Annual Cycles of Wagtails (Passeriformes, Motacillidae) in Northwestern Siberia: Comparative Aspects

Аннотация

Abstract—The annual cycles of pipits and wagtails, which were studied during field and experimental observations in the Lower Ob River basin and Yamal Peninsula, have many common features. All species are similar in dates of arrival, nesting, molting, and departure onset; however, the timing of postnuptial migration and prenuptial molting differ somewhat. Positive air temperatures are an environmental factor that determines the beginning of arrival to the forest tundra and tundras. Only yellow wagtails arrive with developed gonads, while the other species require additional stimulation by a photoperiod of 24L : 0D. The reduction of some nesting stages is presumably an attempt of boreal populations to increase reproductive success. Differences in the annual cycle program are observed during the postnesting period. These variations include the timing of the onset and duration of postjuvenile and postnuptial molting, as well as the degree of overlap of postnuptial molting with nesting, the degree of overlap of the migration state with molting, photoperiodic molting conditions, and autumn migration. The intraspecific rhythm of migration in combination with environmental conditions along the migration track determines the timing of arrival to wintering sites. The threshold values of photoperiodic intervals of wintering and prenuptial molting in different species correspond to the latitude of hibernation and, possibly, determine this latitude.