Parameters of the autumn migration stopover of the chiffchaff (Phylloscopus collybita Vieillot, 1817) (Sylviidae, Aves) in the conditions of the middle taiga in the Eastern Russian plain

Parameters of the autumn migration stopover of the chiffchaff Phylloscopus collybita (Vieillot, 1817) in the taiga zone of the Eastern Russian plain were estimated. The studies were carried out in 2015–2019, a total of 1,634 birds were included in our analysis. It has been established that migrating chiffchaffs can be conditionally divided into two groups. The first group consists of transit individuals leaving their stopover just on the day of arrival, without delay. The other group includes individuals who make stopovers for a longer period (4.87 days on average). For the birds of both groups, changes in their body weight and fat accumulation rate were revealed during one day and throughout the entire migration stopover. During an average migration stopover, birds retain their energy reserves at a certain level. In general, they accumulate no more than 5% of the average body weight in the population during the average stop period. A smaller proportion of migrants make multi-day stops when the fat accumulation rate is low. Every day of staying at a migration stopover leads to temporary surges and losses in body weight, with no increase in body fat. Birds, at the end of their migration season, spend more time and energy for looking for food. The part of migratory birds deciding to stop finds themselves in the most optimal conditions. This small group is the main reserve for preserving the population during the difficult period of migration.