Merlin

Black-necked Stilt Life History

Habitat

Habitat Marshes

Black-necked Stilts inhabit shallow wetlands with limited vegetation, including salt ponds and pans, flooded areas along rivers, shallow lagoons, saltmarshes, mangrove swamps, and mudflats. Sewage ponds, evaporation ponds, rice fields and other flooded agricultural fields, and other human-created wetlands also attract stilts—and in some areas stilts actually favor these habitats over available natural habitats. Although stilts tolerate more vegetation in their nesting areas than avocets do, they nest and forage in areas with large openings of shallow water, such as in saltmarshes. Migrating and wintering stilts select habitats similar to those used in the breeding season. In Hawaii, the endemic subspecies of Black-necked Stilt regularly forages in the freshwater fish impoundments created by ancient inhabitants of the islands.

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Food

Food Aquatic invertebrates

When they are not resting or preening, Black-necked Stilts spend much of the day wading in shallow waters to capture aquatic invertebrates, small crustaceans, amphibians, snails, and tiny fish. They prey on larval mosquitoes, soldier flies, brine flies, caddisflies, dragonflies, mayflies, crickets, grasshoppers, many kinds of beetles (including weevils), water-boatmen, crayfish, brine shrimp, tadpoles, and very small frogs and fish. These are captured with a quick peck, sometimes with the head partly (and quickly) submerged. Sometimes, they swing the bill side to side in the water, much as avocets do, to skim invertebrates from the surface or just below the surface. To capture small fish, they sometimes chase them into the shallows, where the fish become trapped. Seeds and vegetation form a tiny part of the diet.

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Nesting

Nest Placement

Nest Ground

Black-necked Stilts nest on the ground. They tend to build on surfaces above water, such as small islands, clumps of vegetation, or even, occasionally, floating mats of algae. Both female and male choose the site; they look for places with soft sand or other substrate that can be scraped away to form the nesting depression. The nests are often set among vegetation stubble adjacent to water or on dikes, islands, or high spots with sparse vegetation such as glasswort and saltgrass.

Nest Description

Males and females share the work of nest construction. While one observes, the other scrapes into the dirt with breast and feet to form a depression about 2 inches deep. As they dig, they add small bits of lining back into the nest. Most lining is added to the nest during incubation and consists of whatever material is closest to the nest, including grasses, shells, mud chips, pebbles, and bones. Some nests are left unlined.

Nesting Facts
Clutch Size:2-5 eggs
Number of Broods:1 brood
Egg Length:1.5-2.0 in (3.7-5.1 cm)
Egg Width:1.1-1.3 in (2.9-3.2 cm)
Incubation Period:24-29 days
Egg Description:

Tawny olive to light drab with dark brown speckling.​

Condition at Hatching:

Covered with down and able to run awkwardly within about 2 hours of hatching.

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Behavior

Behavior Probing

Black-necked Stilts are especially animated during the breeding season, when females select males for mating. Just before mating, the female stretches out the neck and preens; the male faces her and does the same. Both dip the bill in the water and preen the breast, and this action becomes increasingly frenzied, with much splashing just prior to copulation. Afterward, the pair crosses their bills and runs together for a few steps. Both sexes participate in incubation and chick-rearing, though males appear to accompany older chicks more often than females. The pair bond is maintained through nesting and chick rearing, but if a nest fails, stilts sometimes begin again with a different mate. Stilts nest in loose colonies and are considered semicolonial, defending individual territories (and guarding mates) but joining with other nesting stilts to drive out threats. Predators, and humans, that happen near nesting stilts soon learn that they are not welcome: any birds that are not incubating often fly around or even form a ring around the predator, calling loudly as they leap up and down, flapping their wings (called a “Popcorn Display” by researchers). They also perform distraction displays, such as pretending to be incubating, then flying off to another site and repeating the deception. Sometimes, stilts will strike humans from behind with their legs if the humans approach the nest too closely. Adult stilts are highly territorial. Males often challenge one another early in the nesting season, stretching out into upright stances, or racing at each other with necks contracted and tails raised. Intense conflicts sometimes involve aerial combat in which males strike each other with bills and legs. Territoriality extends to driving out young birds as well: adults sometimes attack stilt chicks that are not their own and even avocet chicks. Small chicks can dive and swim underwater to avoid hostile adults and predators. When not breeding, Black-necked Stilts are still fairly territorial but often will roost and forage in close proximity, if never in the tight flocks formed by avocets. When resting, stilts sometimes draw up one leg, resting on the other, or sit on the ground, resting on the lower, longer part of the leg (called the tarsometatarsus).

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Conservation

Conservation Low Concern

Black-necked Stilt populations have been stable between 1966 and 2015 in continental North America, according to the North American Breeding Bird Survey. Partners in Flight estimates the global breeding population at 900,000 birds, with a Continental Concern Score of 8 out of 20, indicating it is a species of low conservation concern. There is some evidence of range expansion to the north, possibly attributable to climate change. The Hawaiian subspecies of Black-necked Stilt (knudseni), called the Ae'o in the Hawaiian language, is listed as federally endangered. Ae'o numbers have risen slowly in the past 30 years, but there are still fewer than 2,000 individual breeding birds. Because stilts are wetland birds, they are vulnerable to wetland destruction, degradation, and especially pollution, including pesticides, heavy metals, and other elements such as selenium. Stilts are sometimes monitored as indicators of contaminated irrigation water in the environment at large. In Hawaii and elsewhere, invasive aquatic plants deprive stilts of open water and mudflats. In the nineteenth century, stilts were hunted throughout their range.

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Credits

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Robinson, Julie A., J. Michael Reed, Joseph P. Skorupa and Lewis W. Oring. (1999). Black-necked Stilt (Himantopus mexicanus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxtent Wildlife Research Center (2014b). Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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