Social and environmental constraints on breeding by New Zealand snipe Coenocorypha aucklandica.

New Zealand Snipe Coenocorypha aucklandica on the Snares Islands occurred at high densities and many males were unable to obtain territories. Territory ownership was a prerequisite for obtaining a mate, and most matings were monogamous. Territorial males guarded their mates, but did not exclude subordinate birds from territories. Females were courtship-fed by their mates for three weeks before laying; laying occurred earlier in years when food was more abundant, as females reached threshold laying weights sooner. Incubation was shared and took 22 days. Females that mated with males that were already paired incubated unaided; an egg in one such nest hatched after about 38 days. The earliest hatch dates coincided with the annual peak in food availability. Broods were split at hatching, each parent caring for one chick independently. Chicks were fed by their parents for at least 41 days. Food availability during the period that chicks were reared was significantly higher than during the pre-chick period. During chick-rearing, territories were usurped by subordinate males, which courted available females and sometimes bred. Failed pairs frequently renested, but no pairs were double-brooded. Some breeders of both sexes that lost their dependent chick bred a second time with a new mate while their first mate continued rearing the surviving chick. Territory and mate fidelity of breeding adults were very high, and were not affected by breeding success in the previous year. Nonbreeding adults obtained a permanent territory and mate only if a territorial bird died. Prior residency was an important factor in acquiring a territory both within and between seasons. Mortality of adults during the nonbreeding season was density-dependent. However, exceptionally high mortality occurred in the winter following the 1982-83 El Nino event. Widespread reproductive failure and late breeding by snipe in 1982-83, and high mortality during the 1983 winter were probably caused by climate-induced reduction in their invertebrate food supply. Compared with other snipe, New Zealand Snipe had much higher parental investment by both sexes, and much lower per pair potential reproductive output. The highly K-selected breeding system of New Zealand Snipe is considered an evolutionary response to high intraspecific competition for food during the breeding season. The low reproductive rate, and density-dependent mortality during the nonbreeding season indicate that New Zealand Snipe were limited by food throughout the year. These findings support Ricklefs' (1980) contention that bird populations in stable environments are limited by intraspecific regulatory processes.