Print PageWe aim at understanding the role that small, scattered patches of vegetation within urban spaces have in sustaining bird migration. In the Northeast, the main migratory flyway overlaps the most urbanized region of North America and forms a potential physical barrier for migrants. It has been shown that many migrants rely on stop-over sites to replenish spent energy. Therefore, the presence of suitable habitats within a matrix of urban land can be critical for the survival of many migratory birds that migrate through extensive urban areas. Therefore, the study is focused on a 520 square meter wooded plot in downtown Newark (Rutgers Newark Campus) to determine if the necessary conditions are provided for birds to replenish depleted fat stores during stopover. In particular we ask whether and how long birds stay and whether they gain or lose body mass during their retention in the urban habitat. During fall of 2010 630 passerines were captured in mist-nets and banded to obtain measurements of body mass and overall body conditions. Nets were deployed and controlled almost daily from September to mid November and recaptured birds were re-weighed and their fat deposits assessed.
Results/Conclusions
Total recaptures for four abundant species (Ovenbird, Hermit Thrush, Swamp Sparrow and White-throated Sparrow) were 69 individuals which resulted in an average recapture rate of 26% (range: 10-47%). The average stay for the four species on the site was 2-8 days. This high recapture rate and the calculated residence times are an indication that the urban habitat patch indeed acted as stopover site. Analysis of mass gain throughout duration of stopover indicated contrasting stopover strategies amongst the four species. Short range migrants such as Hermit Thrush and Swamp Sparrow showed that most gain in body weight occurs during the first days after presumed arrival and longer staying individuals remained weight constant. On the contrary, Ovenbirds which travel further south and can be considered long range migrants, showed a marked decrease in body weight soon after arrival. Long-staying individuals of this species stay constant in weight. Finally, White-throated Sparrow, an overwintering species, showed a trend of weight increase after more than 5 days from initial recapture. These findings suggest that overwintering and short-range migrants appear to benefits from isolated urban green habitats while long-range migrants might not.
