DOI: 10.5061/dryad.40jm7
title: Data from: Migration timing and its determinants for nocturnal migratory birds during autumn migration

description: 1. Migration is a common strategy used by birds that breed in seasonal
 environments, and multiple environmental and biological factors determine
 the timing of migration. How these factors operate in combination during
 autumn migration, which is considered to be under weaker time constraints
 relative to spring migration, is not clear. 2. Here, we examine the
 patterns and determinants of migration timing for nocturnal migrants
 during autumn migration in the north-eastern USA using nocturnal
 reflectivity data from 12 weather surveillance radar stations and modelled
 diurnal probability of occurrence for 142 species of nocturnal migrants.
 We first model the capacity of seasonal atmospheric conditions (wind and
 precipitation) and ecological productivity (vegetation greenness) to
 predict autumn migration intensity. We then test predictions, formulated
 under optimal migration theory, on how migration timing should be related
 to assemblage-level estimates of body size and total migration distance
 within the context of dietary guild (insectivore and omnivore) and level
 of dietary plasticity during autumn migration. 3. Our results indicate
 seasonal declines in ecological productivity delineate the beginning and
 end of peak migration, whose intensity is best predicted by the velocity
 of winds at migration altitudes. Insectivorous migrants departed earlier
 in the season and, consistent with our predictions, large-bodied and
 long-distance insectivorous migrants departed the earliest. Contrary to
 our predictions, large-bodied and some long-distance omnivorous migrants
 departed later in the season, patterns that were replicated in part by
 insectivorous migrants that displayed dietary plasticity during autumn
 migration. 4. Our findings indicate migration timing in the region is
 dictated by optimality strategies, modified based on the breadth and
 flexibility of migrant's foraging diets, with declining ecological
 productivity defining possible resource thresholds during which migration
 occurs when winds at migration altitudes are mild. These observations
 provide the basis to assess how avian migration strategies may be affected
 by adjustments in seasonal patterns of atmospheric circulation and
 ecological productivity that may occur under global climate change.
description: STEM_probability-of-occurrenceWeekly estimates of probability of occurrence for 142 migratory species within 37.5 km radius circles centered on 12 weather surveillance radar stations located in the northeastern USA . Estimates are derived from spatiotemporal exploratory models (STEM) with occurrence information from the eBird citizen science dataset for the combined period 2004 to 2011.WSR_station_reflectivityDaily total effective scattering area (reflectivity) of birds (square centimeters) per unit volume (cubic km) estimated at 12 weather surveillance radar (WSR) stations in the northeastern USA during the autumn of 2010 and 2011 within 37.5 km radius of each WSR station and up to a maximum altitude of 3 km above ground level.