Ever see a flock of ducks in a circle seemingly in a feeding mode – even a frenzy?
That is was I observed on a local pond last week. I’ve observed this type of feeding in the past, usually with shovelers. The first time I ever took notice of this type of feeding was at Lower Klamath National Wildlife Refuge about 25 years ago. The ducks were spoonies.
Last week I spotted a group of widgeon doing this. Here’s a photo.
These widgeon were definitely feeding. My theory is that they were feeding on invertebrates that live near the bottom of the pond. Because these are dabblers, they don’t dive for food so critters on the pond bottom are not available to them. Somehow the ducks have learned that by feeding in a circle, the food rises towards them.
The reason for this? As they paddle towards the center of the group (circle) the ducks paddle water away from the center of the circle. This creates water movement away from a point at the center. As the water moves away, it must be displaced by other water. The displacement causes water to rise from the bottom. This is a similar effect to a low pressure weather system.
Water movement from bottom to top brings up the critters. I think this type feeding is more commonly found in winter as food sources diminish. Here’s another photo.
If you click on the photos they will enlarge.