Negative effects of wind speed on individual foraging performance and breeding success in little penguins
Résumé
Most effects of environmental and climate variability on predator life history traits and population dynamics result from indirect effects mediated through the food chain. There is growing evidence that wind strength might affect seabirds while foraging at sea. Here, we investigated the effect of wind speed on the foraging performance of a flightless marine predator, the little penguin (Eudyptula minor). To this end, we used satellite-derived wind data collected over 11 breeding seasons during which the daily attendance and body mass changes of more than 200 penguins breeding at Phillip Island (Victoria, Australia) were recorded by an automated penguin monitoring system. Over 17 363 foraging trips, we found that wind speed had important effects on foraging and provisioning parameters in breeding adults. During incubation and chick-guard, stronger winds were associated with decreased foraging efficiency (lower body mass gain). During chick-guard, stronger winds were furthermore associated with lower meal sizes provided to the chicks, but parental body reserves appeared unaffected. Under extreme wind conditions (>14 m/s) during the post-guard phase, adults maintained their body reserves by shifting towards longer foraging trips, while providing chicks with smaller meals. Chick meal size and foraging trip duration during chick rearing had direct effects on breeding success, suggesting that the influence of wind on individual fitness was mediated by changes in foraging performances and success. Furthermore, using a long-term wind data series spanning 150-yr from a coastal wind station, we found a slight decline in wind speed and a decrease in wind speed variability in the Bass Strait where little penguins forage. Interestingly, based on this wind data, we found birds to be more directly affected by punctual events of strong winds (e.g. storms or gales), than by an overall change in wind patterns over time. Potential candidate mechanisms mediating the effects of wind speed on foraging efficiency may include swell formation, energy costs of travelling and thermoregulation, and a possible disruption of thermoclines, which may be important for little penguins. Plasticity in foraging strategies allowed parents to partially compensate for negative wind effects.