Release of Captive-Reared or Translocated Endangered Birds: What Do We Need to Know?

Abstract

Attempts to evaluate the success of endangered-species reintroduction programs are frustrated by a lack of reliable information on releases of either endangered or nonendangered species. Although many programs have attempted to establish or augment wild populations with captive-reared or wild-caught birds (Williams 1977), there are few published accounts that allow quantitative statements on the success of releases and the role played by animals subjected to different rearing and release protocols (Berger 1978, Kear and Berger 1980). This makes it difficult to assess accurately the status of these species, or to evaluate the influence of various management actions. The U.S. Fish and Wildlife Service (hereafter USFWS) lists 220 taxa of birds as threatened or endangered (USFWS 1986). Recovery plans exist for 45 of them. Captive rearing is cited frequently in recovery plans as a requirement to ensure the recovery of these species. Captive rearing of species with release to the wild is an important management technique used in attempts to save species from extinction (Mar-tin 1975, Temple 1978, Carpenter and Derrickson 1981, Carpenter 1983). Reintroduction generally is initiated only after more conservative techniques (e.g. habitat protection, law enforcement, and public education) have been unsuccessful in restoring population levels. Captive propagation is viewed by many as the last possible action appropriate for only a few select species (Conway 1978, Scott et al. 1986a, Temple 1986). Potential benefits of reintroduction programs include (1) increasing the number of animals in a small population , (2) increasing genetic diversity in a small population, (3) reducing inbreeding depression in small populations, and (4) establishing new populations. There are many examples of vigorous new populations of nonendangered bird species being established outside their historical ranges, and many undocumented failures (Long 1981). Earlier workers (Warland 1975, Fyfe 1978) were unable to document an endangered or threatened bird species that had been restored to a self-sustaining wild population as the result of releasing captive-reared birds. Even the claims of success for the Hawaiian Goose (Nesochen ' Idaho Cooperative Fish and Wildlife Research Unit,