Beauty is pain, the old saying goes. But for great bustards—the heaviest flying bird—a more accurate phrasing might be "beauty is poison." New research reveals that males of this species elect to consume small doses of a highly toxic compound to rid themselves of internal parasites and ultimately look more impressive for females.
Bird-loving researchers from the Spanish National Museum of Natural Sciences discovered the bustards' beauty secret after combing through hundreds of poop samples collected in the field and dissecting 25 of the birds. These investigations showed that male great bustards had consumed a conspicuously high amount of blister beetles, a foreboding-looking black and red insect that produces cantharidin, a highly poisonous compound that can kill many animals, including humans.
While females did eat a few of the beetles, an inordinate amount of those insects turned up in the males' systems. The researchers hypothesized that the bustards might be self-medicating for something, so they performed separate tests to see how various bacteria—including ones that cause sexually transmitted diseases in birds—might react to the poison. Sure enough, doses of cantharidin that turned up in the birds' poo was enough to kill off bacteria.
The researchers think that male great bustards seek out just enough toxic beetles to clear their systems of STDs and other diseases before mating season. Indeed, the team found the highest concentration of beetles around the time that males put on elaborate performances for picky females. As they point out in their paper, part of that choosing process involves the female inspecting the male's cloaca (i.e., bird butt)—"A white, clean cloaca with no infection symptoms (e.g., diarrhea) is an honest signal of both resistance to cantharidin and absence of parasites, and represents a reliable indicator of the male quality to the extremely choosy females." For males, it seems, getting the girl is worth the risk of death by beetle poisoning.