Eastern gray squirrels and fox squirrels are common across North America, but their lives in the wild are typically brief. While some individuals survive up to 12 years, the average lifespan is often only 18 months to two years, demonstrating a high mortality rate. This short existence results from a combination of natural forces and increasing human-related hazards. Factors range from the ancient threat of predators to the modern dangers of toxic chemicals and infrastructure.
Predation and Natural Mortality Factors
Mortality from natural enemies and the harsh environment is significant, especially in rural areas. Raptors, such as red-tailed hawks and great horned owls, present a constant threat from the skies, snatching squirrels from tree branches. Young or inexperienced squirrels are especially vulnerable to these aerial hunters.
On the ground, coyotes, foxes, and snakes actively hunt squirrels, often targeting those distracted while foraging. Domestic and feral cats are also major contributors to squirrel deaths in suburban settings. Beyond direct predation, environmental pressures take a heavy toll. Starvation during harsh winter months or resource scarcity is a major factor, as are severe weather events and the flooding of nests.
Disease and Pathogens
Infectious agents and parasites frequently weaken squirrels, making them easier targets for predators or unable to forage effectively. The Squirrel Poxvirus is a notable threat. While carried by North American gray squirrels without harm, the virus is often fatal to red squirrels, causing severe lesions that impair vision and feeding.
Other health issues contribute to mortality, especially when the animal is stressed. Heavy infestations of external parasites, such as mange mites, can lead to severe hair loss and subsequent hypothermia during colder weather. Rabies is extremely rare in squirrels; debilitating sickness leading to death is more often caused by fungal infections.
Hazards in the Built Environment
In urban and suburban landscapes, the greatest source of squirrel death shifts from natural causes to accidental encounters with human infrastructure. Vehicular trauma is the single largest cause of mortality in populated areas, with studies indicating that over 60% of urban squirrel deaths are attributed to automobiles. This high rate results from the animal’s erratic “darting” behavior and inability to judge the speed of approaching vehicles.
Electrocution is another frequent hazard, occurring when squirrels interact with power transformers and electrical lines. The prevalence of power infrastructure means these incidents are common, often resulting in instant death. Accidental confinement also kills many squirrels, such as falling into open water barrels, swimming pools, or becoming trapped in uncapped chimneys and ventilation shafts where they succumb to exhaustion or drowning.
Toxic Substances and Intentional Controls
Chemical exposure, whether intentional or accidental, represents a modern threat to squirrel populations. The most common toxic substance squirrels encounter is rodenticide, often placed to control rats and mice. These baits are appealing and can be directly ingested, resulting in poisoning.
The most widely used products are anticoagulant rodenticides, which prevent the blood from clotting, leading to fatal internal hemorrhaging. Because this mechanism is slow, the poisoned squirrel may wander off to die in a hidden location. Secondary poisoning is also a risk: if a predator or scavenger consumes a squirrel that has ingested a lethal dose of rodenticide, that secondary consumer can also suffer from poisoning, passing the toxin through the food web. Other accidental ingestions include antifreeze, or various pesticides and chemicals stored improperly in garages or sheds.