A COMPARATIVE-ANALYSIS OF THE DIETS OF THE CHOUGH PYRRHOCORAX-PYRRHOCORAX AND THE ALPINE CHOUGH PYRRHOCORAX-GRACULUS COEXISTING IN THE ALPS

The diets of the Chough Pyrrhocorax pyrrhocorax and the Alpine Chough Pyrrhocorax graculus coexisting in the western Italian Alps have been compared by faecal analyses. A total of 1581 fresh droppings (405 of t he Chough and 1176 of the Alpine Chough) were collected in the pasture s of the Rhemes Valley, Aosta, Italy, from June to November 1992 and a nalysed in the laboratory, and a mean volume percentage for each item was calculated. Both species were omnivorous, including animal, vegeta ble and mineral dietary fractions. There was no overlap in the vegetab le part of the diet since the Chough fed virtually exclusively on Yell ow Gagea Gagea fistulosa bulbs (dug out from the soil), which were not taken at all by the Alpine Chough. Conversely, the Alpine Chough fed on berries and hips from September to November, but these were virtual ly ignored by the Chough. Even though animal items were collected by b oth species, their preferences were different. In June, Alpine Choughs largely collected cranefly (Tipula) larvae whilst Choughs mainly fed on Lepidoptera larvae. From July onward, Alpine Choughs mainly consume d grasshoppers while Choughs also collected Tipula pupae, Lepidoptera and ny (Bibionidae) larvae and beetles (Scarabaeidae and Staphylinidae ). Interspecific morphological and behavioural differences may be part ly responsible for the segregation observed. Chemical composition and caloric contents of the food items suggest that the balance between co sts of collecting and benefits of consuming may also contribute to die t differentiation. Both species took a broad spectrum of food, and the re was no clear indication that the different population densities of the two Choughs in the Alps were directly correlated with diet, even t hough some data suggest that during autumn the Alpine Chough might hav e a diet better adapted to the high mountain environment than the Chou gh.