Foraging trip duration in male and female macaroni penguins at Bouvetøya

The CEMP Standard Methods for monitoring foraging trip duration in Macaroni Penguins recommend using only males. However, males attend the chicks at the nest during most of the brooding period, while the females make frequent foraging trips. We analysed data from 17 males instrumented with VHF-transmitters in the middle of the brooding period (chick age 12-18 days) and 17 females instrumented at the start of the creching period (chick age 25-30 days). Males made their first foraging trips at the start of the creching period. The first trip usually lasted several nights, whereas the subsequent trips were shorter (average 21.8 h). Female foraging trips averaged 27.2 h. No apparent changes in the foraging trip duration of either sex as a function of date were recorded during the creching period. Female attendance periods in the colony where shorter (average 11.9 h) than those of males (average 21.4 h), and females made more foraging trips than males. These results suggest that females might be more appropriate than males as the subjects when monitoring foraging trip duration. In addition, the fact that females spent more time foraging and conducted more foraging trips than males might suggest that female foraging trip duration is more sensitive to changes in prey availability.