Some Cooperation in the Field Gets Everyone Fed!

One of my favorite things in 9th grade biology/marine bio was the study of symbiosis~ the way two organisms had evolved together to have a relationship that benefitted one or both. So it was a delight to watch three species interacting yesterday. Hooded Mergansers were feeding in the impoundment, and they were being followed closely by a pair of snowy egrets and a small gull. They really seemed to be cooperating with one another, and I would call this version of symbiosis mutualism, where both (or in this case, all) species benefit from the interaction.

Bonaparte's Gull

This pretty little gull flies like a tern and has a more delicate frame than some of our other winter gulls. I only ever see them doing two things: 1) diving in the waves when it’s rough:

… and (2) following ducks around the impoundment.

Mutualism: Everyone should benefit

The snowy egrets are patrolling the edges of the water. Sometimes their bright feet look like lures to underwater fish, so maybe that’s a benefit to the ducks. The ducks create an underwater ruckus that sends prey in the directions of the other birds, so that’s a benefit to both of them. And if they all work together to expend less energy, that leaves more calories for each of them to spend on keeping warm.

Need a Longer Look?

If you’re a teacher trying to demonstrate any of these concepts or you want your students to come to conclusions, here’s a longer 2.5 minute version, unedited and unnarrated. (and oops, I left a little intro and outro music in there.)

Other gulls do this too

Here are some photos of a ring-billed gull doing the same thing with a flock of scaup, feeding in exactly the same place. We had a huge flock of scaup here in 2013, when the impoundment was low for the repairs.

Kleptoparasitism also happens.

This behavior where gulls hover hoping for castoffs is not limited to this particular species. Kleptoparasitism, where one organism straight up steals from another one, is also something we see around here. The eagles will steal from the ospreys, and this gull was harassing a pelican in Dewees Inlet, even landing on its head waiting for the pelican to grab a fish.

Snowy Egrets are used to Feeding in a Crowd

It’s not uncommon to see a bunch of snowy egrets feeding together when conditions are right, and they are one of the species that follows strand-feeding dolphins, anticipating leftovers on the shore.