Pochard feeding behaviour (1 Viewer)

[navybloke]

I visited Abberton Reservoir (southern England) today to see a drake Canvasback which was associating with a flock of several hundred Pochard. The flock’s feeding behaviour - at least, I presume it was feeding behaviour - was like nothing I’ve seen before.

For periods of 10-15 minutes the whole flock would bunch extremely closely together and move purposefully and quickly in one direction, albeit with regular changes of direction during a feeding period. The ’front ranks’ of the flock would be diving intensively as the flock moved, with the ‘rear ranks’ formed by birds surfacing after the main body of the flock had passed overhead on the surface. The ‘front ranks’ were so tightly packed as to make picking out individual birds impossible, and at the trailing edge of the flock up to three or four birds would surface every second, occasionally up to 5m behind the main group and hurrying to catch up. Given the speed of travel, I judge (very roughly) that individual dives lasted no longer than 30 seconds.

It’s difficult to describe, but the constant activity looked like a coordinated conveyor belt in response to a concentrated and mobile food source under the surface. When feeding stopped and all birds were on the surface, it became apparent that up to half of the flock was dived at any one time. The feed/pause sequence was repeated for the 90 minutes that I observed the flock.

I’m curious about possible explanations for this behaviour given that (as far as I know) Pochard feed on submerged plants, invertebrates and molluscs - not bait balls!

 

[navybloke]

The feeding behavior you observed is known as "chain diving" or "looping", I know it is a common strategy employed by diving ducks and includes Pochards, to efficiently capture food sources that are scattered or patchy in distribution.

So here we go: by diving in a coordinated and synchronized manner, the flock creates a disturbance that stirs up the bottom sediments and dislodges potential prey, making it easier for them to capture. The tight packing of the flock also helps to concentrate the prey, further increasing their chances of success.

The speed at which the flock moves and the short duration of individual dives suggest that they are primarily targeting small invertebrates, such as midge larvae, that are abundant in the shallow waters of Abberton Reservoir. These invertebrates are typically found in the bottom sediments and are stirred up by the flock's diving activity.

The fact that the flock only feeds for short periods and then spends time resting on the surface is interesting and I see it that they are not targeting a particularly dense or concentrated food source. Instead, they are likely following a patchy distribution of prey, moving from one area to another as they deplete the available resources

What a great response - thank you so much, that's really informative and interesting. Much appreciated.