Ecology 6th Edition by Charles Krebs

Exercise 6

Kirtland's warbler is an endangered species that breeds in northern Michigan jack pine forests. From the 1950s to the 1970s the population of this species declined, and it numbered about 200 individuals in 1971. It was stable in numbers from 1971 to 1986. The most important factor in the population decline seemed to be increasing parasitism of nests by brown-headed cowbirds. Cowbirds were removed from the breeding area of Kirtland's warbler starting in 1971, but no change occurred in warbler numbers by 1986, and speculation began that it was being limited on its wintering grounds in the Bahamas. The alternative hypothesis was that habitat was becoming unsuitable for these birds. Extensive habitat management was begun in 1987 and two large wildfires rejuvenated the jack pine stands in which it breeds. The warbler increased in numbers fourfold in the 1990s. What management plans would you now recommend for this endangered species? Probst et al. (2003) provide recent evidence on this endangered bird.