Temporal, spatial and social segregation of red-billed choughs between twotypes of communal roost: a role for mating and territory acquisition

We assessed the value of communal roosting for mating and territory acquisi tion in nonbreeding red-billed choughs, Pyrrhocorax pyrrhocorax. Between 19 91 and 1996 we surveyed all communal roosts, breeding territories and vacan t nest sites in an area of 250 km(2) in Los Monegros (northeast Spain), as well as other communal roosts in the surrounding 500 km(2) from 1987 to 199 6. Main roosts were used traditionally and throughout the year and gathered more choughs than subroots, which were used only during the nonbreeding se ason. Nonbreeding choughs were socially segregated in these roosts accordin g to their age and breeding prospects. Compared with random potential roost sites, main roosts included more first-year birds and were in areas of hig her breeding density. Subroosts were mainly joined by choughs of breeding a ge (at least 2 years old) whose morphology (males) and body condition (fema les) were similar to those of established breeders, and were in areas with breeding densities as high as around main roosts but with more available ne st sites. Nonbreeding choughs that used main roosts later used subroosts, w hile the converse was rare. More choughs joining subroosts acquired mates t han those joining main roosts. Choughs mostly paired with roostmates but al so with widowed territorial breeders. Finally, choughs from subroosts acqui red territories closer to the roost than those who mated in main roosts, su pporting the hypothesis that subroosts reduce the costs of mating and terri tory acquisition. (C) 1999 The Association for the Study of Animal Behaviou r.