On home-range gap-crossing

Gap-crossing may be defined as any movement by animals across swaths of inh ospitable habitat. Such behavior is the least understood of the factors tha t control metapopulation dynamics. We differentiate among active and passiv e dispersal gap-crossing and active and passive home-range gap-crossing. Fr om observations of active home-range gap-crossing by permanent-resident bir ds wintering in 47 woodlots in an agricultural landscape, we conclude that larger birds were more likely than smaller ones to cross gaps, and to cross wide gaps, and that proximity and prevalence of woodlands in the surroundi ng landscape were consistently positively related to the proportion of spec ies that crossed gaps. We discuss these results in relation to the migratio n equation of Baker and the marginal value theorem of Charnov. Knowledge of decision rules relating active home-range gap-crossing to resource levels within individual habitat fragments and risk of movement among fragments ap pears to be important for valid calculations of local population densities and metapopulation persistence.