By Katherine Dale, PhD student, Ecology & Evolutionary Biology, University of California Santa Cruz
Take a walk along the San Lorenzo River and you’ll almost certainly see black, football-shaped birds speedily swimming around. They might be gently chortling to one another and perhaps probing the reeds with their white bills looking for vegetation to nibble on. Upon first inspection, you might think that these water-loving birds are ducks. However, these are American coots (Fulica americana), which are more closely related to sandhill cranes and rails than to ducks. Coots are a common sight in freshwater ponds, lakes and rivers in North America.
Take an American coot out of the water and it’s easy to see how they are different from ducks. Coots have incredibly long toes and feet for their bodies and their feet aren’t webbed – instead, they have lobes of skin around each toe that help them to move through the water. To allow them to comfortably walk around on land, the lobes cleverly fold up when the bird lifts its foot. Their large feet help to stabilize them on mud and marsh soil, where they occasionally feed. As omnivores, submerged vegetation, insects and fish eggs make up the bulk of their diet, but they’ve also been known to steal food from ducks! In an interesting nesting pattern, male birds construct floating nest platforms amidst the grasses on the edge of the river.
Coots are sometimes written off as “just another common bird,” but they actually demonstrate some remarkable behaviors. Coots are brood parasites. Brood parasitism is when birds lay their eggs in other birds’ nests, thus avoiding the costs associated with parenthood (raising kids is hard!). This phenomenon is relatively common among birds, but the surrogate parents can rarely identify the imposter even when the chicks are of different species. American coots are unique parasites because they parasitize the nests of other members of their own species. This introduces a game-like aspect to nesting, where coots must decide how many eggs to lay in their own nest, versus the nests of other pairs. This tradeoff may help to explain why coot clutch sizes aren’t larger¹.
Interestingly, researchers at UC Santa Cruz have determined that coots can recognize their own young and kick out interlopers². How do they do it? Dr. Bruce Lyon and his team observed that coots use the chicks hatched on the first day as a “model” for what the rest of the chicks should look like. If subsequent chicks don’t look like the chicks hatched on the first day, they are actively rejected.
So now you know – those black bobbing birds on the San Lorenzo aren’t ducks at all – they’re a charismatic bird that has a variety of unusual traits. And the next time someone calls you an “old coot,” thank them – they just complimented your remarkable capacity for learning!
Questions? Email Kat at firstname.lastname@example.org.
- Lyon, B. E. Optimal clutch size and conspecific brood parasitism. Nature 392, 380 (1998).
- Shizuka, D. & Lyon, B. E. Coots use hatch order to learn to recognize and reject conspecific brood parasitic chicks. Nature 463, 223 (2009).
- Photo: “American Coot (Fulica americana) family american-coot-chicks-6-4-07” by Mike Baird is licensed under CC BY 2.0