Tuesday, September 1, 2009

Feather Eaters

Grebe next-of-kin? (c) John AshleyMontana's grebe species look and act like small, economy versions of loons. They are unrelated to loons, however, and recent DNA studies have renewed an intriguing theory that the grebes are most closely related to -- are you ready for this? -- the flamingos. Not all taxonomists are convinced.

One intriguing behavior that is unique to grebes is that they regularly eat their own downy feathers. Grebe parents also feed feathers to their chicks. Why would they do this? The way Pied-billed Grebe chicks beg for feathers (below), you might think that feathers are as delicious as fish, their main food item. As it turns out, having a diet of mostly fish is the clue to solving this puzzle.

Adult Pied-billed Grebe feeding a downy feather to one of its chicks (c) John Ashley

But first, a little background.

Feathers are made of tough, keritinized proteins -- similar to beaks, claws and hair. So they are indigestible and don't provide any nutrition when eaten. Unlike a long flight feather, a downy feather has a tiny shaft and many soft plumes ("barbules"). They form the fluffy, insulating layer under the longer vaned feathers of all birds, including grebes.

Pied-billed Grebes have a short, chicken-like beak that features a handsome (especially to another grebe) black band only during the breeding season. They are common in Montana ponds and lakes that have emerging vegetation, like lily pads and reeds.

Grebes won't win any foot races, but they are torpedo-like underwater and can chase down small fish with relative ease. They'll also eat crayfish and aquatic insects, but the bulk of their diet is fish -- which brings us back to our feather-eating puzzle.

Adult Pied-billed Grebe feeding a fish to its young (c) John AshleyGrebes swallow fish whole. But fish bones are indigestible, and after a few meals a grebe might end up with a belly full of pointy fish bones and no way to get rid of them. So grebes also eat soft, indigestible feathers to line their stomachs and help form rounded pellets of feathers and bones, which they can then expel by coughing up.

These pellets are similar to the fur and bone pellets coughed up by owls and other rodent-eating raptors. The fish in Montana really don't have fur, in spite of what you may have seen on our truck stop postcards. So grebes add soft, flexible feathers to their diet to help them get rid of undigested fish bones.

Puzzle solved.

Behind the lens: Photographed from shore while sitting very, very still, with a Nikon D700, 500mm f4 lens and 1.4 teleconverter. Patience and persistence can work as well as a photo blind, especially when you're as cheap as I am!