“Nesting habitat differences between colonies of southern giant petrel along the Patagonian coast”

S COPELLO; F QUINTANA; A SCHIAVINI; A RAYA REY

Montevideo, Uruguay

Conferencia; III International Albatross and Petrels Conference; 2004

The availability and quality of suitable nesting habitat are important factors determining seabird distribution, abundance and breeding success. In Argentina, the Southern Giant Petrel (Macronectes giganteus, SGP) breeds along the Patagonian coast, in four colonies: I. Arce, 45º 00’S, 65º 29’W, I. Gran Robredo, 45º 08’S, 66º 03’W, Península Lopez, 54º 54’S, 64º 39’W and I. Observatorio, 54º 39’S, 64º 08’W. We present information on habitat characteristics of two colonies located at the north (I. Arce) and south (I. Observatorio) extremes of their breeding distribution along the Patagonian coast. The number of breeding pairs of I. Arce was 300-350 (direct counts), and about 500 pairs (line transects) were estimated in I. Observatorio. The northern colony constituted a dense aggregation of birds (9 nests/100 m2, range 2-25) while the southern colony showed a loose aggregation composed by more than 70 small groups of nest (group mean size= 5.6, range 2-22). The northern colony occupied only 1% of I. Arce (55.8 ha), while the southern colony covered more than 40% of the island (400 ha). Nests at I Arce are located in a rocky outcrop without any kind of vegetation. At I Observatorio, 90% of nests were located over Magellanic moorland, comprised especially of graminoid bogs intermingled with shrubs. The rest of the nests occupied marginal areas of tussock grass. These results highlights the wide range of nesting habitats used by the SGP in all their breeding range.