Effects of Breeding Phenology on Age‐Specific Mortality in a Threatened, Cooperatively Breeding Songbird

ABSTRACT

Age‐specific mortality is an important source of natural selection shaping life histories among animal taxa. Despite the importance of age‐specific mortality, few studies have provided robust estimates as to the timing and concentration of mortality across the annual life cycle of birds, nor the factors influencing them. We leveraged two long‐term population studies on the threatened Florida scrub‐jay ( Aphelocoma coerulescens ) to examine patterns of age‐specific mortality across the full annual life cycle for the species, from an egg to second year, to test whether patterns in age‐specific mortality varied with the timing of breeding. Stage‐specific survival varied across life stages and between the two populations, with survival generally increasing across life stages within populations, but combined, survival was roughly equivalent as offspring progressed from an egg (58.9%), to nestling (58.7%), to fledgling (58.4%), to juvenile (60.5%), and to first‐year adult (60.9%). More than 90% of offspring mortalities occurred prior to recruitment (nest, post‐fledging, and juvenile stages). We also found a negative association between the timing of breeding and age‐specific mortality from fledgling up until recruitment—including the post‐fledging and juvenile life stage, but not first‐year adults—and past research has shown similar trends with nest survival, suggesting breeding productivity of scrub‐jays declines across the breeding season. Our findings help to advance our knowledge of avian life history theory and concur with past research recommending management that aims to improve scrub‐jay offspring survival, particularly during the early breeding season, such as use of prescribed fire and protecting early nests.