|The Question: Can you tell me what might have caused the wound on this hummingbird? It looks like it had open heart surgery!
Submitted by: Irene, Ontario, Canada
(click on photos and graphics to expand)
The Short Answer: Irene, that’s a brood patch on a female ruby-throated hummingbird (Archilochus colubris). Birds that incubate eggs lose their breast feathers when they are nesting. Otherwise, feathers, which make great insulation, would prevent the eggs and chicks from being warmed as efficiently by the parent. So what you saw on this hummingbird is perfectly normal and nothing to worry about. This time of year, the parents don’t need the insulation, so losing some breast feathers for a while doesn’t bother them. They’ll grow back before the weather gets cold in the fall.
More Information: The loss of breast feathers is triggered by hormones released at the time of egg laying. Some birds don’t ever lose breast feathers for incubation. This includes species like the brown-headed cowbird (Molothrus ater), which lays its eggs in the nests other birds, birds like gannets that warm eggs with their feet, and the males of many species, including ruby-throated hummingbirds, in which the female does all the incubation work. Female ruby-throated hummingbirds build the nest of plant material and spider webs and carefully camouflage it, a process that takes a week or more. They lay the eggs, of course, typically two. They sit on the eggs, warming them against the bare skin of the brood patch, for 12-14 days. Once the eggs hatch, it takes 18-20 days for the chicks to begin flying. The female feeds the chicks for another 4-7 days after they leave the nest and then they’re on their own. As with many birds, the chicks actually weigh more than the adults at that point, but their weight drops sharply until they get good at feeding themselves. While female ruby-throated hummingbirds are doing all that chick-rearing work, the males are defending food sources and trying to attract additional females to mate with – and keeping all their breast feathers the whole time. It’s only ever the females that look like they’ve had heart surgery.
Sources: Weidensaul, Scott, T. R. Robinson, R. R. Sargent and M. B. Sargent. (2013). Ruby-throated Hummingbird (Archilochus colubris), 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/204
Gill, F. B. (1990). Ornithology. New York: W.H. Freeman.[cite]