In the column “Since You Asked” in every issue of BirdWatching, Contributing Editor Julie Craves answers readers’ questions about birds and bird behavior. Here is a question from our March/April 2019 issue.
Q: I thought that people aren’t supposed to eat apple seeds because they contain cyanide. I read that hawthorns are related to apples and also have cyanide in the seeds. But I see birds eating hawthorn fruit all the time. Can birds eating hawthorns 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 the seeds when they are chewed or damaged. The amounts of amygdalin in the seeds of most fruits is small, and many seeds would need 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 opportunity for hydrogen cyanide to be released.
Amygdalin is just one of the cyanogenic compounds commonly found in many bird-consumed fruits — both in the seeds and in the pulp. At least some bird species, such as the Cedar Waxwing, are more tolerant of these compounds than mammals because their digestive processes differ. It is believed that various chemicals are present in seeds and fruits to discourage consumption by mammals, which would thwart the reproduction of the plant, while birds are able to fulfill their role as seed dispersers.