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Cuckoo helps nestmates by releasing awful stench

March 21, 2014
Courtesy of Uni­vers­ity of Neuchâ­tel
and World Science staff

Cuck­oos are the bird world’s most no­to­ri­ous freeload­ers: many lay eggs in the nests of oth­er bird spe­cies, lead­ing un­wit­ting par­ents to raise a lit­tle cuck­oo while their own young lan­guish or die.

But French and Span­ish bi­ol­o­gists have found one pret­ty cuck­oo spe­cies with a help­ful side. When threat­ened, its ba­by emits a re­pug­nant stench that wards off preda­tors—help­ing to pro­tect nest-mates in the pro­cess. This scent in­cludes mo­le­cules that smell like vom­it, sul­fur, death and fe­ces all rolled in­to one; preda­tors won’t tou­ch food tainted with it.

Infant crows beg for food while a baby cuc­koo lies to the side. (Pho­to by Vit­to­rio Ba­glio­ne)


It’s a rare ex­am­ple of “par­a­sitism trans­formed in­to mu­tu­al­ism,” a rela­t­ion­ship where the host spe­cies ben­e­fits from what be­gins as a par­a­sit­ic rela­t­ion­ship, ac­cord­ing to bi­ol­o­gists from the Uni­vers­ity of Neu­châ­tel in France, who par­ti­ci­pated in the work.

In many cuck­oo spe­cies, the new­born cuck­oo al­so kills its nest­mates by push­ing out their eggs before they’re even hatched. 

This does­n’t occur, how­ev­er, with the great spot­ted cuck­oo (Clam­a­tor glan­dar­ius), of south­ern Eu­rope and Af­ri­ca, ac­cord­ing to the au­thors of the new stu­dy. 

They claimed that the cuck­oo, which lays its eggs in the nests of black crows (Cor­vus corone coro­ne), ends up be­ing an “as­set” to the in­fested brood through abil­ity to re­lease an ex­tremely foul-smelling black­ish liq­uid.

Re­search­er Greg­o­ry Röder of Uni­vers­ity of Neuchâ­tel an­a­lyzed the make­up of the ex­cre­tion and found a mix­ture of what he de­scribed as highly caus­tic and re­pul­sive molecules, in­clud­ing bu­tyr­ic ac­id, the char­ac­ter­is­tic smell of vom­it; sul­fur fumes rem­i­nis­cent of de­cay; and oth­er mo­le­cules sug­ges­tive of fe­ces, ran­cid goat meat and rot­ten eggs.

In ex­pe­ri­ments, po­ten­tial nest preda­tors of crows in­variably re­coiled in dis­gust from bits of chick­en tainted with the scent, said the re­search­ers, pub­lish­ing their find­ings in the March 20 is­sue of the jour­nal Sci­ence. The in­ves­ti­ga­tors al­so de­vised an ar­ti­fi­cial mix­ture faith­fully mim­ick­ing the orig­i­nal ex­cre­tion, but with­out its col­or and syr­upy tex­ture, so as to be in­vis­i­ble. This mix­ture, tested with a wide range of preda­tors, con­tin­ued to have its ef­fect, they found.


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Cuckoos are the bird world’s most notorious freeloaders: many lay eggs in the nests of other bird species, leading unwitting parents to raise a little cuckoo while their own young languish or die. But French and Spanish biologists have found one pretty cuckoo species with a helpful side. When threatened, its baby emits a repugnant stench that wards off predators—helping to protect nest-mates in the process. This scent includes molecules that smell like vomit, sulfur, death and feces all rolled into one; predators won’t touch food tainted with it. It’s a rare example of “parasitism transformed into mutualism”—a relationship where the host species benefits from what begins as a parasitic relationship, according to biologists from the University of Neuchâtel in France, who participated in the work. In many cuckoo species, the newborn cuckoo also hatches earlier than its nest mates and pushes their eggs out of the nest, killing their inhabitants. This “murder” doesn’t happen, however, with the great spotted cuckoo (Clamator glandarius), of southern Europe and Africa, according to the authors of the new study. They claimed that the cuckoo, which lays its eggs in the nests of black crows (Corvus corone corone), ends up being an “asset” to the infested brood through ability to release an extremely foul-smelling blackish liquid. Researcher Gregory Röder of University of Neuchâtel analyzed the makeup of the excretion and found a mixture of what he described as highly caustic and repulsive molecules, including butyric acid, the characteristic smell of vomit; sulfur fumes reminiscent of decay; and other molecules suggestive of feces, rancid goat meat and rotten eggs. In experiments, potential nest predators of crows invariably recoiled in disgust from bits of chicken tainted with the scent, said the researchers, publishing their findings in the March 20 issue of the journal Science. The investigators also devised an artificial mixture faithfully mimicking the original excretion, but without its color and syrupy texture, so as to be invisible. This mixture, tested with a wide range of predators, continued to have its effect, they found.