DOI: 10.5061/dryad.8sf7m0d27
title: Data from: Breeding site departure and post-departure movement strategy in Vireo olivaceus (Red-eyed Vireo)

description: Few studies have been able to assess the decision-making process behind
 migratory departures from the breeding site and the extent to which
 extrinsic cues that favor departure from fall stopover sites also apply to
 initial departure from breeding sites. Factors influencing departure may
 vary between species that first make short-distance regional movements vs.
 those that immediately begin long-distance migration, but for most
 migratory songbirds, it is unknown which post-departure movement strategy
 they use or why. We used an automated radio telemetry network to track
 adult male Vireo olivaceus (Red-eyed Vireo) as they departed their
 northwest Pennsylvania breeding site on fall migration to determine their
 post-departure movement strategy. We also assessed how local weather
 conditions, including surface pressure, humidity, precipitation, and wind,
 influenced the probability of departing the breeding site on fall
 migration. For the individuals for whom we could confidently ascertain
 departure day and time, 86% departed during the first 2 hr after sunset.
 Net displacement was positive, and birds headed directly south towards
 Florida. Birds were more likely to depart on nights with rising surface
 pressure and high humidity, and frequently departed in unsupportive wind
 conditions (headwinds). Our results suggest that V. olivaceus initiates
 true long-distance migratory flights after departing from its breeding
 sites. Birds may have departed under unsupportive wind conditions due to
 the scarcity of tailwinds at the breeding site. Alternatively, birds
 leaving their breeding areas in the fall may be less selective of optimal
 weather conditions for departure than birds departing stopover habitats,
 as they have higher fuel loads and ample time to compensate during the
 rest of their migratory journey.
description: # Breeding site departure and post-departure movement strategy in *Vireo
 olivaceus* (Red-eyed Vireo) Dataset DOI:
 [10.5061/dryad.8sf7m0d27](10.5061/dryad.8sf7m0d27) ## Description of the
 data and file structure Weather variables influencing migratory departure
 decisions for 22 Red-eyed Vireos. ### Files and variables #### File:
 Horn_et_al_2025_data.csv **Description:** Dataset for Cox proportional
 hazards models to assess how weather variables influence the probability
 of birds departing the breeding site on fall migration.  ##### Variables *
 ID: tag number for each bird * status: 0= did not depart, 1=departed *
 year: 2020 or 2021 * detect.date: dates during the migratory period that
 each bird did not depart, up until their actual departure date *
 detect.time: time of migratory departure * start.time: start time for Cox
 model calculation * end.time: end time for Cox model calculation *
 depart.day.of.year: day of year that each individual departed on migration
 * surface.pressure.trend: surface pressure trend in the 24 hr prior to
 departure (Pa/hr) * average.relative.humidity: average relative humidity
 in the 3 hr prior to departure (%) * wind.profit: wind profit at the hour
 of departure * wind.profit.class: wind profits greater than 0.5 were
 classified as ‘tailwinds’, those less than -0.5 were classified as
 ‘headwinds’, and middle values were classified as ‘minimal winds’ *
 rain.class: when the rate of precipitation in the hour of departure was
 less than 0.5 mm, it was classified as ‘trace or no precipitation’, with
 anything higher being classified as ‘rain’ ## Access information Other
 publicly accessible locations of the data: * All Red-eyed Vireo detection
 data from the Motus Wildlife Tracking System (Project 326) are available
 at [www.motus.org](http://www.motus.org) Data was derived from the
 following sources: * Hourly weather measurements for the breeding site
 were retrieved from the ERA5-Land dataset (Muñoz-Sabater et al.
 2021). Weather variables used in the models were transformed using the
 original hourly weather measurements (as per the methods text in Horn et
 al. 2025) and thus are derived values from the ERA5-Land dataset. CDS
 catalogue entry: Copernicus Climate Change Service (C3S)(2019): ERA5-Land
 hourly data from 1950 to present. Copernicus Climate Change Service (C3S)
 Climate Data Store (CDS). DOI:
 [10.24381/cds.e2161bac](https://doi.org/10.24381/cds.e2161bac) (Accessed
 2024)