Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction). We used 29 years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment). Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before. Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99.5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87.7% for owls with clutches of 1-2 eggs compared to 97.5% for owls with clutches of 4-6 eggs). Overall, our results suggested that changes in extrinsic conditions (predominantly food availability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks) owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.
Juvenile surival: The input file used for the juvenile survival analysis first individual covariate is the standardized connectivity to goshawk nest sites, and the second individual covariate is the standardized distance to the nearest goshawk nest site
Temporal covariates for juvenile survival analysis: Temporal covariates for juvenile survival analysis. The first covariate is the standardized autumn vole density, The second is the standardized local goshawk abundance. The third is the standardized total goshawk abundance. The 4th is the interaction between the 1st and 2nd covariates. The 5th is the interaction between the 1st and 3rd covariate.
breeding propensity analysis data file
breeding propensity analysis.pdf
Clutch size and nest abandonment analysis datafile
Clutch size and nest abandonment analysis.pdf
This work is licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication license.
- Accipiter gentilis
- breeding decisions
- breeding propensity
- juvenile survival
- northern goshawk
- predation risk
- reproductive strategies
- Strix aluco
- tawny owl