Seasonal variation, interspecific overlap and diet selection in three sympatric shrike species (Lanius spp.)

Full article

Published:

Volume 40(2), December 1993. Pages 143-154.

Language:

Spanish

Original title:

Variación estacional, solapamiento interespecífico y selección en la dieta de tres especies simpátricas de alcaudones (Lanius spp.)

Keywords:

diet, interspecific dietary overlap, Lanius collurio, Lanius excubitor, Lanius senator, northwest of the Iberian Peninsula, seasonal variation, trophic selection.

Abstract:

The seasonal variation in diet, interspecific dietary overlap, and trophic selection of three shrike species (Great Grey Shrike Lanius excubitor, Red-backed Shrike Lanius collurio and Woodchat Shrike Lanius senator) were studied in an area of sympatry in the northwest of the Iberian Peninsula through pellet analysis and estimates of potential prey availability. As to the number of prey, the insects constituted the bulk of food in the three species. Taking into account orders, there were significant seasonal differences in the diet in all cases. There were significant interspecific differences in diet during spring and summer due to the high percentage of vertebrates consumed by Great Grey Shrikes. The differences among species in the size of invertebrate prey were significant, the Great Grey Shrike capturing the largest prey, although there were no differences between the Red-backed and Woodchat Shrikes. In terms of energy content, the contribution of vertebrates to the nourishment of Great Grey Shrikes was higher than that of invertebrates during all seasons except autumn; in that respect, the contribution of invertebrates to the nourishment of Red-backed and Woodchat Shrikes was always higher than that of vertebrates. The three species selected Hymenoptera and Coleoptera positively and Heteroptera and Arachnida negatively. Orthoptera were very positively selected in winter by the Great Grey Shrike; nevertheless, this species consumed them in accordance with their availability during the rest of the year. Red-backed and Woodchat Shrikes showed negative selection on orthoptera.