Gamova T. V., Surmach S. G.
Amurian zoological journal 2021; 13(4): 557-580
Field work was carried out in 2004-2006, in the northern (between the Gulf of Tartary coast, Siziman village and Samarga river) and central (Spassky district, Gayvoron village) parts of the black-browed warbler range. New insights into the species’ reproductive biology, moulting and behaviour were obtained. Geographic differences in the timing of reproduction, choices of nesting biotopes, shapes, sizes and composition of nests, sizes of clutches and growth rates of nestlings were identified. Causes of reproductive losses and factors influencing such causes have been determined. The molt of adult and juvenile birds has been described. In an area along the line stretching for more than one thousand km from the village Siziman in the Khabarovsk region in the north to the settlement of Khasan in the Primorsky region in the south, the black-browed warbler is characterized by a high degree of eurytopicity. In the north of Primorye and in the Khabarovsk region, it breeds mainly in spirea-forb thickets, arranging nests at an average height of 60 cm, while in central and southern Primorye, where the predominant nest support plants are wormwood and reed grass, the average height of nests from the ground does not exceed 40 cm. Since birds from the northern parts of the range (Northern Primorye, Khabarovsk region and Sakhalin) arrive at nesting sites 10-20 days later, they exhibit a shortened nesting cycle, when all stages of breeding and nestling development take place in a shorter time. In Sakhalin, the incubation period is reduced compared with the Primorye, taking 12 days on average instead of 15 in Primorye, with a higher growth rate of nestlings. Breeding success did not differ geographically, biotopically or depending on the timing of breeding. However, in Primorye, a positive correlation between breeding success, the average height of the herbage at the nest site and the height of the nest from the ground was found (R = 0,22-0,32, P < 0,01). Nevertheless, the density of herbage and the distance to neighbouring nests, as well as the average thickness of supporting plants, did not play a decisive role.
