Delayed start of full incubation is related to a delayed brood patch development in Magellanic penguins

Abstract

Capsule: Most bird species start full incubation before the clutch is complete, others long after laying the last egg, gradually increasing the incubation temperature as incubation progresses, as is the case in Magellanic Penguins Spheniscus magellanicus. Aims: In this study, we analysed the possible mechanisms underlying this delayed start of full incubation in Magellanic Penguins. We postulated two non-mutually exclusive, possible mechanisms: delayed development of the brood patch and/or variation in the adults’ incubation postures. Methods: We conducted our work at Isla Quiroga, Argentina during 2011–13. We measured the development of the brood patch area, its temperature, the egg temperature and observed the postures of adult penguins. Results: We found no association between the adults’ postures and the delayed start of full incubation, nor between brood patch temperature and the increase in egg temperature as incubation proceeded (egg age). The intercept of the curve between egg temperature and egg age was positively related to brood patch area, while the slope of the curve was negatively related. Conclusion: Our results support the hypothesis that the shape of the curve of the increase in egg temperature as incubation proceeds is a consequence of the increase in the extension of the brood patch area.