Indicators of and Influences on Reproductive Success in Yellow-eyed Penguins (Megadyptes antipodes)

Abstract

Reproductive success is highly variable among individuals in bird populations and is often attributed to differences in individual quality. A small percentage (5.4%) of the endangered yellow-eyed penguin (Megadyptes antipodes) population at Boulder Beach, New Zealand, appears to contribute many more offspring to future generations compared to other individuals. To date, these high quality yellow-eyed penguins can only be identified retrospectively, using breeding data collected over their entire lifetimes. Yellow-eyed penguin numbers are dwindling as a result of numerous stressors, despite conservation management. Therefore, identifying potential indicators that would allow the superior breeders to be distinguished from average breeders would help guide yellow-eyed penguin management with respect to prioritising assistance for particularly productive breeding pairs. Immunocompetence and feather ornamentation are well studied in birds as measures of reproductive fitness and are influential in sexual selection. Two common parameters used to infer levels of fitness are oxidative stress levels and leucocyte counts. These components of immunocompetence are obtained through haematological analyses and provide an idea of the individual’s ability to resist infection (oxidative stress levels) and their stress levels (leucocyte counts) at the time of sampling. Ornament brightness, colour, and size are all widely known indicators of quality as well. I examined these parameters in relation to both short- and long-term reproductive success. In addition to this, I used 11 microsatellites to estimate internal relatedness (IR), which is a measure of inbreeding, to understand whether inbreeding levels influenced any of the putative indicators or was linked to reproductive success. I found that superior breeders had higher levels of oxidative stress in their lifetime: this means that despite experiencing more challenging events, there were able to successfully fledge more chicks. The superior breeders were also less stressed (Heterophil/Lymphocyte ratio) in relation to the number of eggs laid for the year. Variation in the ornamentation parameters was not associated with differences in reproductive performance. Inbreeding did not have a significant effect on the indicators, which is good for the yellow-eyed penguin population since inbreeding levels are not affecting the reproductive success of these birds. This study shows that there are two promising indicators to discern breeding quality in yellow-eyed penguins (oxidative stress and H/L ratios), and that inbreeding levels are not currently a concern.