Factors associated with arrival timing and condition of migrant landbird species in northeastern Pennsylvania

Abstract Extrinsic and intrinsic factors operating during and prior to the passerine spring migratory period have been associated with both migratory timing and condition. Here we take advantage of a long-term data set to answer questions about how extrinsic factors encountered on the wintering grounds (El Niño Southern Oscillation, ENSO) and en route (temperatures south of our study site) along with intrinsic factors (age, sex if possible) influenced both arrival timing and condition at our site in northeastern Pennsylvania. Older birds preceded younger, male Common Yellowthroats (Geothlypis trichas) preceded females and within a year later arriving Gray Cat-birds (Dumetella carolinensis) and Common Yellowthroats were in better condition. We found that Gray Catbirds and Common Yellowthroats migrating during warmer years arrived in better condition. Finally, we found evidence that ENSO, likely via influencing weather and food availability during the winter, was associated with arrival timing in Veery (Catharus fuscescens), Common Yellowthroats and possibly Gray Catbirds. Our results support the hypothesis that events experienced earlier, either between (wintering to migratory periods) or within (earlier vs. later in migration) phases of the avian annual cycle may carry over, influencing fitness later in time or in subsequent phases of the annual cycle.