Differences in the Quality of Territories Held by Wheatears (Oenanthe oenanthe)

SUMMARY (1) The breeding success of migrant wheatears studied on Skokholm Island, Dyfed, Wales, showed a seasonal decline. The timing of breeding of females was very closely related to the date of their arrival on Skokholm, there being a delay of about 3 weeks between arrival and the laying of the first egg. (2) Certain territories consistently tended to be used by early breeding birds, others by late breeding birds, and this was not due to their occupation, in different years, by the same individuals. (3) The territories in which early breeding occurred were occupied in a greater proportion of the 4 study years. They were also occupied by older (as opposed to first summer) males and they were the first territories to be taken up at the start of the breeding season. (4) I suggest that the territories in which early breeding occurred were those better suited to the wheatear's feeding technique. (5) Feeding rate and time budget data were collected from females in the period from arrival through incubation. It seems that the delay between arrival and laying may not be caused by the need to build up food reserves for egg formation. Instead I suggest that this period may be required for the development of the reproductive organs.