Why Birds Can Eat Hawthorn

In the “Since You Asked” section of each issue of BirdWatching, editor Julie Craves answers readers’ questions about birds and their behavior. Here’s a question from our March/April 2019 issue.

Q: I thought people weren’t supposed to eat apple seeds because they contain cyanide. I read that hawthorns are related to apples and also contain cyanide in the seeds. But I see birds eating hawthorn fruit all the time. Can birds that eat hawthorn be poisoned? — Chris Meier, Louisville, Kentucky

A: The seeds of many plants, including cherries, almonds, apples, crabapples, and hawthorns, contain varying amounts of a compound called amygdalin. Hydrogen cyanide can be formed and released from seeds when they are chewed or damaged. The amounts of amygdalin in the seeds of most fruits are low, and many seeds would have to be chewed and eaten by a human to cause harm. Although obviously much smaller, birds that eat hawthorn and crabapple fruits swallow them whole, and the seeds pass through the birds’ digestive systems intact, with little or no possibility of hydrogen cyanide release.

Amygdalin is just one of the cyanogenic compounds commonly found in many fruits eaten by birds, both in the seeds and in the pulp. At least some species of birds, such as the cedar waxwing, are more tolerant of these compounds than mammals because their digestive processes differ. Various chemicals are thought to be present in the seeds and fruits to discourage consumption by mammals, which would thwart the reproduction of the plant, while birds are able to perform their role as seed dispersers.