Why Grebes Eat Feathers

Grebes, as a group, are known for eating feathers – usually their own.  The obvious question is – why?  There would be virtually no nutritional value in a feather.

 

Clark’s Grebe eating a feather

I’ve photographed four species of grebes – Western Grebe, Clarks Grebe (these two are very similar), Pied-billed Grebe and Eared Grebe.  I’ve been able to document feather eating in all but the Eared Grebe.

 

 

Western Grebe parent feeding feather to young

Over a period of perhaps a half hour I watched this adult feed several feathers to the chicks, who seemed almost as eager to consume the feathers as they did the fish provided by the parents. 

 

 

Western Grebe chick reaching for a feather from its parent 

Feathers are fed to the young almost immediately after hatching.  In fact, feathers are very often the first item eaten by newly hatched chicks of many grebe species.

The purpose(s) of feather eating is unproven but evidence suggests that the behavior has these benefits for the birds. 

1. Some of the ingested feathers form a plug in the pylorus, between the stomach and small intestine, which acts as a strainer to keep fish bones in the stomach long enough to be completely digested. 
2. Most swallowed feathers end up in the stomach lumen, mixed with food.  They eventually (along with any indigestible matter) form pellets that are ejected through the mouth.  The continuous passage of these pellets through the upper digestive system minimizes the buildup of a variety of parasites that are very common there and plague grebes. 

 

Pied-billed Grebe eating a feather 

Most of the feathers grebes eat are their own, pulled out during preening.  However, if there are many grebes on a  pond, lots of these feathers end up floating on the water.  When a grebe sees one of them it will very often eat it, whether or not it’s from that bird or another.  In my experience, whenever a grebe notices one of these feathers slowly floating by it invariably plucks it out of the water and gobbles it down. 

Virtually all of the feathers are small, soft, contour feathers from their flanks – not the larger quill feathers.  Grebes continually molt these flank feathers, probably as an adaptation that provides a constant supply of feathers for pellet formation. 

 

Pied-billed Grebe about to consume a feather 

In post-mortem exam, feathers may form as much as 52.5% of total stomach contents in Pied-billed Grebes, so obviously feather ingestion plays a significant role in the normal functioning of the digestive tracts of grebes. 

Ron  

 

 Source: The Birds of North America, Online (pay site)