Territoriality in the Least Flycatcher (Empidonax minimus).

Abstract

A study was conducted 23 June - 3 August, 1981 at UMBS to determine whether territory size changed through the breeding cycle. A very dense population of Least Flycatchers in the east end of the Station grounds was chosen for the study. Territory size proved to be constant through most of the breeding season and then to increase as population pressures decreased. These changes occurred irrespective of stage in breeding. Disparity in starting dates for nesting implied females were arriving over a two month period after arrival of males in May. This resulted in ummated males, and nests at all stages present together for over a month. Possibly stemming from this was a case of polygyny, apparently the first described for the genus Empidonax. Finally, further research into frequency of polygyny at this site, and determining factors which make one territory better than another would provide insight into the evolution of territoriality and what requirements determine territory size.