The Things You Learn: Brood Parasites

It goes without saying that I find the internet to be a great source for expanding one's knowledge. Used properly, a person can learn a thing or two along the way. Yesterday morning, while enjoying my usual two cups of hot brewed beans - with a touch of hazelnut cream - I was perusing A Snail's Eye View and a post about cooperative breeding among Dusky Moorhens. Being quite familiar with Common Moorhens, which were, well, pretty common around just every pond or marsh back in Florida, it got me wondering if the moorhen I knew behaved in a similar manner. A visit to the Common Moorhen pages at Cornell's Birds of North America Online ($ subscription) revealed the information and it turns out that they, like the Dusky's, also engage in cooperative breeding. What I didn't expect to find is that, in addition, Common Moorhens can be both victims and perpetrators of brood parasitism! I always thought that was mainly a cowbird thing. Show's what little I know!

In Kevin's continuing education, I learned there are two types of brood parasitism: conspecific (or intraspecific), where a female lays eggs in the nest of another female of the same species, and interspecific, where eggs are laid in the nest of a different species. Rob's Idaho Perspective has a post on intraspecific brood parasitism that discusses moorhens; the behavior in this species is, as I would learn, not that uncommon. It got more interesting when I learned in the BNA article that, though reports are rare, Common Moorhens both practice and/or are victims of interspecific brood parasitism, too. (The terminology used by different ornithologists was initially a bit confusing, with "intra" and "inter" sounding almost the same, but meaning the opposite.)

Interspecific brood parasitism uncommonly reported. One record each of moorhen as a nest parasite of Purple Gallinule in Texas, of Black-headed Gull (Larus ridibundus) in England, of Boat-tailed Grackle in S. Carolina, and of Yellow Bittern (Ixobrychus sinensis) in Japan (Cottam and Glazener 1959, Jones 1988, Post and Seals 1989, Ueda 1993). Moorhens have been victims of brood parasitism by Ruddy Ducks (Oxyura jamaicensis) in Iowa and Least Bitterns (Ixobrychus exilis) and Fulvous Whistling-Ducks (Dendrocygna bicolor) in Louisiana (Fredrickson 1971, Helm et al. 1987). In Texas, a moorhen nest with eggs was taken over by a pair of American Coots; another moorhen egg was subsequently laid in nest while coots produced their clutch (Cottam and Glazener 1959).

Bannor, Brett K. and Erik Kiviat. 2002. Common Moorhen (Gallinula chloropus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology;Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/685
                                                                      

One commonality is that each of these species generally prefer the same sort of breeding habitat: marshes or ponds with lots of emergent vegetation in which to hide the nests. Purple Gallinule or American Coot don't seem that far fetched; they are pretty close relatives in the grand scheme of things, after all. I can even come to grips with the bitterns and the ducks. But the gulls and, especially, the Boat-tailed Grackles - now that is just weird.

Oh well, if a female moorhen can get a grackle to do all the work and, in the end, she has more surviving offspring, why not? When it is all said and done, that is what it is all about.

If I had a lot of time on my hands, it would almost be fun to dig even deeper into the subject. For example, a quick search found a short article about brood parasitism in ducks:

The Redhead appears to be our most persistent parasitic duck. In one study on artificial islands in reservoirs in Alberta, Redheads parasitized 19 percent of 685 duck nests, laying an average of 2.68 eggs per parasitized nest. Mallard nests were most frequently parasitized, but the percentage of parasitic eggs per nest was highest when Lesser Scaups were the hosts.

And that article links to yet another (this could be an endless endeavor, no?) that indicates brood parasitism occurs "in about 1 percent of bird species." Meaning there are roughly 100 species world-wide that are one of the two types of brood parasites (or, at least in the case of Common Moorhens, both) - a far greater number than I would have imagined.

Ol' Mother Nature is certainly full of surprises . . .