The use of social Stegodyphus spider retreats as nest-lining by pale chanting-goshawks (Melierax canorus): is it about preference?

The pale chanting-goshawk (Melierax canorus) incorporates silk nests (hereafter ‘retreats’) of the social spider Stegodyphus dumicola (Araneae: Eresidae) in the construction of the nest-lining of their own nests. This study investigates whether pale chanting-goshawks in the Little Karoo, South Africa, show a preference for spider retreats as nest-lining and how this preference impacts on the abundance and distribution of Stegodyphus retreats within chanting-goshawk territories. In spite of an average 37 retreats per 2.2 km2 pale chanting-goshawk territory, the birds selected few spider retreats (18 % of those provided during experimental manipulations). The highest proportion of spider retreats (38 %) were found within 223 m of chanting-goshawk nests, probably being moved there over time by nesting birds. Given a choice between sheepskin, active spider retreats, cushion stuffing and cotton waste, the birds preferred sheepskin (53 % by volume) although sheep are not farmed in the study area. These findings demonstrate that the pale chanting-goshawks were searching for soft insulating material to line the nest rather than spider retreats per se.