Should I breed or should I go? Manipulating individual state during migration influences breeding decisions in a long-lived bird species

1.Documentation of carry-over effects (COEs), defined as effects resulting from events that occurred in a previous time period, has largely been observational and understanding of specific mechanisms underlying COEs is still lacking. To investigate this, we simulated an environmental perturbation during the spring migration of a long-lived bird species and looked at the subsequent effects on various breeding parameters.2. We captured female greater snow geese Anser caerulescens atlanticus on their spring staging sites and maintained individuals in captivity for up to 4 days before releasing them. We re-observed females 3000 km North, on their Arctic breeding grounds, to estimate their breeding propensity (i.e. probability of initiating a reproductive event for a given year), and measured their arrival date, laying date, clutch size and nesting success.3. Only proxies of breeding propensity were affected by our manipulation, which decreased as the time spent in captivity increased. However, females were able to overcome the effects of captivity in two out of the 3 years of experimentation with normal or good environmental conditions at the breeding site.4. When facing the additional challenge of poor environmental conditions, many individuals manipulated during migration apparently curtailed their reproductive effort by skipping breeding. This experiment is the first to show that breeding propensity is an important parameter affected by COEs resulting from stressful events prior to reproduction in long-lived species.

Automated summary

This study investigates the effects of environmental perturbation during spring migration on subsequent breeding parameters in a long-lived bird species. The results show that only breeding propensity is affected by the manipulation, and individuals can overcome the effects under normal or good environmental conditions at the breeding site.