Here’s a great ZeFrank video, “True facts about parasitic birds”, that’s both visually compelling and biologically accurate. As time passes, ZeFrank seems to get more and more into the biology and evolution of the animals and behaviors he describes and become less involved in being clever. And that’s great, for the videos are now both informative and clever.
This would be a great video to show to a class on evolution or bird biology, and I’ve sent it to reader Bruce Lyon, an evolutionary ornithologist at UC Santa Cruz, as well as and reader and contributor to this site. One of Bruce’s specialities is brood parasitism, and if you have questions for him, put them below (I can’t guarantee he’ll answer, as it’s too early for me to ask him!).
In this 11-minute video, ZeFrank (whoever he is) takes up the issue of “brood parasitism”: the habit of some species of birds to lay their eggs in the nests of birds of other species. (Some also parasitize nests in their own species.) There’s an obvious evolutionary advantage to letting another bird raise and feed your own offspring while you go on and spread your genes by parasitizing another nest.
As ZeFrank shows, this leads to an “arms race” in which the parasitized host is selected to eliminate the eggs dumped in their nests by parasites, while the parasites evolve not clever behavioral strategies and morphological traits to “hide” their eggs and chicks by evolving parasite eggs and chicks to resemble those of the hosts. Even the behavior of parasitic chicks has evolved to resemble the behavior of the offspring that a mother would normally have, deceiving the mom about which chicks are hers. Thus the video instantiates many of the features about evolution that we’ve learned: arms races, convergence (resemblance of parasite eggs and chicks to those of the unrelated parents), the efficacy of natural selection, and the remarkable exactness with which selection can approach an “optimum” (resemblance of parasite chicks and eggs to those of the hosts.)
Be sure to watch the whole thing to see the experimentation that biologists have done on this phenomenon, videos of parasites removing host eggs from the nest (8:00), the feeding a a giant parasite chick—much bigger than the mother!—by a tricked host (9:05), and the “mafia theory” about why some nest parasites will return and destroy a host’s nest if the host has not cared for the parasite’s young (9:50).