Behavioral traits vary with intrinsic factors and impact local survival in Song Sparrows (Melospiza melodia)

Food acquisition is critical for individual fitness. Recent work has highlighted the importance of behavioral traits, such as boldness, for explaining variation in foraging abilities within populations. Greater flexibility in these behavioral traits might help populations persist in the face of environmental change; this may be particularly important for small populations that are more susceptible to local extirpation. We performed a winter-feeding experiment in an extensively studied island population of Song Sparrows (Melospiza melodia) to examine if intrinsic factors (age, sex, and inbreeding) explain variation in behavioral traits (neophobia, boldness toward predators, boldness toward competitors, and aggression) and how behavioral traits influence the probability of local survival for adults and of no dispersal and survival for juveniles. Our results showed that adults were less neophobic and bolder toward competitors than juveniles. This suggests that juvenile Song Sparrows might be more vulnerable to environmental changes than adults and may help explain why juvenile survival has been more strongly impacted by a new competitor on the island. Females were less neophobic than males, indicating that the sexes vary in their behaviors associated with resource acquisition, potentially due to constraints associated with reproduction in females. We found that the individual inbreeding coefficient did not appear to influence any of the behavioral traits examined here. Lastly, more neophobic adults were found to be more likely to survive to hold a territory the following breeding season, demonstrating the consequences of behavior on future fitness. These findings highlight that behavioral traits impact resource acquisition and fitness, and, thus, variation in these behaviors may play a critical role in understanding and predicting how populations respond to environmental change.