CONICET | Buscador de Institutos y Recursos Humanos

We evaluated the distribution and size of Magellanic penguin (Spheniscus magellanicus)colonies in northern San Jorge Gulf, Argentina, characterizing nesting habitat at 14 islands with colonies (IC) and 28 islands without nesting penguins (INC). Digital analysis of a Landsat TM satellite image and field measurements were used to assess vegetation and substrate. The 14 breeding colonies ranged in size from 13 to 96,300 nests. The total penguin population at all colonies was estimated at 218,460 pairs. Colonies were only located on islands. Digital analysis of the satellite image showed that the proportion of area with shrub-steppe vegetation was significantly higher at IC than at INC (38.6 vs. 4.9%), while the percentage of rocky substrate was lower at IC (33.6 vs. 64.8%). The percentage of vegetation cover was positively correlated with island area and with the number of breeding pairs. The probability of finding colonies on islands with shrub-type vegetation was significantly higher than on islands without vegetation or with no shrub-type vegetation. Most nests (98.6%) were located under bushes, while the rest were burrows dug into the substrate. Mean size of bushes used for nesting was higher at IC (4.47 vs. 0.99 m2) as was the percentage of silt-clay substrate (47.31 vs. 1.98%). Coast minimum slopes at INC were steeper than the slopes of entrance routes at IC (27.6 vs. 5.7º). In the northern sector of San Jorge Gulf, Magellanic penguins selected islands with shrub-type vegetation and soil that allow building nests with adequate cover. These results are consistent with the belief that vegetation cover is an important nesting requirement for Magellanic penguins, and the distribution and abundance of this species may be partly dependent on particular habitat features.

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