Socio-Ecology of Non-Breeding Choughs, Pyrrhocorax pyrrhocorax

Still, Elizabeth A (1989) Socio-Ecology of Non-Breeding Choughs, Pyrrhocorax pyrrhocorax. PhD thesis, University of Glasgow.

Abstract

Observations of colour-ringed choughs were carried out at communal roosts and feeding flocks. 1. Of the three roosts studied, one was in continual use over the whole year holding from 30 to 120 choughs. The other two roosts were used by family groups after fledging and by young birds over the late autumn and were not in use all year. 2. The numbers of choughs using communal roosts were not static. The highest numbers were during the summer period when the young were fledging. 3. At the roost which was in continual use, numbers of first and second year choughs fluctuated to a greater degree than those of older birds with young birds moving to other roosts during the autumn / winter. 4. At the roost which was in continual use and where detailed observation of individual choughs could be carried out, there was an age-related dominance hierarchy with older birds winning and initiating more aggressive interactions than young birds (particularly first years). The majority of aggressive interactions were settled by threat rather than physical contact. 5. Young choughs arrived in the evening at the communal roost earlier and were less site-faithful in their roosting positions than older birds. 6. There was segregation of age classes within the roost flock during the summer with second nearest neighbours of each age class being of the same age greater than expected by chance. There was no difference from random in the age associations during the winter. 7. Choughs arrived earlier in the evening and at higher light intensities during the summer months than in the winter. The time at which birds arrived at the roost was more closely associated with time before sunset than light intensity. However, settling in the roost was more closely associated with light intensity than time before sunset. 8. Experimental food patches were provided on six occasions during the winter to test the "information centre" hypothesis. Choughs took several hours after dawn to find the bait on the first day but were quick to return after leaving the roost the following day (i. e. within minutes). More birds arrived on the second day. The reason for this is unknown but may be due to birds following others out from the roost, or local enhancement. The fact that choughs quickly returned to the experimental food patch suggests that they are quick to take advantage of newly avaiable food sources especially during the winter. 9. Set route surveys were carried out and the locations of colour-ringed choughs recorded. The areas in which 75% of roosting choughs were found feeding from each roost did not overlap though these discrete "core " areas were not defended. 10. Foraging range from the roost varied seasonally with birds foraging further in the summer. Young choughs foraged further (nearly twice as far) during the winter than older birds. 11. There was no significant difference in the distribution of flock sizes between seasons although in spring and summer the highest proportion of flock sizes being flocks of two. 12. There were differences in the proportions of different age classes in different areas. There were also differences in the proportions of different age classes depending on flock size. In an area where a higher proportion of the population was composed of older choughs, first year choughs tended to be found in smaller flocks especially during the winter. In areas where there were few older choughs present, first year choughs tended to flock together and were found in higher proportions in larger flocks than in an area where there were more older birds. 13. In feeding flocks individual birds' vigilance was related to flock size, decreasing with increasing flock size. For first year choughs however, as flock size increased over 11-15, their vigilance levels increased. This was possibly related to aggression avoidance when feeding on patchy, defendable food such as cow dung, or may have been related to observational learning when feeding on cryptic, non-defendable food items such as sub-soil invertebrates. As flock size increase, rates of aggressive interactions increased especially when choughs were feeding on dung and involved first year choughs to a greater extent than older birds. 14. Young choughs with their parents, while feeding on food items within dung had higher feeding rates, spent more time feeding and less time begging than when the family group was feeding on subsoil invertebrates. 15. Although sample size was small, the majority of colour-ringed female first time breeders were three, although several did breed in their second year. A higher proportion of first time breeders of four years old or over were male.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Ecology
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77982
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:45
• Last Modified: 30 Jan 2020 15:45
• URI: https://theses.gla.ac.uk/id/eprint/77982