Regular observers are aware by now that only the oldest two of three eaglets now occupy the nest. From notes submitted to this web page about six days ago, the largest chick likely killed the youngest. We've been watching closely to see a third chick, but haven't for almost a week. As we reported in our biologist's notes, siblicide is a natural occurrence for bald eagles and other birds of prey. What you are observing on the web camera is unedited, unsanitized, real-time nature - survival of the fittest. If you have been lucky enough to observe a feeding bout, you have a sense of the intense competition between the siblings.
Fish, birds, and other animals are being killed by the adults several times daily to feed the hungry chicks. At this age, the adult eagles are still feeding the chicks, but soon the chicks will start to learn how to feed on their own. Adult eagles require about one pound of food each day. The demands of both adults and growing chicks require several pounds of prey are procured daily. Predation is a natural part of the cycle of life. Life in the nest can be a tough experience and we may loose other chick(s) before this nesting cycle is completed.
I just finished watching a feeding this afternoon. The oldest "A" chick is noticebly larger and more aggressive. Naturally it elbowed its way to be fed first. The "B" chick is smaller and had to wait its turn, but both received a full meal. Both of the remaining chicks seem to be growing at a normal rate. You can determine if the chicks have been fed recently by looking to see if their crop is full. The crop is a food storage organ, which when full creates a bulge at the top of the chest (just under the beak). Adult eagles often consume dead animals (or carrion), which are often too large to carry away. The crop allows birds of prey to consume a large meal and fly elsewhere to digest at their favorite perch.
We received an interesting inquiry from Maggie, a second-grade observer from Bangor, Maine, about eagle cleanliness. After feedings, watch for the young eaglets to back up to the edge of the nest to defecate. This is the eagles' way of keeping a clean nest. The whitewash, or "mutes" as they are called, begin to cover the ground below the nest along with a collection of fish carcasses and bird feathers. The adult eagles still rearrange sticks in the nest and toss uneaten carcasses over the side. Some of the uneaten prey gets buried in the nest bowl. The chicks are getting to an age where they may play with an eider duck wing or fish tail. As the chicks get older the nest platform will be well-trampled by their activity. The adults will continue to freshen the nest periodically with a sprig of white pine.
What kinds of prey are these bald eagles bringing to the nest? We'd like to hear about your observations. For years, we gathered food remains at the base of eagle nests to better understand eagle diets in Maine. Over the years Charlie Todd identified 64 different species of vertebrates. Fish made up more than 75% of remains and were the predominant prey at inland nests. Coastal sites relied more heavily on birds and mammals. When we installed the web camera in mid-winter we found the remains of eider ducks and cormorants at the base of the nest.
Coastal eagles feed at a higher level on the food chain than interior birds. Fish-eating ducks (like mergansers) and cormorants have higher contaminant loads than fish. Thus, our coastal eagles have a greater likelihood of accumulating contaminants like PCBs and DDT. Even at this age, the young chicks in this nest already have detectible contaminants in their blood. They received some contaminants in the egg, but are receiving additional contaminants from their food. We will write more about contaminants and how they affect eagles in future biologists notes.
Mark McCollough, U. S. Fish and Wildlife Service