Satellite tracking of Humboldt penguins (Spheniscus humboldti) in northern Chile

During the El Nino of 1982/1983, the Humboldt penguin population diminished dramatically in the whole distributional area of the species. Recovery of the population was slow since 1983 and it has been suggested that large numbers of Humboldt penguins die at ,sea, entangled in nets, or starve to death, even during non-''EI Nino'' years. We were able to determine for the first time, how Humboldt penguins on Pan de Azucar Island (26 degrees S; 72 degrees W) utilize their marine habitat and where their feeding areas lie. For this purpose we employed two streamlined Argos satellite transmitters during the 1994/1995 and 1995/1996 breeding seasons, respectively. Mean travelling speed of Humboldt penguins during foraging trips was 0.94 m s(-1) and 50% of bird positions were located within 5 km of the island (90% within 35 km). Total area covered by Humboldt penguins foraging from Pan de Azucar Island was 12255 km(2). Satellite transmitters also recorded dive duration; penguins spent on average 7.8 to 9 h diving per foraging day but. showed no preferences for particular feeding areas. Mean daily dive durations (4-d mean) recorded during the 1994/1995 breeding season were positively correlated between birds. Significant correlation between dive duration and sea surface temperature anomalies and negative correlation between dive duration and fishery landings at nearby Caldera harbour indicate that the 1994/1995 increase in foraging effort was a response to deteriorating prey availability. Sea surface temperatures during the 1995/1996 breeding season were colder than average, and we observed no trends in bird diving activities.