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Title: Conservation and ecology of the red-billed chough Pyrrhocorax pyrrhocorax
Author: McKay, Clive R.
ISNI:       0000 0001 3624 9578
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1996
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1. The Red-billed Chough Pyrrhocorax pyrrhocorax has a population of approximately 1000 breeding pairs in the British Isles, and is afforded special protection under Annex 1 of the EC Directive on Wild Birds. Its British range has contracted over the last 200 years, and it is now restricted to the western coasts of Ireland, Wales and Scotland, and to the Islae of Man. 2. The main aims of the study were: 1) to identify the factors which currently limit the distribution of the Chough, and which may have caused its recent decline, and 2) Ao describe habitat use and habitat selection by Choughs, particularly in relation to land use practises, to identify measures which could be taken to conserve the species in Scotland and/or to re-establish it in its former range. 3. This study was carried out on the Inner Hebridean island of Islay, which held approximately 90% of the Scottish Chough population at the time of the study (c. 105 pairs). The island supports a wide range of habitats and land-uses. Particular attention was focussed on the possible threat to Choughs posed by the afforestation of part of the Rhinns of Islay in the early 1980s. 4. The Chough's decline in Scotland has been protracted, with archaeological remains from outwith the recent range suggesting that it was even more widespread prior to 1750 when literary recording began. This suggests the involvement of a long-term climatic relationship in the decline. However, the Chough's distribution since 1750 in Scotland shares the same climatic characteristics as currently occupied areas, suggesting that climate change in this period was probably not the cause of the recent range contraction. It is more likely that the recent decline was accelerated by high levels of persecution/collecting at the turn of the century, and by agricultural intensification in the 20th century. The recent historical range in Scotland was shown not to have been as extensive as suggested in the literature, and no evidence was found to confirm the suggestion that birds formerly bred far inland. 5. The Chough's distribution in Britain shows a close correlation with areas which have both extremely mild winters and warm summers. Based on these climatic characteristics, the Chough's "Potential Climatic Range" was identified. It was concluded that the Mull of Galloway (Scotland) and Cornwall (England and Wales) are currently the most climatically favourable areas for Choughs in the respective countries, despite the species' recent extinction in these areas. This paradoxical situation may be a result of the most favourable climatic conditions for Choughs also favouring detrimental agricultural intensification. 6. Nest-site availability was shown to limit abundance within the potential climatic range. Absences from Coll and Tiree are explained by lack of nest-sites, as is the small population size on Colonsay. Provision of artificial nest-sites in areas of low availability of natural nestsites which also contain suitable feeding habitats (see below) is recommended. 7. The main habitats used by feeding Choughs on Islay were grazed improved and unimproved pastures, grazed mature dune systems, grazed heath/acid grassland mosaics, rock outcrops and field boundaries. Within these habitats herbivore dung (especially cow dung) and carcases provided important supplementary feeding opportunities. There are marked seasonal changes in habitat use, suggesting that a range of habitats is required in a small area to support Choughs. An age-related difference in dung-feeding was demonstrated. Short vegetation structure and a high component of bare ground were the preferred characteristics of improved pasture fields used for feeding. These characteristics may over-ride simple prey abundance in determining feeding site preferences. This suggests that Choughs may use visual clues such as invertebrate burrow entrances to locate sub-surface prey items. 8. Permanent grazing, high grazing pressure, and a mixture of small and large grazing herbivores all contribute to the maintenance of the right habitat structure and in the provision of a range of feeding opportunities for Choughs. Large herbivores remove rank vegetation and their dung supports proportionally more dung invertebrates than that of small herbivores, whilst grazing by smaller herbivores produces the shortest swards. 9. Choughs on Islay feed primarily on inactive soil-, dung- or carcase-dwelling invertebrates, with some cereal grain taken in the late autumn/early winter. Invertebrates were dominant in the diet throughout the year. 76% (by fresh weight) of prey items taken were soft-bodied invertebrates, mostly larval forms. Faecal and pellet analysis may under-estimate the proportion of soft-bodied prey in the diet, and over-estimate the proportion of vegetable matter, particularly if samples are collected from roost sites. There is a clear need for feeding experiments with captive birds to calibrate findings from faecal analysis. 10. The relationship between climate and the Chough's range in Britain is probably brought about through the effects of climate on the productivity, growth and mortality of the invertebrate populations which make up its diet. Experimental and comparative studies showed that the fecundity, growth and survival of Tipulid larvae was greater within the Chough's range compared to areas with colder winters. 11. The Chough's specialised insectivorous diet in Britain contrasts with that of other races throughout the Eurasian range whose diet is more catholic. It is proposed that inter-specific feeding competition with other corvids, particularly the Rook Corvus frugilegus, may have been responsible for the evolution of the Chough's specialised feeding habits and small body size within Britain. 12. A range of favourable and detrimental land uses was identified. The most important land use to Choughs was considered to be the maintenance of year-round high grazing pressure by both large (e. g. cows) and small (e. g. sheep) herbivores. Research into provision of feeding sites by carcase burying and the provision of linear habitat "islands" within fields is recommended.
Supervisor: Monaghan, Pat Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QL Zoology