Breeding biology of Magellanic Penguins (Spheniscus magellanicus) at the Beagle Channel: interannual variation and its relationship with foraging behaviour

Abstract

Interannual variation in seabird foraging or reproductive behaviour may reflect fluctuations in marine resources. In this study, we evaluated different foraging and breeding parameters of Magellanic Penguins (Spheniscus magellanicus) from Martillo Island in the Beagle Channel, and the relationships between these parameters at different stages within the season (incubation, early and late chick-rearing) over three consecutive breeding seasons (2006–2007, 2007–2008 and 2008–2009). In 2007, we observed greater adult foraging effort (longer foraging trip duration and vertical travel distance, VTD) and lower chick feeding frequency, together with a slower growth rate and later fledging date of chicks, which we suggest was linked to lower food availability near the colony that year. The increased foraging effort appeared to be compensated by enhanced feeding activity (e.g., number of wiggles per dive). However, this increase did not coincide with a larger amount of food load brought to colony, which may have been due to a change in the type or size of prey consumed by the penguins. Magellanic Penguins from Martillo Island showed great plasticity in foraging behaviour, as evidenced by changes in consumed prey type or increased foraging effort and feeding activity when the consumption of their main prey item, Sprattus fuegensis, seemed to decrease. Moreover, during this particular breeding season, although the growth rate of chicks was lower, the breeding success remained constant throughout the study period, suggesting that the penguins managed to compensate for the apparent decrease in Fuegian sprat.