Euphagus carolinus (Rusty Blackbird) has suffered a steep population decline over the past 40 years, yet we still understand little of the basic biology of the species, particularly its social organization. During the spring of 2007, we located a loose colony of Rusty Blackbirds breeding in Piscataquis County, ME. The core colony consisted of six nests within 6.9 ha. These nests were located within a 70-ha clearcut dominated by regenerating Picea rubens (Red Spruce), P. mariana (Black Spruce), and Abies balsamea (Balsam Fir). Within 1500 m of the core colony, we located two “satellite” nests in young forests regenerating from heavy partial harvests. We observed mobbing behavior by multiple individuals from different pairs, suggesting that coloniality in this species may be an antipredator strategy.