Первый случай гнездования малого волчка Ixobrychus minutus и гибридов I. minutus с I. sinensis на Дальнем Востоке России

Abstract

In 2007 in the suburbs of Vladivostok we discovered the first nesting settlement of the Chinese bittern Ixobrychus sinensis in the Russian Far East and documented the first reliable case of breeding of the little bittern I. minutus at a distance of about 3,000 km from the boundaries of its main range. In the subsequent years, 2008–2010, one pair of bitterns nested every year in the study area. The colour of the body and the shape of the beak of both partners were largely typical of the little bittern, but there were signs characteristic of the Chinese bittern, which made it possible to identify them as hybrid individuals. For the first time evidence of hybridisation was obtained for species of the genus Ixobrychus. Six nests, 37 eggs and 26 chicks of Chinese bitterns and hybrids were described. Based on the collection material (95 carcasses) and the data of hidden video filming (112 hours), the species and species-specific morphometric parameters of bitterns were determined. In a comparative perspective the morphology and colouration, nesting biology, behaviour of adults and juveniles, and the daily rhythm of heating and feeding nestlings were described in detail. Despite the allopatric distribution (with joint wintering grounds in India) and a clear morphological gap, habitats, phenology and biology of reproduction, behaviour and feeding as well as most types of calls of these species appeared to be largely similar. In the case of dispersal of the little bittern to the east, the above factors can contribute to hybridisation.