The Case of the Barfing Blue Jay

For some predators, chowing on a monarch butterfly can have digestive repercussions.

A naive blue jay is offered a monarch that contains cardiac glycosides stored from the milkweed plant that the caterpillar had eaten. Image copyright Lincoln Brower, Sweet Briar College
A naive blue jay is offered a monarch that contains cardiac glycosides stored from the milkweed plant that the caterpillar had eaten. Image copyright Lincoln Brower, Sweet Briar College

During a recent show, SciFri’s Flora Lichtman discussed monarch butterflies with Lincoln Brower, a biology professor at Sweet Briar College in Virginia. During the conversation, Brower mentioned a photograph that he had taken of a “barfing blue jay,” which had just suffered a distasteful experience dining on a monarch. We thought you might be curious to see the image:

About 12 minutes after having ingested a toxic monarch, this jay (different from the one above) vomited several times, ridding itself of what otherwise would have been a potentially lethal dose. Once a jay has had this negative experience, it learns to avoid subsequent monarchs on sight alone. Image copyright Lincoln Brower, Sweet Briar College
About 12 minutes after having ingested a toxic monarch, this jay (different from the one above) vomited several times, ridding itself of what otherwise would have been a potentially lethal dose. Once a jay has had this negative experience, it learns to avoid subsequent monarchs on sight alone. Image copyright Lincoln Brower, Sweet Briar College

Why the upchuck? Monarchs feed on milkweeds, plants which contain chemicals called cardiac glycosides that the insects absorb. While the toxins don’t harm the butterflies, they taste bitter and can cause vomiting in birds that chow on monarchs.

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Monitoring the Monarchs

Some bird and mice predators, however, figure out a way around the poison—either by avoiding monarchs once they’ve had an unpleasant experience, or by pecking or nibbling at potential monarch meals to gauge the insect’s toxicity level. If the butterfly tastes “clean,” it’s dinner.

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About Julie Leibach

Julie Leibach is Science Friday’s managing editor of online content. She is a huge fan of sleep and chocolate.

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