The breeding ecology and conservation of the Ring Ouzel in Britain – PhD thesis by Ian Burfield

Summary

The ring ouzel Turdus torquatus is a summer migrant to Britain, where it is characteristically associated with upland areas. Populations have declined steadily since early in the 20th century, and the species’ range contracted by 27% between 1970 and 1990. A national survey in 1999 estimated that fewer than 7,600 pairs remain, and the species is now of high conservation concern in Britain. Limited evidence from ringing recoveries suggests that British and continental birds winter in similar areas of Spain and north-west Africa. Since most continental breeding populations appear stable, this study focussed on increasing knowledge about the species’ breeding ecology and habitat requirements in Britain, with the aim of shedding light on whether factors operating on the breeding grounds might be implicated in causing the decline.

A comparative approach was used to examine potential differences in the breeding biology and reproductive success of two contrasting populations in Scotland: one stable (Glen Esk, Tayside) and one declining (Moorfoot Hills, Borders). No significant differences were detected, with both populations experiencing high levels of nesting success and productivity. Chick growth rates were similar, and faecal analysis revealed that earthworms dominated nestling diet in both areas. It was not possible to examine whether there were any differences in annual survival, but observed return rates of marked adults and juveniles were similar.

The species’ habitat requirements were quantified to assess the impacts of land-use change and provide information for upland management. Birds in both areas preferred to site their nests in tall heather on steep slopes, particularly in stream gullies or on crags. Adults in Glen Esk selected short grass swards and intimate grass/heather mosaics when collecting food for their chicks, but avoided ungrazed areas and conifer plantations. In relation to habitat availability, the composition of home ranges in Glen Esk reflected these preferences. Most contained relatively little heather moor and larger amounts of grass moor. Home ranges also comprised a greater number and richness of habitat patches than random areas of equivalent size. In the Moorfoots, breeding sites occupied during the 1960s were more likely to have retained ouzels if there was a high proportion of grass moor within a 500 m radius.

These results suggest that increased grazing intensities in Britain over recent decades may have had complex effects on ring ouzels, the precise impacts depending on the initial balance between heather moor and grass moor. In many parts of the Moorfoots, for example, further increases in grazing pressure would threaten the few remnants of tall heather supplying nest sites. In contrast, the species’ active avoidance of conifer plantations suggests that upland afforestation has probably had negative consequences for ring ouzels. Thus, while the ultimate cause of the species’ decline remains unclear, this study has increased knowledge about one of Britain’s most poorly known birds and provided important information for ouzel conservation.

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