Grus americana (Whooping Crane) are particularly susceptible to colliding with power lines due to their wing loading, size, and flight behavior, often resulting in fatal collisions. This is the first study assessing the specific biological (sex, age, flock size), environmental (time of year, time of day), and structural (line type, line direction) circumstances associated with Whooping Crane collisions with power lines in all 4 reintroduced populations. We documented 65 instances of mortality from power lines and found that both migratory and nonmigratory reintroduced populations were at risk. In migratory populations, collisions seemed more likely to occur during migration. Significantly more males collided with power lines than females in nonmigratory populations. Both transmission and distribution lines posed threats for collisions in all populations. We documented more collisions of juvenile and sub-adult cranes than adults. This study aims to provide insight into the circumstances in which power lines pose a threat to cranes, which will inform efforts to mark power lines and guide decisions on release locations for captive-reared cranes, in hopes of ultimately reducing mortalities and improving population growth for reintroduced Whooping Cranes.