The burning question of the day popped up this morning while I was making coffee at 4 am (I’m a light sleeper) and listening to a BBC program on monarch butterfly migration. These beautiful North American butterflies are right now heading south along with all those feathered vertebrates to their wintering grounds in Mexico and parts of central California. My yard in Oklahoma is en route. A population of monarchs winter in the Monterey pines of Pacific Grove, California, and the sight of tree-covering clusters of orange-and-black butterflies bending down the branches is really something to see.
The key phrase here is “orange-and-black”. It’s a color scheme known as aposematic and is used as a warning to predators: their target may be toxic. Having fed on lovely but toxic milkweed when they were caterpillars, the adult butterflies taste bad and don’t get eaten too often, usually by mistake (and I’m picturing some young, inexperienced bird spitting and making a face- a nice image). I’ve always heard that nothing preyed regularly on them, but according to Chip Taylor, professor of entomology at University of Kansas and director of Monarch Watch, and Bill Calvert, an independent monarch biologist, there are three predators on the monarch’s Mexican wintering grounds, one species of mouse and two birds: the black-backed oriole and the black-headed grosbeak. What do these birds have in common (besides the word “black” in their names)? They are both black-and-orange.
Which led me to wonder: are these two species are eating monarch butterflies for toxic protection from their own predators? Are there any toxic birds out there, anyway? The answer is yes, one known case.
The New Guinea Pitohui (a name that sounds like what a predator does when spitting one out) is the only known example of a poisonous bird. It’s skin and feathers are toxic when eaten. It’s also black-and-orange. According to a recent study by the California Academy of Sciences, the pitohui may get its toxins by eating choresine beetles. Fascinating stuff. Further reading here and here.
So the question of the day is this: are black-backed orioles and black-headed grosbeaks toxic? Who wants to test this one out? And will someone please check on that mouse?