Long-term changes in arrival timing and site functionality in two passerine species during spring migration in northeastern Pennsylvania, USA

Abstract

. Although there is abundant evidence that migrant landbirds have modified their migratory timing in response to climate change, few studies have looked for evidence of long-term changes in site use or function, while even fewer studies have looked for differential effects on demographic groups within a species. Here, we analyze 18 years of daily weather data and 17 years of Gray Catbird ( Dumetella carolinensis ) and Common Yellowthroat ( Geothlypis trichas ) capture data to look for evidence of long-term changes in temperature and precipitation as well as arrival timing by species, sex, and age during spring migration in northeastern Pennsylvania, USA. We also determined whether there was evidence of protandry in Gray Catbirds, a sexually monochromatic species. Additionally, we investigated changes in site use, as indicated by long-term change in capture rates or rates of mass gain by age or sex in both species. Although average daily temperatures did not change, we found long-term changes in the amount and probability of precipitation during the spring migratory period (April–May). We also found that both species advanced their arrival timing (Gray Catbirds ~6.6 d/decade, Common Yellowthroats ~2.8 d/decade) and that advances in arrival timing varied by sex or age in both species. We found no evidence of protandry in Gray Catbirds. Further, we found evidence that site functionality changed for both species, as demonstrated by sex-related differences in yearly mass gain for birds using the study site. Understanding the phenological response of migratory species to climate change requires consideration of climate change effects across multiple temporal and geographic scales, and, as our results suggest, consideration of differential effects of climate change by demographic groups within species