Comparative breeding ecology and hybridization of Eastern and Western Marsh Harriers Circus spilonotus and C. aeruginosusin the Baikal region of Eastern Siberia

Abstract

New information on the breeding ecology and inter‐breeding of Western Circus aeruginosus and Eastern C. spilonotus Marsh Harriers in the Baikal region of Eastern Siberia is presented. Hybridization is relatively common (one of the parents was not ‘pure’ C. spilonotus in six out of 28 nesting cases) in the Irkutsk area, where nests of a mixed pair were found with chicks in 1999 and 2000. Eastern Marsh Harriers are more similar to Western in size, biology and coloration of young birds, but to the Australasian C. approximans in their displays and mating system, and intermediate between C. aeruginosus and C. approximans in the plumage coloration of females. The systematic status (species' or ‘subspecies’) of the Western and Eastern Marsh Harriers depends on the systematic approach taken, and existing data seem to be inadequate to resolve this. The Siberian Mongolian zone of contact of these marsh harriers is unique as other marsh harriers of the world are allopatric. More research on ecology, behaviour and molecular systematics is necessary to resolve the situation.