Chough (Pyrrhocorax pyrrhocorax) Science Article 2
The breeding abundance of Choughs Pyrrhocorax pyrrhocorax was investigated in relation to type of rock and related features of nesting cliffs along rivers in south-eastern Madrid (Central Spain). Gypsum cliffs are larger and provide more nest sites than clay and limestone cliffs. Cliffs used by breeding Choughs contained more available nest sites per length than unoccupied cliffs, but this was mainly due to the greater height of the occupied cliffs, since the number of available nest sites per area did not differ. Large cavities and crevices, which were also used as communal roosting sites, were positively selected. Most of the variation in breeding density could be explained by variation in the availability of nest sites in general, and of large caves and crevices in particular. When nest-sites are widely available, positive selection for cliffs that allow a clumped distribution of nests might result in aggregated breeding and a social organization needed for exploitation of feeding resources around cliffs. So it is the high nest-site availability that allows Choughs to occur at densities much higher than those recorded in montane areas in the Mediterranean and in coastal areas of northern Europe. This implies that the role of nesting habitat in the social organization, population dynamics and conservation of Choughs differs between areas
Blanco G., Cuevas J.A. & Fargallo J.A, ARDEA 86 (2): 237-244.