Particular aspects of the reproductive biology and population trends of Magellanic Penguins (Spheniscus magellanicus) at Cabo Vírgenes colony, Santa Cruz Province, Argentina

Abstract

We studied Magellanic Penguins (Spheniscus magellanicus) at Cabo Vírgenes colony, Santa Cruz province (52° 22' S, 68° 24' W). During three breeding seasons (1989/90, 1990/91 and 1991/92) we monitored the reproductive biology, and, by adding the following three seasons (1992/93, 1993/4 Y 1994/95) we studied the population trend of this colony. We followed almost 160 active nests each breeding season, from the egg laying period (October) to the fledging period (end of January). To study mean density and nest occupation throughout years, we used 100 m2 plots. Egg laying time was quite invariable between years and laying was rather synchronized. Breeding cycle was shorter than the one described for Punta Tombo. The incubation period was longer at Cabo Vírgenes while the nestling period was much longer at Punta Tombo colony. These two colonies are located almost in the extreme points of the geographic distribution, and differences in environmental conditions could affect their breeding cycles. We present some hypotheses to explain such differences. Based on ringing information, we found Cabo Vírgenes penguins migrating north, reaching the south coast of Brazil. We found no evidence of a southern migration route.