The stoat (Mustela erminea) is a small, fierce predator distributed across the circumpolar regions of the Northern Hemisphere. This member of the weasel family is recognizable by its long, slender body, short legs, and a distinctive black tip on its tail. In its white winter coat, it is often called the ermine. The stoat is an obligate carnivore, requiring a diet consisting almost exclusively of animal protein. This biological necessity dictates its lifestyle as a relentless, opportunistic hunter, constantly pursuing its next meal to fuel its high-energy existence.
A Carnivorous Diet: Primary Prey and Opportunistic Meals
The foundation of the stoat’s diet is small mammals, primarily rodents such as voles, mice, and shrews. The stoat is equipped to pursue these animals into their underground burrows. A significant portion of its intake also comes from lagomorphs like rabbits and hares. Although capable of killing adult prey much larger than itself, the stoat often targets the young, such as rabbit kits, which are a valuable, high-calorie food source.
The stoat is highly opportunistic, consuming a wide variety of secondary food items when preferred prey is scarce. These include birds and their eggs, especially those of ground-nesting species, which the stoat can raid by climbing trees. The diet also incorporates amphibians, reptiles, fish, and invertebrates, such as insects. In certain environments, like the alpine regions of New Zealand, invertebrates can account for 30–50% of food items. When animal prey is unavailable, the stoat may consume carrion or resort to emergency foods like fruits and berries, though these plant-based items do not provide necessary long-term nutrients.
The Stoat’s Hunting Prowess
The stoat’s hunting success results from its specialized physique, allowing it to move with exceptional speed and agility. Its elongated body enables it to follow rodents and lagomorphs deep into narrow, subterranean tunnel systems. Stoats possess excellent senses of smell and hearing, which they use to track prey relentlessly. Once a stoat catches its prey, it delivers a precise nuchal bite to the base of the skull, causing immediate immobilization.
The capture of larger prey, such as a rabbit, sometimes involves a behavior described as the “weasel war dance.” During this erratic display, the stoat performs tumbling movements that confuse or distract the victim, allowing the predator to close the distance for the final attack. Due to intense metabolic demands, the stoat often engages in “surplus killing” when prey is plentiful. This excess food is then strategically stored, or cached, in its den for later consumption, providing insurance against future scarcity.
Why Stoats Must Eat Constantly: High Metabolism
The stoat’s relentless hunting behavior is driven by a high metabolic rate necessitated by its unique body structure. The animal’s long, thin body results in a high surface area-to-volume ratio, which is inefficient for retaining body heat. This shape causes rapid thermal loss to the environment, forcing the stoat’s metabolism to run continuously at a high rate to maintain a stable internal body temperature. Without a sufficient and constant energy supply, the stoat would quickly succumb to hypothermia.
To counteract this constant energy drain, a stoat must consume a significant amount of food every day, typically needing to eat about a quarter of its own body weight to sustain itself. Stoats have a short digestive tract and very little capacity for fat storage. This means they cannot gorge on a large kill and rely on those reserves for an extended period. The lack of significant fat reserves means they must hunt and feed almost daily, making the search for prey a continuous activity.