Previous laboratory studies have demonstrated the role of photoperiod in cueing the migration timing of small land birds; however, how migration timing of young birds in wild environments develops in relation to these cues have rarely been investigated. Such investigations can make important contributions to our developing understanding of the phenotypic plasticity of migration timing to new conditions with climate change, where changes in the timing of nesting may expose juvenile birds to different photoperiods. We investigated the impact of manipulating photoperiod during nestling development in a long-distance migratory songbird on the timing of post-breeding movements in the wild. Using programmable lighting installed in the nest-boxes of purple martins (Progne subis), we exposed developing nestlings, from hatch to fledge date, to an extended photoperiod that matched the day length of the summer solstice in Manitoba, Canada. We found that birds with a simulated, earlier photoperiod had a longer nesting period and later fledge and autumn departure dates than control group birds. This study demonstrates the phenotypic plasticity of first-year birds to the ontogenetic effect of their hatch date in the formation of the timing of their first post-breeding movements. Further, we discuss how these results have implications for the potential use of assisted evolution approaches to alter migration timing to match new conditions with climate change.

The dataset was collected during a breeding season of purple martin in Manitoba 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 Proceedings of the Royal Society B.

date: the date of mounting tags on birds

location: location of breeding colonies of purple martins

cavity ID: the number of each nest cavity

Motus:Motus tag number

motustagID: the ID of each Motus tag

treatment: two groups of extension light and control group

t: giving numbers as codes to different groups

first egg date: the date of the first egg of each cavity

hatch date: the date of hatching eggs at each nest cavity

Fledge date: the date of fledging of juveniles of each cavity

Colony departure: the date of juveniles departed their colony

nesting period: duration of nesting period of juveniles 

duration of staying at the colony: the duration between fledge date and colony departure date

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

tail: the length of the tail 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

nestmate numbers: number of nestlings at each nest cavity at the time of mounting tags

site: giving numbers as codes to different sites