A. Rolando et P. Laiolo, A COMPARATIVE-ANALYSIS OF THE DIETS OF THE CHOUGH PYRRHOCORAX-PYRRHOCORAX AND THE ALPINE CHOUGH PYRRHOCORAX-GRACULUS COEXISTING IN THE ALPS, Ibis, 139(2), 1997, pp. 388-395
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.