What Eagles Eat When Fish Are Unavailable: The Backup Diet System

Ask most people what bald eagles eat and you’ll hear one word: fish. That answer is true but incomplete — during the long stretches when fish are locked under ice, dispersed, or absent, bald eagles reveal what makes them one of the most successful raptors in North America. They are opportunists of the first order.

The fallback hierarchy: how a bald eagle decides what to eat

Raptors are energy accountants: every prey choice trades calories gained against effort and risk. Live fish in shallow, accessible water are the best deal on the menu — which is why fish dominate wherever they are easy to catch. When fish become scarce or costly to pursue, eagles step down a predictable hierarchy of alternatives rather than starve.

Field studies of bald eagle food habits show the same pattern: fish lead the prey list, followed by birds (especially waterfowl), mammals, and other material, with proportions shifting seasonally and geographically. Our complete guide to the bald eagle diet covers the full prey spectrum; the sections below focus on what happens when the top choice disappears.

Waterfowl: the first line of backup

When fish are unavailable, the most important live-prey substitute is birds — above all coots and ducks. American coots are a classic example: abundant on open water, slow on takeoff, and traveling in flocks that concentrate attention. Wintering eagles in many regions take significant numbers of coots, often by flying low over flocks and picking off repeatedly disturbed individuals.

Ducks, geese, and grebes round out the avian menu. Eagles target the weakened and the young — birds at the edge of a flock, or individuals exhausted by harsh weather. On ice-covered lakes, open water becomes a natural trap concentrating waterfowl and the eagles that hunt them. This prey-switching ability is one of the themes in our seasonal guide to what eagles eat throughout the year.

Carrion: the winter workhorse

Scavenging is the least glamorous and most important part of the backup system. In cold months, carrion — dead and dying fish along shores, winter-killed waterfowl, deer gut piles, roadkill — can supply a large fraction of daily calories. Gut piles from deer season are a reliable, energy-dense bonanza in northern states, and eagles learn the calendar.

Dead fish may be the single most underrated resource. Salmon carcasses in the Pacific Northwest, spawning-run fish in the Great Lakes, and winterkill fish along frozen shorelines all draw eagle concentrations that would otherwise have to work harder for live prey. This scavenging side surprises people who picture eagles only as hunters; our comparison of vultures and eagles explains where eagles sit on the hunter–scavenger spectrum.

Why scavenging works so well in winter

Cold weather is a scavenger’s ally. Fish die-offs, weather-stressed birds, and vehicle collisions become more frequent, and frozen ground preserves carcasses — while live prey such as fish become harder to catch. The math favors carrion precisely when hunting is hardest, one reason winter eagle counts spike along roads, rivers below dams, and areas with late hunting seasons.

Kleptoparasitism: stealing as a strategy

Food piracy — kleptoparasitism — is one of the best-documented behaviors in bald eagle ecology. The classic victim is the osprey, which hunts fish over open water and is physically outmatched by an adult bald eagle. An eagle will pursue an osprey carrying a fish, force it to drop its catch, and often snatch the fish in mid-air; observers at osprey colonies record a notable share of catches lost to piracy in some areas.

Eagles also rob each other. At salmon streams and winter concentration areas, a dominant adult frequently displaces a rival from a carcass, and juveniles — less skilled hunters anyway — rely heavily on piracy and scavenging. Stealing is not incompetence but a rational shortcut: it is cheaper to take a caught fish than to catch one. More on how these behaviors fit the broader food web is in our guide to eagle hunting behavior and the food chain.

Small mammals and colonial waterbird chicks

Rabbits, hares, muskrats, and other small-to-medium mammals form another fallback tier. Muskrats are taken around marshes and rivers, and rabbits are pursued on land, usually by eagles that have learned to hunt away from water. These prey items rarely dominate the diet but provide dependable protein in lean periods, particularly for inland-wintering eagles.

Colonial waterbirds — gulls, terns, cormorants, and herons — offer a seasonal option: their chicks. Eagle predation at heronries and gull colonies is well documented, and in some coastal and island nesting areas, young waterbirds become a significant food source during the eagle’s own breeding season — the same eagle that eats spawning fish in April may raid a gull colony in June.

