Bald Eagles primarily eat fish, and you will often find their nests near a good water-based food source. They are also opportunistic eaters, meaning they not only catch live prey, but will steal food from other small birds or mammals, or scavenge carrion (roadkill, dead birds or mammals). They will also eat: waterfowl; small mammals such as rodents, squirrels, raccoons, rabbits, moles and nutria; reptiles including frogs and turtles; and take parts of larger mammals such as deer. At many nests with cameras, we have learned they will also dine on food stolen from trash or landfills, if one is close enough. If you ever come upon a flock of large birds, likely vultures, dining on carrion, look closely and you may see a Bald Eagle in the mix.
An eagle can carry food that is about one-third of its body weight, which equates to approximately two to three pounds. They normally eat one-half to one pound of food per day. Fish are normally totally digested, and they are able to digest bones which provide very important nutrients, especially calcium for the female, which is needed during her fertile period for egg formation. They have acid in the digestive system that helps to dissolve bones, and most are completely digested. Fur, feathers and any undigested food particles form what is called a pellet in the gizzard that is later expelled. Most eagles will expel pellets in the morning after digesting their food from the day before.
A Bald Eagle’s digestive system has an area called a crop that is unique to birds. This is an area in the esophagus that can temporarily hold up to two pounds of food, enabling a Bald Eagle to go days without eating. When the eagle has had a large meal, you can sometimes see the crop bulging out on the throat and chest area. The bird moves the food from the crop into the stomach, which is about the size of a walnut in an eagle, through a maneuver of opening its beak and swallowing (which looks to us like a yawn).
The eagle has a strong beak made for tearing the food into manageable pieces. The tongue contains two backward facing barbs that assist swallowing by moving food from the front of the beak and tongue to the back of the tongue. There is also a hole, the glottis, on the tongue that is part of the respiratory system. By pushing food into the back of the esophagus and past that opening, it can eat large pieces without choking. They do not chew their food but swallow each piece, or in the case of a small fish or rodent, swallow it whole.
Do raptors need to drink water? The simple answer is that although you may see a raptor take a few sips of water, they don’t need to drink. Under normal circumstances, they get all the water they need from their food. The more complex answer is that they get all the water they need from the water contained in the food itself and from metabolic water, which is water created inside a living organism through their metabolism by oxidizing energy-containing substances in their food.
Once the food is moved from the crop into the stomach, there are two parts of the stomach that aid in digestion. The first is the proventriculus where digestive juices help to break down the food. This joins to the ventriculus (the gizzard) that grinds up the food and bones. The gizzard contains gravel and grit to aid in this grinding. The food then moves to the small intestines where it mixes with bile. Eagles also have a liver that helps to break down any fat and detoxify the food, and moves the nutrients into the bloodstream. After passing through the intestines, the waste is excreted through the cloaca, the single posterior opening for an eagle’s digestive, urinary and reproductive tracts.