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 1^st 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.

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.

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