The San Francisco Bay Trail is a series of flat gravel trails that circle the namesake system of creeks, sloughs, water retention ponds, salt ponds, and open bay waters that line the interior of the peninsula. These scenic pathways provide visitors with an up close opportunity to observe the habits of water birds that visit the SF Bay.
One such habit for hikers along the Bay Trail to look out for is cooperative feeding among water birds. Cooperative feeding is a behavioral strategy where groups of the same species of birds work together to locate, capture, or stir up prey. While most bird species feed alone, some, such as the northern shoveler (a type of dabbling duck) and the American white pelican, optimize by foraging in large groups.
Cooperative feeding among birds
In cooperative feeding, birds use synchronized actions—like swimming or flying in formation—to concentrate prey in a smaller area. This strategy makes it easier for each individual to capture food while expending less energy than they might if feeding alone.
Feeding circles: northern shoveler
The northern shoveler (Spatula clypeata) is a type of dabbling duck distinguished by its unique, elongated bill that broadens at the tip. This shovel-shaped bill is specialized for straining small organisms from the water’s surface, including plankton, crustaceans, and aquatic insects. Northern shovelers can often been seen swimming in open waters with their bills skimming the surface for food.
Northern shovelers create a feeding circle by gathering into a tight group in the water. Each duck then paddles, typically in a counter-clockwise direction, within the circle. The collective action of the northern shovelers creates a funnel in the water that brings small invertebrates to the surface. The ducks then use their comb-like bills to strain out the water before ingesting the tiny aquatic organisms.
This feeding circle takes advantage of a collective effort to disturb the water, making it a more energy efficient way of bringing food to the surface for capture.
Collective herding in American pelicans
Unlike brown pelicans, which plunge-dive for fish, American white pelicans (Pelecanus erythrorhynchos) feed by dipping their large pouches into the water’s surface to scoop up prey.
American white pelicans can be seen foraging both as individuals and in large cooperative herding groups. When American white pelicans feed as a group, they will work together to herd fish into a dense ball, making it much easier to scoop up fish.
