[Advantages and limitations of interspecies associations in northern migratory sandpipers (Charadrii, Aves)].

Investigations were carried out at two stations of Ornithological Unit, IBPN FEB RAS, located in Nizhnekolymsk District, Yakutia, starting from May 15-20 in 1984, 1985, 1987, 1988, and 1990; at the northern coast of Pukhovoy Bay, Southern Island of Novaya Zemlya starting from June 1 in 1994; at Cape Beliy Nos, the Yugorsky Peninsula, starting from June 1 in 1995-1997. Classic associations are detected in interspecies flocks of sandpipers between the following species: the Pacific golden plover and the curlew sandpiper, the pectoral sandpiper and the long-billed dowitcher, the pectoral sandpiper and the dunlin, the grey plover and the dunlin. However, total amount of birds that form associations is not large. In species of group "A" (the grey plover, the Pacific golden plover, the pectoral sandpiper), no difference has been observed in migratory birds behavior within inter- or conspecific flocks. Species of group "B" (the dunlin, the curlew sandpiper, the long-billed dowitcher), on the contrary, change their behavior sharply depending on whether they belong to an association or not. Species of group "A" do not get any advantages when forming an association. Unlike them, species of group "B" profit from associating: a part of time spent in foraging substantially increases; more time is spent on rest and less time is spent on reconnaissance and vigilance (readiness for actions); safety of birds is enhanced. On the other hand, in species of group "B" there are also disadvantages related with associating: i.e., interspecies competition for food; foraging in suboptimal habitats which, in turn, may lead to notable increase of time spent by birds in foraging. An assumption is put forward that in species of group "B" advantages and limitations of associating cancel each other to a certain extent, and this explains rather small number of birds forming associations.