Regionwide polygyny in willow flycatchers

Most species of North American flycatchers (Tyranidae) are believed to be normally monogamous (Skutch 1960, Verner and Willson 1969). Some instances of bigamy are known for the Eastern Phoebe (Sayornis phoebe; Sherman 1952), Eastern Wood-Pewee (Contopus virens; W. J. Smith, cited in Eckhardt 1976), Western Wood-Pewee (C. sordidulus; Eckhardt 1976), and Acadian Flycatcher (Empidonax viriscens; Mumford 1964). Recently, local incidences of polygyny have also been reported for the Least (E. minimus; Briskie and Sealy 1987) and Willow (E. traillii; Prescott 1986) flycatchers. Here, we present details on two additional instances of polygyny in Willow Flycatchers in different regions of North America, including information on the behavior and nesting ecology of polygynous trios.