Modeling the ecological trap hypothesis: A habitat and demographic analysis for migrant songbirds

Most species occupy both high- and low-quality habitats throughout their ra nges. As habitats become modified through anthropogenic change, low-quality habitat may become a more dominant component of the landscape for some spe cies. To conserve species, information on how to assess habitat quality and guidelines for maintaining or eliminating low-quality habitats are needed. We developed a source-sink population model that depicted the annual cycle of a generalized migratory Songbird to address these questions. We determi ned how demographic factors, landscape composition (the percentage of high- and low-quality habitat), and habitat selection interacted to promote popul ation persistence or extirpation. Demographic parameters, including adult a nd juvenile survival, nesting success (probability of a nest successfully f ledging one or more young), number of nesting attempts, and number of young fledged per nest, interacted to affect population growth. In general, popu lation growth was more sensitive to adult and juvenile survival than to fec undity. Nevertheless, within typically observed survival values, nest succe ss was important in determining whether the population increased, decreased , or was stable. Moreover, the number of nest attempts by females and the n umber of young fledged per nesting attempt influenced population stability. This highlights the need to obtain more complete demographic data on speci es than simple nest success to assess habitat quality. When individuals sel ected high- and low-quality habitats in proportion to habitat availability, populations persisted as long as low-quality habitat did not make up > 40% of the landscapes. However, when individuals preferred low-quality habitat s over high-quality habitats, populations were extirpated in landscapes wit h > 30% low-quality habitat because low-quality habitat functioned as an ec ological trap, displacing individuals from high-quality to low-quality habi tat. For long-term conservation; we emphasize the need for basic informatio n on habitat selection and life-history characteristics of species througho ut their range.