Three birds on one nest: Bald eagles showcase surprising teamwork
We’re used to thinking of parents, especially non-human parents, as coming in pairs. For birds in particular, there are usually two standard models for parenting. Either the males play no role in egg incubation or chick rearing or the responsibility is split between the mother and father. In nature, these models generally hold true, but often the specifics are a little messier. Nesting in some species is also usually an affair of multiple family members caring for young. When I interned as a research assistant collecting data on Alaskan seabirds, I observed a small anomaly in normal bird behavior.
Black-legged Kittiwakes (Rissa tridactyla) are smallish sea birds that breed in the far north on both sides of the North American continent. Pretty nondescript gulls, kittiwakes have unique and interesting personalities if you spend enough time around them. I watched one particular nest with amusement. This nest had one male and two females watching the eggs. Although we didn’t observe the female laying her egg, it was obvious that one of the female birds was more invested in egg care than the other. One female diligently sat on the eggs and then fed the chicks when they hatched. The other female was rather negligent of her parenting duties, when she was alone in the nest, she rarely sat on the eggs or cared for the chicks. As soon as one of the other adult birds flew into the nest, it was show time and the formerly negligent female dutifully settled onto the eggs. Kittiwakes aren’t the only birds observed in a behavior similar to this.
Recently, MSN News reported on a bald eagle (Haliaeetus leucocephalus) nest in Illinois on the upper Mississippi River where three adult birds take turns caring for one nest. In the case of the bald eagles, there are two males and one female. Stewards of the Upper Mississippi River Refuge have observed all three adult members of the nest caring for eggs and young. Interestingly, both male eagles have been observed copulating with the female as well, so it’s unclear which is the biological father of the chicks.
The instance of a trio of bald eagles on a single nest is rare but has been recorded a few times before. According to the Audubon Society, the odd match of two males to one female predates the current arrangement. Originally at the nest, one female named Hope was observed with her mate, a male named Valor. Valor was a poor father, not tending to his nest and not bringing in much food. Because of the lack of food, Hope would leave the nest untended just to eat. Scientists and those observing the drama on live webcam thought the eggs may never hatch due to negligence but in the end they did. Unfortunately, Valor continued to neglect his duties and the chicks died before fledging. Then something strange happened.
Male bald eagles are usually territorial and hostile to each other, so it was a surprise when another male eagle showed up. The new male, later named Valor II, took up in the nest with Hope but Valor I wasn’t bothered and he continued hanging around the nest, still not contributing a lot to child care. Eventually though, Valor I learned better parenting skills, some attribute this to the influence of Valor II and in 2016, wildlife biologists had clear evidence of cooperative nesting among the three. The males would add sticks to the nest but Hope would often rearrange the branches, fixing the male’s attempts at home-making. Eagles are keen for prime real estate and are often loyal to an individual nest.
Soon after it was observed that the three eagles were cooperating nicely in chick care and nesting, two unknown eagles arrived on the scene. The eagles fought with the happy trio, probably trying to take the nest. The three fought hard and kept their chicks safe. Unfortunately, Hope was injured and not seen again, assumedly dying from the fight. The two valors continued caring for the chicks that fledged successfully that year. Typically bald eagles mate for life, only choosing a new mate after one of the pair perishes.
Interestingly, in the wake of Hope’s death, the two valors remained together at the nest, not seeking out their own separate mates. Instead, the current female arrived on the scene, a female named Starr by webcam viewers. Starr and the two Valors seem to be cooperating just as the original trio. Last spring, two chicks were hatched, one died rather quickly but the second fledged successfully. This year, three chicks have hatched and are being cared for by all three adult eagles. This is a rare case but not unheard of.
A paper published in Short Communications of the Raptor Research Foundation in 1995 describes observations of three adult bald eagles seen in a single nest twice in Alaska and once in Minnesota. The paper also details cooperative breeding among a trio in the Santa Catalina Islands. The phenomena described is sometimes known ecologically as ‘helper at the nest’.
Helpers at the nest have been observed in hundreds of bird species such as Brown Jays where an entire flock cares for a nest of four eggs laid by one female. Usually a helper at the nest is a previously fledged chick, helping care for a younger sibling. In crows, there can be as many as ten additional birds helping to raise a brood of chicks. With crows, the extra caretakers are typically male relatives of the male in the nesting pair. Interestingly, sometimes although rarely, the helpers are actually sneaking around. In crows 7% of offspring are fathered by ‘helpers’, according to Corvid Research. Even so, helpers do make things easier.
Some female birds, hummingbirds for example, raise the young themselves with no help from mates or otherwise. The diverse forms of life on earth, including the myriad examples of bird life are some of the things that make living here so beautiful.
Image Credit: Stewards of the Upper Mississippi River Refuge/National Audubon Society