A. Radl et Bm. Culik, Foraging behaviour and reproductive success in Magellanic penguins (Spheniscus magellanicus): a comparative study of two colonies in southern Chile, MARINE BIOL, 133(3), 1999, pp. 381-393
During the breeding season 1996/97 we compared the foraging and diving beha
viour of adult Magellanic penguins (Spheniscus magellanicus), growth rates
of their chicks and their breeding success at two colonies in the south of
Chile. One of the colonies is located on Magdalena Island in the Strait of
Magellan, where a commercial fishery existed several years ago; the other,
on the shores of the yet unexploited Otway Sound. Thirty adult Magellanic p
enguins were equipped with time-depth recorders (TDR) to investigate their
behaviour at sea. In each colony 15 adults returning from the sea were stom
ach flushed to analyse dietary composition. Chicks of TDR-nests and of 12 a
dditional control nests were weighed regularly. Foraging effort was signifi
cantly higher at Magdalena than at Otway. The Magdalena-birds usually remai
ned at sea overnight and foraged with a mean duration of 18 h, whereas the
penguins of Otway Sound foraged during 1-d trips with a mean duration of on
ly 9 h. Compared to Magdalena, penguins at Otway dived shallower (mean dept
h 14.9 vs 16.5 m), shorter (mean duration 57.8 vs 64.3 s) and showed more s
earching and feeding as opposed to travelling activity ton average 69 vs 55
%) during the foraging trips. Compared to other breeding locations both col
onies were characterised by high chick growth rates, high fledging body mas
ses (>3 kg) and early fledging date (after 70 to 80 d), and a very high rep
roductive success of >1.75 chicks per breeding pair. Comparison of the diet
(almost exclusively sprats) with former investigations suggests for both a
reas an unchanged food structure over the last decade. The results in both
colonies indicate ample food availability in the season 1996/97. However, c
ompared to the much smaller Otway colony, penguins on Magdalena have to cop
e with more competition for food. Therefore, future prey limitation, throug
h resumed fishery operations or effects of El Nino, might affect the pengui
n population on the island more negatively than in Otway Sound.