Reply to Urquhart: Conservation of migratory double breeders

Urquhart (1) raises additional potential conservation implications of our discovery of migratory double breeding in several Neotropical migrants (2) and suggests that source sink thinking is not appropriate for this situation. We fully agree. Consider the yellow-billed cuckoos as a hypothetical example. What we need to know is whether either breeding population is self-sustaining. Suppose the population growth rate, λ, is < 1 both in the early-summer breeding range and in the late-summer breeding range, but > 1 for individuals that breed in both areas. In this case, conservation of cuckoos will be inextricably linked between these areas. A …