Crosswinds During Spring Migration Carryover and Influence the Time Interval Between Arrival and Laying in a Neotropical Migrant.

Events on the non-breeding grounds and on migration can influence the timing of reproduction and the productivity of migratory songbirds. We show, using data from a 12-year study in Revelstoke, BC, Canada, that the onset of breeding in yellow warblers (Setophaga petechia) is linked to weather conditions on migration, specifically the speed of crosswinds experienced over the western flyway during a 2-week period from May 18 to 31. During 2015-2017, we investigated whether this carryover effect was due to crosswind effects on the timing of arrival, the reproductive state and mass of females on arrival, or a combination of other effects that delayed egg laying. In these years, female arrival dates varied with age but were independent of year, growing degree days, or crosswinds on migration. Though crosswinds experienced by females during the 14-day period before their arrival on the breeding ground had no significant effect on their reproductive state (plasma triglyceride levels) or mass (controlling for tarsus length) on arrival, crosswinds had an effect on the time interval between arrival and egg laying. The time interval between arrival and egg laying was also shorter if females arrived with elevated plasma triglyceride levels and longer if females arrived early in the season. Carryover effects from crosswinds experienced during migration on the timing of breeding and reproductive success of yellow warblers are likely to arise due to their effect on arrival date and how rapidly birds can transition from a migratory to a reproductive physiological state. Both wind-speed experienced on migration (14 days before arrival) and reproductive state on arrival (plasma triglyceride concentration) independently influenced the time interval between arrival and egg laying. Crosswinds that delay breeding have a significant effect on reproductive success; female yellow warblers that initiate reproduction late decrease both their chance to raise at least one nestling and the number of nestlings fledged.