Garbage and dump feeding: the last resort that built populations

At the bottom of the hierarchy sits human refuse. Historically, open garbage dumps were major winter feeding stations for bald eagles in Alaska and elsewhere, and dumps still attract eagles where landfills remain open. Gatherings there can number in the dozens or hundreds, with birds feeding on fish waste, butcher scraps, and table refuse.

Dump feeding is less common today — modern landfills are covered, and many states closed them to large birds — but the historical record is instructive. Refuse subsidy helped sustain eagle populations through hard winters, illustrating the same principle as everything else on this list: a bald eagle will exploit almost any predictable, energy-rich food source. This adaptability is a big part of why the species rebounded so quickly once DDT was banned; the recovery story and general biology are in our ultimate guide to eagles.

How flexibility explains range expansion

Bald eagles now nest farther south, farther north, and in more human-dominated landscapes than at any point in the past century, and diet flexibility is a core reason. An eagle that must have live fish needs clean, open, fish-rich water. An eagle that will also eat waterfowl, carrion, stolen fish, and refuse can live on reservoirs, rivers, farm country, and city waterways alike.

Consider the winter dynamics: eagles follow open water and food availability rather than a fixed habitat template. Reservoirs with tailwater fish, waterfowl refuges with wounded and migrating birds, and livestock country with carcasses all host wintering eagles that could not persist on a fish-only diet. Generalist feeding turns habitat from a constraint into an option.

Winter concentrations below dams

Nowhere is the backup diet system more visible than below hydroelectric dams in winter. Turbines keep water open and churn up stunned or disoriented fish — an easy meal requiring no hunting skill. Add abundant waterfowl on the open water and, on some rivers, spawning runs, and a tailrace becomes a complete winter cafeteria.

Famous examples include the Mississippi River lock-and-dam systems, where hundreds of bald eagles gather each January, and dam sites across the interior Northwest; travelers can find accessible sites in our guide to where to see eagles. The drama at these sites condenses the entire fallback hierarchy: fishing first, piracy second, waterfowl third, with scavenging eagles loafing on the ice between meals.

The golden eagle comparison: a different backup philosophy

Set the bald eagle beside its golden cousin and the contrast is striking. Golden eagles are, at heart, hunters of medium-sized terrestrial mammals: rabbits and hares, marmots, ground squirrels, and — for larger females — occasionally young deer and pronghorn fawns. Fish are almost absent from their diet, and scavenging plays a smaller role.

Golden eagles achieve their flexibility differently: not by switching prey categories, but by matching body size to prey size, with females (larger) taking bigger animals than males. A jackrabbit-focused golden eagle in the Great Basin lives a fundamentally different life from a coot-eating bald eagle on a winter reservoir. The detailed comparison is in our bald eagle vs. golden eagle diet comparison and our golden eagle guide.

Frequently asked questions

What do bald eagles eat when there are no fish?

They move down the fallback hierarchy: waterfowl such as coots and ducks come first, then carrion (deer gut piles, roadkill, dead fish), stolen food from ospreys and other eagles, small mammals like rabbits and muskrats, and finally refuse. In some winter populations, scavenged food rivals live prey in importance.

Do bald eagles really steal food from ospreys?

Yes, and it is one of the best-documented behaviors in raptor ecology. An eagle chases an osprey carrying a fish, harasses it until the osprey drops the catch, then grabs the fish — sometimes before it reaches the water. At some locations a notable share of osprey catches are lost to eagle piracy, and eagles also rob each other regularly.

How much of a bald eagle’s diet is carrion?

It varies enormously by season and location. In winter — especially in northern areas with hunting seasons and fish die-offs — carrion can make up a large portion of feeding records, while in summer breeding territories with good fishing, live fish dominate. Think of carrion not as a fixed percentage but as the elastic component that absorbs shortages of everything else.

Why do eagles gather below dams in winter?

Dams keep water open and turbines stun fish, providing a concentrated food supply that stays available even when lakes freeze. Add the waterfowl that flock to open water and the bald eagle’s willingness to scavenge and steal, and a tailrace offers every tier of the fallback diet in one spot — which is why the largest winter eagle concentrations in the interior United States form at dam sites.