DOI: 10.5061/dryad.6djh9w12s
title: Does hatch date set the clock? Timing of post-fledging movements for families of a colonially breeding, long-distance migratory songbird

description: Factors that influence the development of migration timing in juvenile
 songbirds have implications for the ability of individuals to respond
 positively to rapid environmental changes. We investigated the impacts of
 nest timing on the post-fledging movement timing of juveniles and adults
 of a migratory songbird. We tested whether first egg date and
 environmental factors predicted the initiation of post-fledging stages:
 fledge date for juveniles, and colony departure date for both adults and
 juveniles. At breeding colonies of purple martin (Progne subis) in
 southern Ontario, Canada, we monitored nests to determine the date of nest
 initiation (‘first egg date’) and deployed 122 coded radio-frequency
 tracking tags on young and adults to determine the timing of post-fledging
 stages. We found that first egg date, the number of nestmates and age of
 parents were the main predictors of fledge date. Of these three factors,
 only first egg date was carried through post-fledge to influence colony
 departure date for juvenile birds, but this relationship weakened between
 first egg date and departure date. Nestmates tended to fledge together
 (range 0-4 days) but exhibited greater variation in colony departure
 timing (range 0-11 days). Further, while first egg influenced departure
 date, increasing variation between fledge and departure led to some birds
 departing breeding colonies at a younger age, suggesting in influence of
 local environmental factors (e.g. social or photoperiod change) in
 departure decisions. The timing of adult colony departure date was
 independent of first egg dates. In sum, our results suggest a role for 1st
 egg dates in setting timing of post-breeding movements, but with variation
 introduced between fledge and departure dates. Experimental manipulations
 of photoperiod in a wild setting are needed and future research should
 investigate whether the timing of movement driven by nesting timing, holds
 across the rest of migration or even the lifetime of birds.
description: The dataset was collected during a breeding season of purple
 martin at three breeding colonies in different locations in Ontario and
 has been processed by a series of generalized linear mixed models (R v.
 3.6.1) to produce a MS accepted for publication in the Journal of Avian
 Biology.
description: Cal: tag ID: the ID of each Motus
 tag date: the date of mounting tags on birds
 sex: undefined for juveniles and  cavity : the
 number of each nest cavity hatch date: the date of
 hatching eggs at each nest cavity first egg date: the
 date of the first egg of each cavity Age: age of birds
 at the time of mounting tags Fledge date: the date
 of fledging of juveniles of each cavity dcdoy: the date
 of colony departure date in number of days of a year of juveniles of each
 cavity nesting period: duration of nesting period of
 juveniles  age at fledge date: age of bird at fledge
 date  age at colony departure date: age of bird at
 colony departure date datan: date:
 the date of mounting tags on birds mfgID: Motus tag
 number tagID: the ID of each Motus tag
 age1: 1 indicates adult and 2 indicates juveniles 
 sex: undefined for juveniles and F indicates female and M
 indicates males cavity ID: the number of each nest
 cavity age: HY indicates for juveniles and ASY
 indicates after the second year and SY indicates the second year
 nestlings: number of nestlings in a cavity
 first egg date: the date of the first egg of each
 cavity location: location of breeding colonies of
 purple martins ageA: age of birds at the time of
 mounting tags age at fledge date: age of bird at fledge
 date  site: giving numbers as codes to different
 sites Fledge date: the date of fledging of juveniles of
 each cavity Colony departure: the date of juveniles
 departed their colony weight: the weight of juveniles
 at the time of mounting tags on them tarsus: the length
 of the tarsus of juveniles at the time of mounting tags on them
 wing: the wing length of juveniles at the time of mounting tags
 on them fat: the score of fat of juveniles at the time
 of mounting tags on them year: different years of
 study