Study

Breeding biology of Montagu's harrier Circus pygargus L. in agricultural environments of southwest Spain; comparison with other populations in the western Palearctic

  • Published source details Corbacho C., Sanchez J.M. & Sanchez A. (1997) Breeding biology of Montagu's harrier Circus pygargus L. in agricultural environments of southwest Spain; comparison with other populations in the western Palearctic. Bird Study, 44, 166-175.

Summary

The Montagu's harrier Circus pygargus is a ground-nesting raptor, which nests in agricultural habitats in parts of its range. This study investigated the impact of active nest management at harvest time on the breeding success of Montagu's harriers nesting in 'pseudo-colonies' in wheat, oats and barley fields in the agricultural landscape of northern Badajoz and southern Cáceres provinces, Extremadura, south-western Spain.

During 1987-1991, 108 harrier nests at five breeding sites were studied: 26 in 1987, 12 in 1988, 18 in 1989, 39 in 1990 and 13 in 1991. Each season, some nests were manipulated in an attempt to reduce losses resulting from farming activities; others were left unmanaged, as controls. There were no differences in laying date or clutch sizes between managed and unmanaged nests. Management involved the removal of chicks (or eggs) from nests prior to harvest and baling, and their replacement in the nest site once the whole field had been harvested.

Colonies were visited once a week from the first stages of breeding, increasing to once every three to four days during the nestling period, to collect measures of breeding success.

Although the average hatching success of managed (78%; n = 65) and unmanaged (61%; n = 27) nests were not significantly different, the principal causes of hatching failure were destruction by agricultural machinery (44%) and desertion by the female following harvesting (25%). Nest manipulation did, however, have a significant impact on chick mortality, which was on average 28% in managed nests (n = 55), compared with 67% in unmanaged nests (n = 18). Agricultural machinery (mainly mechanised harvesting) was responsible for over 50% of chick mortality in unmanaged nests, compared with only 10% of deaths in managed nests (where the main cause of chick mortality was predation). Although the average number of fledglings per successful nest was similar for managed (2.73 ± 1.16; n = 51) and unmanaged (2.60 ± 0.84; n = 10) nests, the overall breeding success of managed nests (2.04 ± 1.53 fledglings per pair; n = 68) was on average nearly three times higher than that of unmanaged nests (0.77 ± 1.28 fledglings per pair; n = 34).


Note: If using or referring to this published study, please read and quote the original paper, the abstract of which can be viewed at: www.springerlink.com/content/655m5g036x212213/fulltext.pdf

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