Great Bustard males have a secret strategy to win the hearts of females concerned about sexually transmitted diseases: poisonous beetles.
By Rex Graham
By April, male Great Bustards, one of the largest flying animals on the planet, have sorted out the competitive hierarchy among the males gathered at courtship leks. The biggest males with the most enviable whiskers and the showiest neck feathers have claimed their rightful places at prime lek locations.
Great Bustards and STDs
What scientists didn’t know until recently is that males self-medicate.
Curious females arriving at leks care about a prospective mate’s age: older is more attractive. Whiskers, feathers and other ornaments are eye-catchers. However, the ladies don’t want to catch sexually-transmitted diseases (STDs). The males seem to know.
Their scintillating displays conclude by bending forward and exposing their sperm-swollen cloacas. The cloaca is the combined opening for the intestinal, reproductive, and urinary tracts of birds. It is a preferred site for mites and lice. The females eagerly inspect the organ for any sign of infestation.
Females actually give the cloaca of each suitor a few pecks just to be sure. They are among the pickiest of all birds.: about 90% of all male overtures are rebuffed, and his cloaca display is each bird’s moment of truth.
If a Great Bustard has a kind of digestive disease, his cloaca will look awful. His pure white feathers down there make an accurate assessment easy.
What the females can’t see is what male Great Bustards eat. Researchers reported in PLoS ONE that leading up to breeding season, male Great Bustards selectively eat a large number of nasty tasting, poisonous blister beetles. The males ignore harmless invertebrates, preferring blister beetles full of cantharidin, a highly toxic chemical.
Bustard males self-medicate with blister beetles
Blister-causing cantharidin is produced by many species of blister beetles, including the Spanish fly, which is claimed to have aphrodisiac properties. The chemical irritates the human genitals, resulting in increased blood flow. Its use as a prescription drug for impotence has been banned because of its highly dangerous health effects.
For Great Bustards, the benefits of eating blister beetles must be balanced against the toxicity of cantharidin, which can be lethal for the bird. Male birds, which eat many more of blister beetles than females, must somehow balance the toxic effects of the chemical against the benefits of reducing its load of harmful bacteria and parasitic worms.
A team of scientist at the Museo Nacional de Ciencias Naturales in Madrid, Spain, writing in PLoS ONE said that the male Great Bustards preferential ingestion of blister beetles amounts to self-medication to gain a courtship advantage.
“We suggest that males use self-medication not only to overcome the pathogen burden during a strenuous display, but also to withstand the close scrutiny of choosy females, showing a clean cloaca as honest signal of health, increasing their mating success,” the researchers wrote. “The expected relationship between self-medication and subsequent greater mating success, necessary to demonstrate a direct link with sexual selection, is extremely difficult, if not impossible to measure in great bustards at present, but it could be explored in other species. In spite of the universality of sexual selection theory, self-medication has probably been overlooked as a sexually-selected mechanism enhancing male fitness.”
Great Bustard decline in Europe, Asia & Africa
A BirdLife International assessment of the Great Bustard notes that hunting and habitat loss has hurt the bird’s population in Central Asia and most of its remaining habitat. However, populations in the Iberian Peninsula “have stabilized and possibly increased.”
A lack of genetic diversity is imperiling small populations on the periphery of the bustard’s historic range in places like Portugal, Turkey, Iran, Kazakhstan, Russia, China and Mongolia. The small population in Morocco is declining as well. “Available counts indicate a severe population decline (62% in the last 15 years), as well as a contraction of the species’ distribution,” researchers from Spain reported in the journal Endangered Species Research.
The U.K.’s Great Bustard Group re-introduced 33 birds the U.K. in 2014. At least 12 have been located in spring 2015. In July 2016, the group said that it hoped one recently sighted wild-bred female chick “will be the first of several to successfully fledge this year.”
Males regularly display at two sites in Wiltshire. Some adult birds are occasionally injured in collisions with fences. Elsewhere, bustards die in collisions with power lines and vehicles. Local U.K. farmers, keepers and birders share their sightings with the Great Bustard Group.
— Rex Graham (@TopBirdingTours) September 1, 2016