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January 18, 2011

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Birds may attract mates with “scary movie” effect

Jan. 18, 2011
Courtesy of University of Chicago Medical Center
and World Science staff

Us­ing a hor­ror film to br­ing your date clos­er is a clas­sic move in the teen­age play­book. Now, a study of Aus­tral­ian birds finds that oth­er an­i­mals may use the same “scary mov­ie ef­fect” to at­tract fe­male at­ten­tion, by pig­gy­back­ing their mat­ing song on­to the calls of preda­tors.

Male splen­did fairy-wrens, small birds from Aus­tral­ia, sing a spe­cial song each time they hear the call of one of their preda­tors, the butcher­birds. New re­search has found that this seem­ingly dan­ger­ous be­hav­ior may ac­tu­ally serve as a call to po­ten­tial mates – a flirta­t­ion us­ing fear.

A pair of splen­did fairy-wrens on their ter­ri­tory in South Aus­tra­lia. (Cred­it: Mitch­ell Wal­ters/U. Chi­ca­go)

“Fe­males do, in fact, be­come espe­cially at­ten­tive af­ter hear­ing butch­er­bird calls,” said Em­ma Greig of Cor­nell Uni­vers­ity at Ith­a­ca, N.Y., one of the re­search­ers. “It seems that male fairy-wrens may be sing­ing when they know they will have an at­ten­tive au­di­ence, and, based on the re­sponse of fe­ma­les, this strat­e­gy may ac­tu­ally work!”

Pub­lished in the re­search jour­nal Be­hav­ior­al Ecol­o­gy, the study in­volved play­ing sound clips to splen­did fairy wrens at a con­serva­t­ion cen­ter in South­ern Aus­tral­ia.

Af­ter years of stu­dying these birds and their close rel­a­tives, the su­perb fairy-wrens, re­search­ers had no­ticed the un­ique, con­sist­ent pair­ing of butch­er­bird calls with a un­ique call known as Type II song. “The male be­gins his Type II call im­me­di­ately af­ter the butch­er­bird be­gins to call, so they’re bas­ic­ally right on top of each oth­er,” said Uni­vers­ity of Chi­ca­go re­searcher Ste­phen Pruett-Jones, a mem­ber. “It sounds like a duet.”

But the­o­ries var­ied as to why fairy-wrens would risk at­tracting a pred­a­tor by sing­ing. Was it an alarm call to oth­er fairy-wrens in the ar­e­a? A dis­play of their brav­ery and phys­i­cal fit­ness to at­tract mates? Or an ef­fec­tive means of cap­tur­ing the at­ten­tion of any fe­males around?

Greig played dif­fer­ent com­bina­t­ions of songs from her iPod to male and fe­male fairy-wrens in their nat­u­ral hab­i­tat: the ter­ri­to­rial Type I song, as well as the Type II song with and with­out the pre­ced­ing pred­a­tor call. The ex­pe­ri­ments found that fe­males were most at­ten­tive – as meas­ured by look­ing in the di­rec­tion of the call and re­spond­ing with their own song – when the butch­er­bird-preceded Type II song was played.

“The most ex­cit­ing pos­si­bil­ity is that Type II songs have a sex­u­al func­tion, and that fe­males are more easily stim­u­lat­ed by, or re­cep­tive to, dis­plays af­ter be­ing alerted by a pred­a­tor, such that the ma­le’s song is espe­cially at­trac­tive,” Greig said.

The re­sults sug­gest that males use the pred­a­tor call as an “alert­ing sig­nal,” Pruett-Jones said, si­m­i­lar to how hu­mans might cap­ture anoth­er per­son’s at­ten­tion by start­ing their sen­tence with “Hey!” For the fe­ma­les, the sig­nal may car­ry in­forma­t­ion about the loca­t­ion of po­ten­tial mates in neigh­bor­ing ter­ri­to­ries, and po­ten­tially may nudge them to­wards mat­ing, Greig said.

Splen­did fairy-wrens are in­ter­est­ing to sci­en­tists stu­dying ev­o­lu­tion and mat­ing pat­terns due to their un­ique so­cial struc­ture, said Pruett-Jones. While the birds are so­cially mo­nog­a­mous, form­ing ma­le-fe­male pairs that last their en­tire lives, they are sex­u­ally pro­mis­cu­ous, mat­ing pre­dom­i­nantly with birds out­side of their home pair.

