BIGYNY OF YELLOW-HEADED WAGTAIL <i>MOTACILLA CITREOLA</i> PALLAS 1776 (PASSERIFORMES, <i>MOTACILLIDAE</i>, <i>MOTACILLINAE</i>) UNDER SYMPATRIC CONDITIONS
We present the data on bigyny of yellow-headed wagtail Motacilla citreola Pallas, 1776 (Passeriformes, Motacillidae, Motacillinae) in the Middle Volga Region (the Penza Region) as a factor of isolation under sympatric conditions.