Potential drivers of differences in breeding phenology as a component of life history strategies among coexisting species

Breeding phenology can have strong demographic consequences. Yet, the
reasons why coexisting animal species differ in breeding phenology have
received little attention. We tested selection pressures that underlie
life history variation, such as age-specific mortality, diet, and body
size to explain the breeding phenology of 16 coexisting songbird species
in arid shrubland in South Africa. The average start and end dates for the
earliest and latest species differed by 1.5 months, with a gradient among
the remaining species. Nest predation risk generally increased through the
season, although species differed in seasonal patterns. Species with lower
annual adult mortality, greater seasonal increases in nest predation, and
greater nest predation rates had earlier start and stop dates, thereby
reducing demographic risks. Species with higher adult mortality had larger
brood sizes that required more food and they bred later when food was more
abundant. Evolved timing of breeding thereby reflecting risk management
and food availability related to longevity and brood size. These factors
may place unrecognized constraints on within-species responses to climate
change. Given the importance of phenology for fitness, phenology should be
integrated as a core life history trait in future theory, and evolutionary
constraints need to be considered in responses to climate change.