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.

Highlights

  • Feeding ecology of a bird of prey, like other birds, is a key for understanding their ecology and for defining conservation measures, since food is a primordial and determining factor (e.g. NEWTON, 1979; KORPIMÄKI, 1986; VILLAGE, 1990; KORPIMÄKI and NORRDAHL, 1991; VIÑUELA and VEIGA, 1992; BUTET and LEROUX, 1993; ARROYO, 1998)

  • There were no significant differences in diet composition among the three sites in the study area ( 210 = 11.937; p > 0.05), when seven large classes of prey were considered: Orthoptera, other invertebrates, reptiles, birds, eggs and mammals [K = 7])

  • We found an inverse correlation among the proportion of invertebrates and reptiles versus latitude, and a positive one between mammals and latitude (r = 0.622, p < 0.001) (Table 2), in agreement with TERRAUBE and ARROYO (2011)

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Summary

Introduction

Feeding ecology of a bird of prey, like other birds, is a key for understanding their ecology and for defining conservation measures, since food is a primordial and determining factor (e.g. NEWTON, 1979; KORPIMÄKI, 1986; VILLAGE, 1990; KORPIMÄKI and NORRDAHL, 1991; VIÑUELA and VEIGA, 1992; BUTET and LEROUX, 1993; ARROYO, 1998). Until 1992, the information on the biology of the Montagu’s Harrier (Circus pygargus) in Portugal was anecdotal, and in the context of other more general studies on birds of prey of Castro Verde region (ONOFRE, 1996), data was collected on the diet of this species (ONOFRE, 1994). In terms of food ecology, this species is one of the best studied birds of prey in Portugal and the same holds true for the Palearctic. Many studies on the food ecology of Montagu's Harrier are available, beginning with THIOLLAY (1968) in western France, and more recently by MIRSKI et al (2016) in eastern Poland. ARROYO et al (2004) and TERRAUBE and ARROYO (2011) provided an excellent picture about the diet of this species on the western Palearctic and its variation along with latitude, longitude and habitat

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