Manipulating individual state during migration provides evidence for carry-over effects modulated by environmental conditions

Abstract

Despite observational evidence of carry-over effects (COEs, events occurring in one season that produce residual effects on individuals the following seasons), to our knowledge no experimental studies have been carried out to explore how COEs might affect reproductive output. We simulated an environmental perturbation affecting spring-staging migrants to investigate COEs in greater snow geese (Anser caerulescens atlanticus). During three consecutive years, 2037 females captured during spring staging (approx. 3000 km south of their Arctic breeding grounds) were maintained in captivity (with or without access to food) for 0-4 days. Duration of captivity (but not food treatment) negatively affected reproductive success, probably through stress response. Reproductive success was reduced by 45-71% in 2 years, but not in a third year with unusually favourable breeding conditions. This unprecedented manipulation indicates that COEs can have a strong effect on individual reproductive success in long-distance migrants, but that this effect can be partly compensated for by good environmental conditions on the breeding ground.

Figure 1.

Mean change in body mass (body mass controlled for body size and date in grams) before versus immediately after treatment for fed (grey triangles) or fasting (open circles) groups maintained in captivity for 2, 3 or 4 days. Error bars represent ±1 s.e.

Figure 2.

Mean reproductive success (probability that a female was resighted in the subsequent autumn with at least one young) in relation to (a) the treatment duration (days maintained in captivity) or (b) with body mass in spring (body mass at capture controlled for body size and date), in 2007–2009. The fitted logistic models (black line when significant and long dashed otherwise) as well as its confidence interval at 95% (stippled line) are shown. Grey circle sizes are proportional to log (N) available for each days of treatment or body mass classes.