Collectively, the Bald Eagle is an opportunistic feeder with a large number of prey items recorded. Over 250 species of fish, birds, mammals, reptiles, amphibians, and invertebrates are known to have been consumed by eagles continent-wide. Clearly, the diet varies geographically and particularly seasonally as these birds adjust their feeding behavior to take advantage of the most readily-available food source. Live prey is taken frequently but some consider the Bald Eagle to mainly be a carrion eater given that its food is often dead or dying from other causes before being eaten. Small amounts of vegetable matter are also eaten, whether intentionally or incidentally while consuming animal prey.
Overwhelmingly, fish is the single most important food type but birds and mammals are also heavily consumed. Conclusions from studies of diet seem variable. Some studies suggest that coastal eagles eat more birds and less fish and mammals than inland eagles that ate more fish and mammals and less birds. Other studies showed coastal birds eating more fish and birds whereas eagles from dry, interior ecosystems were almost entirely mammal eaters. Despite the inevitable variations, reptiles, amphibians and all other species are a small percentage of the diet compared with fish, birds and mammals. These latter three groups represent more than 90 percent of the Bald Eagle diet across North America.
One summary of diet studies showed the following percentages of foods:
Food type Prey items Biomass
Fish 32% 33%
Birds 43% 35%
Mammals 19% 32%
All others 6% .1%
Another summary showed the results of various studies on a geographic basis:
Coastal Group Coastal Group Eastern Kansas
FOOD Number 1 Number 2 States
Fish 65% 19% 52% 0
Birds 19% 59% 33% 1%
Mammals 1% 5% 5% 99%
In Cape Breton Island, Nova Scotia, fish were 66 percent of all prey items and were found in 92 percent of all samples of eagle diets that were studied. Cod totaled 71 percent of the fish component.
The total list of fish species consumed is long and does not only reflect fish that are easy to catch live because they primarily live near the surface. Some deep dwellers come near the surface to spawn or their carcasses become accessible after the breeding season. Some examples of known prey include all pink, chum, coho, chinook and sockeye salmon, kokanee, rainbow trout, herring, eulachon, Pacific sandlance, various flounders, sculpins, various rockfish including red snapper, dogfish, various species of catfish, suckers, carp, perch, pollock, striped bass, mackerel, gizzard shad, sheepshead, blue pike, northern pike, pickerel, sunfish, mullet, shiners, eel and char. Entrails or unwanted species from fishing operations are often taken in inshore waters.
The total list of birds eaten throughout North America contains the most number of species of the 3 main food groups. Many are taken as live prey but carrion or hunter-wounded species are also eaten. The following list gives some sense of the size and variety taken: loons (2), grebes (5), Northern Fulmar, shearwaters, petrels (2+), Brown Pelican, cormorants, Great Blue Heron, Cattle Egret, herons (6), Canada Goose, Emperor Goose, ducks (20 +), ptarmigans, domestic chickens, Black Oystercatcher, Wild Turkey, Sora, American Coot, gulls (7+), tern (2+), murres, auklets, puffins, murrelets, Northern Flicker, Common Raven, sparrows (3), Lapland Longspur, and Rosy Finch.
As with fish and birds, mammal prey is taken live or eaten as carrion. Live prey tends to be the smaller species such as rodents or ground squirrels with larger animals eaten as carrion. Examples of food items include introduced and native hares and rabbits, various ground squirrels, fox pups, Norway rats, sea otter pups, young pigs, muskrats, opossum, skunk, voles, weasel, marten and as carrion, white-tailed and mule deer, elk, whales, sea lions, domestic sheep and cattle and miscellaneous road killed animals. The afterbirth of domestic livestock is eagerly eaten but documented examples of calves or lambs being killed are few. Other scavengers such as ravens and magpies or coyotes cause injury or death to domestic animals before the Bald Eagle takes advantage of the carcass.
The list of reptile and amphibian species taken is short but includes frogs, black rat snake, racers, and musk turtle.
There are at least 20 species of invertebrates eaten and many are marine organisms including squid, octopus, abalone, crabs, mussels and amphipods.
Much misinformation surrounds the maximum size of prey that an eagle will attack or can carry away. In all likelihood, based upon experiments to test weighted flight capacity, prey items weigh no more than five pounds (2.3 kilograms) and usually much less. It is unlikely that an eagle could fly very far with items weighing five or six pounds (2.3 to 2.7 kilograms). A bald Eagle can drag objects in water weighing over 10 pounds (22 kilograms) for very short distances (25 feet [8 meters] or less).
PELLETS
Bald Eagle pellets are quite large, averaging 4 inches (10.2 centimeters) long and 1.5 inches (3.8 centimeters) wide. While mammal and bird remains are well-represented, fish may be under-represented in pellets due to the relative ease with which they are digested, especially smaller ones.
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