Hatching failure is greater in altricial bird species with cavity nests and large clutches

Abstract

Abstract Mortality rates are high for most avian species during early life stages, forming a critical source of natural selection that helps shape the diversity of avian life-history traits. We investigated hatching failure (i.e., non-predatory embryonic mortality, excluding abandoned or damaged eggs) and found significant variation among passerine species. Failure rates ranged from 1.0% to 12.7%, and species with cavity nests and larger clutches experienced greater rates of hatching failure. While past research has focused on the direct effects of predation on the nestling and fledgling stages, little is known about how predation may indirectly influence other sources of mortality such as hatching failure. We investigated the influence of nest predation risk and other factors on variation in hatching failure among 14 free-living grassland and shrubland songbird species. Across all species, 7.7% of 1,667 eggs failed to hatch. We found little evidence that variation in nest temperature influenced rates of hatching failure within and among species, although species with larger clutch sizes had more variable nest temperatures. Dissection of failed eggs revealed that most hatching failures occurred before or shortly after the onset of development; however, there was no difference between cavity and open-cup nesters in the rate of early-stage mortality. Our findings suggest there may be tradeoffs to having a large clutch, with a benefit of rearing more young at the cost of greater hatching failure, possibly due to delayed onset of incubation, poor incubation behavior, or inability to incubate large clutches. Additionally, as larger clutches are often laid in cavity nests, which have a relatively low predation risk, this may outweigh the costs of increased hatching failure. More experimental approaches, such as clutch size manipulations and egg-specific incubation behavior are needed to provide greater insight into factors driving variation in hatching failure across species.