creative nesting strategies and social systems

Eleven species of shorebirds may nest in Southeast, according to Armstrong’s Guide to the Birds of Alaska. At least six of those are known to nest in the Juneau area. One additional species, the least sandpiper, was formerly relatively common near the airport dike trail and on the glacier forelands, but increased dog and human activity, plus habitat changes in those areas, have greatly reduced and perhaps eliminated this species as a local nester.

The term ‘shorebird’ reflects the fact that most people see them in winter and on migration, when these birds typically forage on shorelines. The Mendenhall wetland, for example, is recognized as a globally important stopover site for lots of migrating shorebirds. In fact, however, many shorebirds do not nest near shores. Instead, they commonly nest on tundra, in alpine zones, in forest, grassland, and muskegs.

I encounter spotted sandpipers most frequently, because they nest near rivers, lakes, or saltwater, on beaches and gravel bars. I see nesting semipalmated plovers in the tern colony near the glacier and also along marine shores. Killdeer try to nest in gravel pits, on flat rooftops, and at the edges of parking lots where the eggs are at risk of getting crushed. When I venture into muskegs in the nesting season, greater yellowlegs are hard to ignore, because they usually shriek and swoop and dive-bomb any intruder. I almost never see nesting Wilson’s snipe, but I hear them doing their aerial display high over their wet grassy or sedgy meadows—it’s called ‘winnowing’, from the sound made by air whooshing through their spread tail feathers. And nesting solitary sandpipers in their wooded wetlands I virtually never see; apparently few other folks see them either, to judge from the little research that’s been done on them.

Shorebirds are generally ground-nesters, but the solitary sandpiper is a notable exception. This species has the peculiar habit of nesting in the abandoned nests of songbirds such as robins, jays, and blackbirds. It is the only shorebird in North America to do so, and one of only two species in the world with this habit. After claiming a nest, the pair may make slight renovations to the basic structure. I wonder if they ever take over a newly built nest, driving away the owners! A pair of solitary sandpipers was known to nest this year in a flooded, shrubby area near the glacier, although we never found the nest itself.

Solitary sandpiper. Photo by Bob Armstrong

After I contemplated this strange habit for while, I realized that using an old songbird nest might be a great strategy. Predators (and bird-watchers) often find songbird nests by watching adult birds go to and fro, carrying nesting material or feeding chicks. Solitary sandpipers, however, don’t carry nesting material or feed their chicks. The chicks are precocial—hatched covered with fluffy down, eyes wide open, and able to run or swim almost immediately. So many of the usual cues for nest-finding are absent. But that leaves the question of how this nifty trick got started…

In general, our locally nesting shorebirds lay three or four eggs, but patterns of parental care vary considerably. Most of these species are socially monogamous (one female paired with one male, although copulation is not necessarily restricted to the mated pair), but some engage in degrees of extra-curricular activity, by mating with the neighbors as well. Both males and females can incubate eggs, apparently, except in Wilson’s snipe; in this species only the female sits on the eggs, and she does so for three to four weeks. During that time, the males are busily seeking extra-pair copulations. Male snipe make up for their lack of egg-tending, so to speak, by caring for some of the chicks (of which he may or may not be the father, because all his neighbors were as busy as he was). Snipe are unusual among shorebirds in that the parents actively feed their chicks for several weeks, and don’t just lead their chicks to food as the other species do.

Spotted sandpipers are exceptional to the usual arrangement of social monogamy, because they are often polyandrous: one female pairs with two to four males, either simultaneously or sequentially. Females hold large territories that include the smaller territories of her males. Males do most of the parental care, including incubation, but females may help at her first nest (until she gets another male) and at the nest of her last male of the season. Females even beat up their mates, sometimes, if the males are neglecting their incubation duties. Competition is fierce among females for males, and among females if certain females are perceived as especially desirable.