Feeding behavior of nesting Choughs in the Scottish hebrides

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Authors: Bignal, E.M., McCracken, D.I., Stillman, R.A. and Ovenden, G.N.

Journal: Journal of Field Ornithology

Volume: 67

Issue: 1

Pages: 25-43

ISSN: 0273-8570

Three pairs of individually color-banded Choughs (Pyrrhocorax pyrrhocorax) were studied on the island of Islay during the 1992 incubation and nestling periods (21 April-16 June), to investigate the effects of land management factors on adult feeding behavior. The behavior of individual birds was recorded at 1-min intervals. The land utilized by the birds was mapped by farm management unit (compartment) and the use of these, and of 10 biotopes, were recorded together with nine behavioral activities. A total of 15,128 1-min observations was collected on these birds. All three pairs showed distinct selection for grass pasture (either old or new grassland). Over 90% of each pair's time was spent in food collection activity, and invertebrate sampling suggested that the birds were feeding mainly on soil-dwelling tipulid fly larvae (Diptera: Tipulidae). Analyses of compartment agricultural management characteristics data indicated that the small number of preferentially used compartments were those in which (1) management during June-September 1991 produced medium-high grass sward heights, and (2) management between January and May 1992 produced short, open swards. It is suggested that this combination of seasonal management encouraged high numbers of tipulid larvae in the soil during winter and spring and provided optimum foraging conditions for the birds both before and during the incubation and nestling periods. The implications of the findings for pasture management are discussed in relation to their potential to provide relatively simple agricultural management prescriptions to favor Choughs on Islay during the incubation and nestling periods.

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