Eagles are powerful raptors whose diets are primarily composed of medium-sized vertebrates captured through active hunting or acquired through scavenging. Their feeding behavior is governed by a simple energy-return equation: the caloric value of the prey must justify the energy expended to find, capture, and subdue it. The general nature of their prey makes the tiny, specialized shrew an unusual potential meal, but the answer is not a simple “no.”
The Standard Diet of Eagles
Eagles are apex predators that typically focus on prey offering a substantial caloric payout. For species like the Bald Eagle, fish are the preferred and often primary food source, with their habitats centered around large bodies of water where this prey is abundant. They are also skilled at consuming waterfowl, small mammals like rabbits and squirrels, and readily scavenge carrion, especially during winter months.
Golden Eagles often hunt in more open, mountainous terrain, and their diet centers on medium-sized mammals such as rabbits, hares, and marmots. These raptors are opportunistic, but they generally target prey that can sustain them for a period. An eagle often only needs to eat about one-half to one pound of food daily, and they can store up to two pounds of food temporarily in a crop, sustaining them for days.
Shrews: Why They Are Atypical Prey
Shrews are tiny mammals, weighing only around an ounce, making them an inefficient food source for a large raptor. Their diminutive size and high metabolic rate mean they offer a low caloric return compared to the effort an eagle would expend to hunt them. The high energy cost of capturing such a tiny animal rarely makes the endeavor worthwhile for a bird that weighs several pounds.
A more significant deterrent to predation is the shrew’s chemical defense. Shrews possess scent glands on their flanks that emit a strong, musky odor when the animal is stressed or killed. Many mammalian predators, such as foxes and raccoons, will kill a shrew but then leave the carcass uneaten due to this musky odor.
Some shrew species, such as the Northern Short-tailed Shrew, are venomous. They deliver a neurotoxic venom through grooved incisors, which is used to paralyze or kill their smaller prey. While the venom is unlikely to be lethal to a large eagle, the potential for an unpleasant or debilitating effect upon consumption adds another layer of avoidance for a discriminating predator.
Confirmed Instances of Shrew Predation
Despite these deterrents, shrews are occasionally consumed by eagles. The presence of shrews in an eagle’s diet is often linked to periods of extreme food scarcity, such as harsh winters, when preferred prey is unavailable. In these circumstances, the eagle is driven by hunger to consume whatever protein source is readily encountered, even if it is a low-quality or unpalatable meal.
Evidence of shrew consumption is sometimes discovered through the analysis of eagle pellets, which are masses of indigestible material like fur, bones, and feathers that raptors regurgitate. However, the presence of shrew remains in a pellet does not always mean the eagle hunted and ate the shrew directly. Shrews are insectivores that frequently hunt and consume rodents and other small mammals.
The shrew may have been consumed as a result of secondary predation, where the eagle eats a larger mammal or bird that had recently eaten a shrew. Eagles are known to scavenge on carrion, and if a shrew carcass is found that has not yet developed its full unpalatable musk, it may be consumed. While shrews are not a regular part of the eagle’s diet, they are occasionally eaten when the circumstances demand sustenance.