On­go­ing re­search is meas­ur­ing the phys­i­cal at­tributes and ge­net­ics of male splen­did fairy-wrens and their off­spring to see if there is a con­nec­tion be­tween Type II sing­ing and mat­ing suc­cess. So far, no link has been found be­tween the be­hav­ior and phys­i­cal health, the in­ves­ti­ga­tors said, sug­gesting Type II songs aren’t a self-imposed hand­i­cap to make males look more fit and at­trac­tive to fe­ma­les.

All males “gave Type II songs with equal fre­quen­cy, which sug­gests that sing­ing af­ter a pred­a­tor vo­cal­izes may not be as costly a be­hav­ior as you might imag­ine,” Greig said. “Con­trary to what you might ex­pect, sing­ing af­ter a pred­a­tor call may ac­tu­ally be quite safe: the male fairy-wrens know where the pred­a­tor is, and he al­so knows that the pred­a­tor is­n’t ac­tively hunt­ing at that mo­ment, but is in­stead sing­ing its heart out.”

Greig is al­so cur­rently test­ing how com­mon the “scary mov­ie ef­fect” is be­yond the splen­did and su­perb fairy-wrens. While only two oth­er birds, fairy gery­gones and white-throated mag­pie jays, are thought to dem­on­strate si­m­i­lar pred­a­tor-elicited dis­play, the re­search­ers be­lieve it may be pre­s­ent and un­de­tected in oth­er spe­cies as well.

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Using a horror film to bring your date closer is a classic move in the teenage playbook. Now, a study of Australian birds finds that other animals may use the same “scary movie effect” to attract female attention, by piggybacking their mating song onto the calls of predators. Male splendid fairy-wrens, a small bird from Australia, sing a special song each time they hear the call of one of their predators, the butcherbirds. New research has found that this seemingly dangerous behavior may actually serve as a call to potential mates – a flirtation using fear. “Females do, in fact, become especially attentive after hearing butcherbird calls,” said Emma Greig, a postdoctoral researcher at Cornell University at Ithaca, N.Y., and one of the researchers. “It seems that male fairy-wrens may be singing when they know they will have an attentive audience, and, based on the response of females, this strategy may actually work!” Published in the research journal Behavioral Ecology, the study involved playing sound clips to splendid fairy wrens at a conservation center in Southern Australia. After years of studying these birds and their close relatives, the superb fairy-wrens, researchers had noticed the unique, consistent pairing of butcherbird calls with a unique call known as Type II song. “The male begins his Type II call immediately after the butcherbird begins to call, so they’re basically right on top of each other,” said University of Chicago researcher Stephen Pruett-Jones, a member. “It sounds like a duet.” But theories varied as to why fairy-wrens would risk attracting a predator by singing. Was it an alarm call to other fairy-wrens in the area? A display of their bravery and physical fitness to attract mates? Or an effective means of capturing the attention of any females around? Greig played different combinations of songs from her iPod to male and female fairy-wrens in their natural habitat: the territorial Type I song, as well as the Type II song with and without the preceding predator call. The experiments found that females were most attentive – as measured by looking in the direction of the call and responding with their own song – when the butcherbird-preceded Type II song was played. “The most exciting possibility is that Type II songs have a sexual function, and that females are more easily stimulated by, or receptive to, displays after being alerted by a predator, such that the male’s song is especially attractive,” Greig said. The results suggest that males use the predator call as an “alerting signal,” Pruett-Jones said, similar to how humans might capture another person’s attention by starting their sentence with “Hey!” For the females, the signal may carry information about the location of potential mates in neighboring territories, and potentially may nudge them towards mating, Greig said. Splendid fairy-wrens are interesting to scientists studying evolution and mating patterns due to their unique social structure, said Pruett-Jones. While the birds are socially monogamous, forming male-female pairs that last their entire lives, they are sexually promiscuous, mating predominantly with birds outside of their home pair. Ongoing research is measuring the physical attributes and genetics of male splendid fairy-wrens and their offspring to see if there is a connection between Type II singing and mating success. So far, no link has been found between the behavior and physical health, the investigators said, suggesting Type II songs aren’t a self-imposed handicap to make males look more fit and attractive to females. All males “gave Type II songs with equal frequency, which suggests that singing after a predator vocalizes may not be as costly a behavior as you might imagine,” Greig said. “Contrary to what you might expect, singing after a predator call may actually be quite safe: the male fairy-wrens know where the predator is, and he also knows that the predator isn’t actively hunting at that moment, but is instead singing its heart out.” Greig is also currently testing how common the “scary movie effect” is beyond the splendid and superb fairy-wrens. While only two other birds, fairy gerygones and white-throated magpie jays, are thought to demonstrate similar predator-elicited display, the researchers believe it may be present and undetected in other species as well.