the shoulders of roads, gravel roof tops, fields and gravel parking lots. The nest is very primitive, and there’s actually very little to it — killdeer scrape a slight depression in the ground, to which they often add bits of material, including white objects such as shells and bones. Their pigmented eggs are extremely well camouflaged. The young precocial killdeer chicks are on their feet and feeding themselves as soon as their down feathers dry. (Photo by Sadie Richards)