Breeding ecology of Twite Carduelis flavirostris in a crofting landscape

摘要

Capsule Twite nested close to and exploited rich seed sources on machair, and had high breeding productivity relative to other studies of Carduelis finches.Aims To test whether Twite nesting distribution, breeding phenology and success, foraging habitat selection, and nestling diet in a high density population on the Western Isles of Scotland are associated with the habitats and food sources provided by agricultural management of machair habitats.Methods Breeding season transect surveys and intensive nest finding were used to quantify the habitat associations, distribution, phenology, nest success and nestling diet of breeding Twite on study areas in the Western Isles of Scotland. Individual colour-ringing was used to estimate the number of breeding attempts being made by individual adults.Results Nesting Twite were strongly associated with moorland edge habitats adjacent to machair, with most nests in Heather or shelter-belt conifers, and the birds fed almost exclusively on seed sources characteristic of machair grassland and fallows rather than moorland. Nesting success did not vary between habitats or study areas, although both clutch and brood sizes showed a mid-season peak. Individual adults made up to three nesting attempts in one season, and overall breeding productivity was high relative to other recent studies of Carduelis finches, including studies of the declining Twite population in the English Pennines.Conclusion The maintenance of rich seed sources provided by the mix of low-intensity arable and grassland management of the machair are likely to be essential to maintaining high Twite population density and indicate that management intervention to restore such seed sources in the habitats of declining populations should be a high priority.