Compensatory human and predator risk trade-offs in neonatal white-tailed deer

Abstract

Neonatal mortality is a primary determinant of ungulate population dynamics and occurs from multiple proximal causes, but few studies have compared relationships between risk factors and cause-specific mortality. We evaluated how landscape and physiological characteristics influenced white-tailed deer ( Odocoileus virginianus ) fawn risk from predators (American black bears [ Ursus americanus ], bobcats [ Lynx rufus ], coyotes [ Canis latrans ], and wolves [ Canis lupus ]), anthropogenic causes, and non-predation natural causes (i.e ., disease, injury, or starvation). We monitored 363 fawns and identified 166 mortalities in the Upper Peninsula of Michigan, USA during 2009–2019. Human development reduced fawn predation, particularly from coyotes, but predation was compensated by vehicle collisions. Coyote predation also was reduced in more forested areas, which was offset by increased predation from black bears, bobcats, and wolves. Smaller birth mass increased risk of non-predation natural mortality but did not influence predation or anthropogenic mortality. Our results suggest that for prey living alongside human development, the survival advantage of a “human shield” from predation can be offset by anthropogenic mortality. Birth mass relationships with mortality contradicted the hypothesis that predators select weaker individuals. We conclude that landscape attributes and fawn characteristics may interact with top-down, bottom-up, and anthropogenic processes to shape neonatal white-tailed deer mortality. Because some causes of mortality have opposing relationships with risk factors, combined mortality risk assessment may mask the processes driving specific mortality causes.