Ecology and behaviour of winter floaters in a subalpine population of Willow Tits, Poecile montanus

Abstract

Willow Tits Poecile montanus maintain yearlong territories defended by a male and femalemated pair. Outside the breeding season the adult pair lives togetherwith two to four unrelated first-year Willow Tits that have settled after a post-natal dispersal. Because the habitat of the species is largely saturated with dominant territory owners and the flock size is limited, many juveniles fail to become resident flock members. These non-territorial birds behave as migrants during autumn or stay in the area for a short time (transients) or live as floaters that switch among flocks or roam about singly. The floaters (51 colourringed) and transients (450 colour-ringed) did not differ physically or in their foraging behaviour, whereas birds of these groups weremore vigilant and used less time for foraging than residents (114 colour-ringed). Floaterswere sociallydominated by residents and also maintained a poorer nutritional status. The mean wing length of males observed for the last time in November was significantly longer than that of those seen for the last time in September or October, whereas no such differences were found for body mass or nutritional status. The floatersmoved around solitarily and crossed several Willow Tit territories (males 2-8 territories, females 2-5 territories; mean territory size ca 25 ha). Only three male floaters settled, one disappeared in December the same year, one was seen for the last time in March and one in April the following year.