ABSTRACT
Abstract. Recent research has shown that bird species are responding to changes in temperature and that spring migrations are shifting earlier for many species. Much less research has examined if and how fall migrations are changing, particularly in the United States. Here, we present an analysis of fall migration for 37 species of landbirds captured over a 44-year period at Manomet Center for Conservation Sciences in Manomet, Massachusetts. In the years 1969-2012, migration cohorts of 28 species significantly declined in abundance and two increased. For 14 species, the mean dates of fall passage at Manomet changednine migrated later and five earlier. Over this time span, the mean temperature of the region during the months of August and September has warmed. Fall passage dates for 14 species were correlated with temperature-13 species tended to migrate later with warmer temperatures and one species
migrated earlier. We also included fall plant phenology in our analyses-four bird species tended to migrate later when leaf color change is delayed. Linear mixed-effects analysis indicates that species that winter in the tropics migrate earlier in the fall than birds that winter in other areas, and single-brooded species migrate earlier in the fall than double-brooded birds. Patterns of fall migration at Manomet show relatively little correlation with comparable data reported from the banding station at Powdermill Nature Reserve in Rector, Pennsylvania, suggesting spatial variation in the responses of fall migration to a warming climate. It is evident that fall migration dates vary considerably among species and that species are responding in different ways to the changing climate.
