So far the only time I’ve seen the Common Gallinule (or as it had been previously named–the common moorhen) was on our trip down to South Padre Island years ago. Incidentally, when I took the pictures I first thought I had gotten a picture of a purple gallinule (as that as the only gallinule species listed on the scavenger hunt sheet that was handed out at the nature center’s visitor’s center). Spending more time looking at the pictures and getting ready to do research for the page, led me to realize that it was actually the common gallinule (or moorhen) with a chick that I’d gotten a picture of all those years ago.

These are crow-sized marsh birds that have charcoal gray feathers, white outer tail feathers, a red beak (with a yellow tip) and a bright red shield on their forehead. The young look similar, but lack the red shield and beak until they fully mature.
Those two key id features were hard to see in the pictures–but they were taken with my older and smaller Olympus digital camera that doesn’t have quite the same zoom capacity as my newer canon camera. That is why it took me years to realize I had originally misidentified the bird (I was going with what I’d been given).
The common gallinule is found throughout a good portion of the central and eastern parts of the United States (with small groups also being found in California, Nevada, Arizona, Utah, and New Mexico).

There is also a subspecies (Hawaiian gallinule or alae ula) found on the Hawaiian Islands (where it is listed as endangered due to habitat loss and predation).
In terms of where to spot them–head out to freshwater marshes, ponds, and lakes. You might hear them before you seem, but they’re easier to spot than some other members of the family–look for the ‘duck’ with the red shield and beak on the water. Though you might also spot them walking around as well foraging for insects.

Like other members of the Rallidae family, the common gallinule is an opportunistic omnivore in terms of its diet. It feeds on aquatic vegetation, seeds, snails, insects, and possibly small crustaceans as well. They will physically flip leaves over with their feet to look for insects and snails that could be hiding beneath them instead of foraging just with their beak.
Some interesting facts:
While their toes aren’t lobed or webbed, they’re still excellent swimmers.
They’ve been expanding their range northward for over the past 100+ years, to where now they’re breeding as far north as teh Maritime Provinces of Canada
Since I didn’t know that Oklahoma was part of their summer/breeding range (though considered a ‘rare breeding bird’), I will now be keeping my eye out for them on Boomer Lake, and also over at Sanborn Lake (once I start birdwatching there). I would say that a photography goal would be to get a crisper picture of them–so that the red shield and beak are prominent in the picture instead of appearing drab, in addition to possibly getting another picture of a parent and young foraging together.
Reference: https://www.allaboutbirds.org/guide/common_gallinule