Lifetime reproductive success in yellow-eyed penguins: influence of life-history parameters and investigator disturbance

Abstract

Longitudinal studies focusing on lifetime reproductive success (LRS) can be used to measure individual breeding performance, and identify commonalities amongst successful breeders. In some seabird species, it has been shown that a relatively low proportion of individuals actually contribute offspring to the next generation. In yellow- eyed penguins (Megadyptes antipodes), although certain characteristics indicative of poor breeders are known, there has not yet been a comprehensive study of the components influencing lifetime reproductive success. For long-lived species, reproductive decisions are often trade-offs for current and future reproductive success, influenced by many life- history and environmental parameters. Therefore, in a well-studied species, the question arises whether intensive research and monitoring is negatively affecting lifetime reproductive success. Yellow-eyed penguins are known to be vulnerable to human intrusion, and research on this species often warrants the need for handling of birds, eggs, and their young. The aim of this study was to analyse 23 years of yellow-eyed penguin breeding data to determine which life-history components including investigator disturbance, influence lifetime reproductive success in yellow-eyed penguins on the Otago Peninsula, New Zealand. Effects of investigator disturbance were also measured for probability of yearly breeding success and adult survival.

In total, 18.8% of yellow-eyed penguin chicks survived to breed, and 10.3% produced banded offspring. Despite the high juvenile mortality rate of yellow-eyed penguins, the birds that do attempt breeding have high success rates in comparison with other seabird species. The number of recruits and successful recruits produced by individual birds over their lifetimes was strongly related to the number of chicks fledged, showing that the number of lifetime fledglings could be used as an indication of individual fitness. The main factors affecting lifetime reproductive success were lifespan, breeding lifespan, and age at first breeding. Lifespan was the strongest correlate of lifetime reproductive success.

There were no strong effects of investigator disturbance on LRS, probability of breeding success, or adult survival. However, instances of investigator disturbance may affect LRS by artificially reducing the lifespan of birds subjected to intensive regimes of blood sampling and double-banding. This result was found for blood sampling in one of three breeding seasons, and for double-banding in one of two breeding seasons. Investigator disturbance did not affect the most robust individuals in the analysis of LRS, however the nature of the effect on short-lived individuals is unknown. A yearly analysis with the probability of breeding success found that experience and mate experience explained the majority of the variance. While there were some limitations associated with adopting a retrospective approach, the longitudinal aspect of this study identified variation in results between breeding seasons, possibly due to random effects such as the stochastic nature of the marine environment and predation.