Diet of a Southweatern Most Population of Montagu’s Harrier (Ciercus pygargus) in the Palearctic

Abstract

Data on Montagu’s Harrier biology was gathered in 1992 during a broader survey on birds of prey in the region of Castro Verde, during which pellets and prey remains were harvested in order to study their diet. Main land-use of the study area was extensive cereal crops with fallow fields. A total of 143 pellets collected in perches were analyzed and 1351 items were counted. Invertebrates were the main prey in number (97.2%) and biomass (32.9%). Birds and mammals were also important prey in terms of biomass (30.2 and 28%, respectively), despite its low numbers in relation to all identified prey (4.3 and 1.3%, respectively). Prey weighing less than 30 g were the most frequent (98.1%) with a corresponding biomass of around 62.1%. For prey weighing more than 100 g only Lagomorphs contributed to it, totaling 25% in terms of biomass, despite their remarkably low numbers (0.4% of total prey). This high predation on invertebrates while low on mammals agrees, with the known latitudinal trends of diet composition of the Montagu’s Harrier, and some other birds of prey, along the Palearctic. In this part of Iberia, where large orthopterans are particularly common in extensive cereal fields, strong presence of insects was found in the diet of Montagu’s Harrier populations. This feature seems to be related to the abundance of orthopterans in southern Europe.