Humans and carnivores can alter ungulate behavior through fear, which can vary with intensity of actual or perceived risk. However, our understanding of risk effects in human-carnivore-ungulate systems is limited by a lack of studies which account for risk from humans and all predator species in multi-predator systems. We investigated the diel activity of white-tailed deer in response to diel activity of wolves, American black bears, coyotes, bobcats, and humans in Michigan, USA, during July–September 2009–2019. We estimated deer mortality risk using a radio-collared sample of neonatal (n = 365) and adult (n = 391) deer, and we evaluated deer, predator, and human activity using passive (n = 250) and baited (n = 116) remote cameras.
Results/Conclusions
Neonatal deer had greater mortality risk than adults, especially from predation. All deer mortalities for which cause could be determined were attributed to predation, humans, or disease. Wolves, bears, coyotes, and bobcats accounted for all deer predation events in which the predator species could be determined. Human activity was strongly diurnal, while predators were primarily nocturnal with a high degree of overlap among species. Deer were primarily diurnal when fawns were present, and nocturnal when fawns were absent. Our results support risk-allocation behavior in diel activity among deer, wherein deer accompanied by neonates structure their diel activity to minimize encounters with predators, while adult deer without neonates do not appear to avoid predators. Our results further indicate that the large overlap in diel activity schedules of all 4 predator species resulted in a diurnal “safe period”, which neonatal deer appear to take advantage of through increased activity. A strong negative correlation between human and predator activity could indicate humans suppressed diurnal predator activity, although this relationship was only correlative in our study. We conclude that systems where multiple predators have high temporal niche overlap can create temporal refugia for prey, which may facilitate prey persistence in multi-predator systems.