Abstract
Many species of mature forest-nesting birds (“forest birds”) undergo a pronounced shift in habitat use during the post-fledging period and move from their forest nesting sites into areas of early-successional vegetation. Mortality is high during this period, thus understanding the resource requirements of post-fledging birds has implications for conservation. Efforts to identify predictors of abundance of forest birds in patches of early-successional habitats have so far been equivocal, yet these previous studies have primarily focused on contiguously forested landscapes and the potential for landscape-scale influences in more fragmented and modified landscapes is largely unknown. Landscape composition can have a strong influence on the abundance and productivity of forest birds during the nesting period, and could therefore affect the number of forest birds in the landscape available to colonize early-successional habitats during the post-fledging period. Therefore, the inclusion of landscape characteristics should increase the explanatory power of models of forest bird abundance in early-successional habitat patches during the post-fledging period. We examined forest bird abundance and body condition in relation to landscape and habitat characteristics of 15 early-successional sites during the post-fledging season in Massachusetts. The abundance of forest birds was influenced by within-patch habitat characteristics, however the explanatory power of these models was significantly increased by the inclusion of landscape fragmentation and the abundance of forest birds in adjacent forest during the nesting period for some species and age groups. Our findings show that including factors beyond the patch scale can explain additional variation in the abundance of forest birds in early-successional habitats during the post-fledging period. We conclude that landscape composition should be considered when siting early-successional habitat to maximize its benefit to forest birds during the post-fledging period, and should also be included in future investigations of post-fledging habitat use by forest birds.
Highlights
To address long-term declines in populations of Neotropical migratory bird species, conservationists need to understand the resource requirements and factors affecting survival of these species throughout their lifecycle
While past research has greatly improved our understanding of post-fledging ecology [3,4,9,10,12,13], these findings vary considerably relative to the factors they cite as influencing the abundance of forest birds during the post-fledging period, some highlighting the importance of fruit abundance and others emphasizing dense vegetation providing protection for predators
We examined the influence of local and landscape-level factors on the captures of post-fledging forest birds using generalized linear mixed models (GLMM) specified with a Poisson distribution with a log-link function and fitted with Laplace estimation
Summary
Previous studies have shown that mature forest-nesting birds (‘‘forest birds’’), a group including species of particular conservation concern [7], undergo a pronounced change in habitat use during the post-fledging season, and move from their forested nesting sites into areas of early-successional vegetation. This habitat shift has been attributed to birds seeking out areas with increased understory vegetation and food abundance, resources presumed to enhance survival [3,8,9,10,11]. There is reason to expect that the inclusion of landscape factors into models of forest bird abundance during the post-fledging period will increase our ability to explain variation in forest bird abundance in early-successional habitats during the post-fledging period
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