The model predicted that residents should have at least 61.25% higher breeding success than migrants.The results provide empirical evidence to help scientist understand how migration evolves and becomes maintained in animal population.These animals include many songbirds, which return to the same habitat in the following spring because it offers abundant resources that are thought to help them to breed more successfully.Yet, migration itself can be risky, and there is little empirical data on the survival benefits of migration in songbirds. tested whether songbirds that migrate are actually more likely to survive the winter than those that do not migrate.Theory predicts that those birds that do not migrate should have some reproductive benefit instead.This makes sense given that birds which remain at the breeding grounds would have access to prime breeding sites which are limited. estimated how much of reproductive benefits the residents would need to outweigh their greater risk of not surviving the winter.The adaptive function of migration has often been hypothesized to be a selective advantage to escape adverse situations caused by seasonal fluctuations of food resources or environmental conditions.This seasonality may impose considerable constraints to life, particularly during the winter season.
To evolve and to be maintained, seasonal migration, despite its risks, has to yield fitness benefits compared with year-round residency.
Recent comparisons of migrant and resident steelheads (Oncorhynchus mykiss) found that female migrants have higher fecundity than females that remain in fresh water streams (Satterthwaite et al., 2009; Hodge et al., 2014, 2016).
Similarly, the noctuid moth (Autographa gamma) performs a multi-generational migration which confer substantial reproductive benefits by allowing a lineage to spread to multiple sites (Chapman et al., 2012).
Using a combination of capture-mark-recapture and radio telemetry, we compared survival probabilities between migrants and residents estimated by multi-event survival models, showing that migrant blackbirds had 16% higher probability to survive the winter compared to residents.
A subsequent modelling exercise revealed that residents should have 61.25% higher breeding success than migrants, to outweigh the survival costs of residency.