Its wings and wing muscles are reduced; it prefers to freeze in place when pursued. Energetic foraging behavior includes a fly-snapping sprint through "Neoscatella sexnotata" brine fly swarms. With necks outstretched, and bills close to the ground, the ducks run along a mudflat and as clouds of flies rise up in front, snap them up by rapidly opening and closing their bills. The ducks also will dabble and filter feed along lake shallows, shore, and in upland vegetation for macroinvertebrates, algae, leaves, and seeds. During the day, and especially in the breeding season, they prefer to hide among the grass and shrub vegetation, helping them to avoid avian predators such as frigatebirds. They prefer to venture out in the open and feed on the lake from dusk til dawn, although there seems to be marked variation from year to year according to the availability of food items. Pair formation begins in fall, and nest building begins in spring. The female builds a well-concealed nest on the ground below dense vegetation, especially "Eragrostis variabilis" bunchgrass. The nest is a shallow bowl lined with dead grass and down feathers. Egg-laying typically occurs from April to August. Average clutch size on Laysan Island is approximately four bird egg/eggs. The newly established population on Midway lays larger clutches, presumably because of better availability of food. Ducklings are precocious and feed on their own day two after hatching, but are guarded, brooded, and led to foraging sites by the hen for approximately 40 to 60 days. The decline of the Laysan duck began between AD 400 and 1000, with the colonization of the Hawaiian Islands by Polynesians and associated non-native mammalian predators. By 1860, the ducks disappeared from all but Laysan Island (the duck's namesake), most likely due to predation by introduced rats. Like many isolated island species, the Laysan duck evolved in an environment lacking mammalian predators, and is ill-suited to defend itself against non-native ground hunters, such as humans, rats, pigs, and small Asian mongooses. For example, Laysan ducks are more likely to freeze their movement rather than flush or fly when startled— a strategy well suited for cryptic defense against Hawaii's native flying predators, but ineffective against ground predators. The Laysan duck can still fly, but not very well and not for long distances; it does not disperse between islands.