18The red-winged blackbird (Agelaius phoeniceus) is one of the most abundant bird species in North America, with an estimated spring breeding population of 150 million individuals that nest in emergent wetland vegetation and upland habitats throughout the continent (Yasukawa and Searcy 1995; Forcey et al. 2015; Rosenberg et al. 2016). During the nonbreeding season, red-winged blackbirds are often found in flocks numbering from a few birds to many thousands, sometimes in association with other blackbird species and European starlings (Sturnus vulgaris). In winter, red-winged blackbirds and these associated species gather in roosts occasionally numbering over 10 million birds (Meanley and Royal 1976; White et al. 1985).