Variation in Nestling Body Condition and Wing Development at Fledging Predict Post-fledging, Cause-specific Mortality in the Dickcissel (Spiza americana)

Phenotypic traits developed in one life history stage can carryover and affect survival in subsequent stages. Such carryover effects may therefore be critical for survival during important periods of an animal’s life; such as the juvenile life history stage. For songbirds, carryover effects from the pre-to post-fledging period may be crucial for survival but are poorly understood. We assessed whether juvenile body condition and wing development at fledging influence survival during the post-fledging period for fledgling Dickcissels (Spiza americana) in east-central Illinois, USA. We found pre-to post-fledging carryover effects on fledgling survival for both traits during the early part of the post-fledging period. Survival benefits of each trait were conditional upon cause-specific sources of mortality; individuals in better body condition were less likely to die from exposure, whereas those with more advanced wing development were less likely to be preyed upon. Fledglings with more advanced wing development were also comparatively more active and mobile earlier in the post-fledging period, suggesting they were better able to avoid predators. Our results provide some of the first evidence linking development of juvenile phenotypic traits to survival against specific sourcesof post-fledging mortality in songbirds. Further investigation of pre-to post-fledging carryover effects may provide important insights into avian life history evolution.