Does forest fragmentation and loss generate sources, sinks, and ecological traps in migratory songbirds?

摘要: Forest fragmentation and habitat loss on the breeding grounds of migratory songbirds have long been hypothesized to create source–sink dynamics. fragments increased populations many nest predators that are subsidized by food in surrounding landscape themselves released from top predators. Migratory also susceptible brood parasitism brown-headed cowbird ( Molothrus ater ). As a result reduced nesting success, reproductive output may be driven below threshold. Source–sink dynamics occur within forest tracts, among patches landscape, over entire regions which sink small tracts mostly agricultural rescued distant source forested regions. In absence ongoing loss, will only generate continuing population declines if birds lack behavioral mechanisms enable them concentrate avoid sinks. If is attractive, then it can become an ecological trap. There growing evidence use decision rules based success might traps created high rates predation. Most birds, however, do not areas with heavy parasitism. are, number limitations fragmentation–source–sink paradigm. First, there critical need for improved data survival adult young birds. Second, we know very little about spatial scale dispersal most species. Third, fragmentation-associated reductions appear much weaker some regions, especially western North America. And fourth, far clear large always act as populations. Nevertheless, conservation strategy maintains or restores seems likely maximize ratio lead sustainable