Whooping crane recruitment enhanced by egg removal

Abstract

To facilitate recovery through captive breeding and foster-parenting programs of the endangered whooping crane, one of two eggs was removed from 62% of nests in Wood Buffalo National Park during 1967–1996. Egg removals were justified because cranes usually rear a single chick; the other dies to siblicide or predation. Concerns exist that the wild population might have recovered even faster if nests had not been disturbed. Here we show, contrary to expectation, that removing one of two eggs from a whooping crane nest actually increases the probability of nest success, and this effect is highly correlated with the dynamics of predators in the nesting area. These results beg the question: why do whooping cranes lay two eggs? We attribute two-egg clutches to occasional “good years” in which both chicks survive, compensating for higher mortality in two-egg broods. Egg removal has benefited conservation allowing establishment of several captive flocks, supporting reintroduction of two new populations, and reducing the variance in reproductive success of the wild flock thereby minimizing extinction risk.