"Long before it's in the papers"
June 04, 2013


Tit-for-tat: birds found to repay wartime help

July 6, 2008
Special to World Science  

When it spots a lurk­ing pred­a­tor, the sparrow-like pied fly­catch­er re­acts in a way com­mon among some birds and mam­mals. It calls up a mob of its peers to drive the in­ter­lop­er away.

But more than a feisty de­fend­er, the northern Eur­o­pe­an bird is al­so a shrewd ac­count keep­er, re­search­ers say: it re­mem­bers which of its neigh­bors an­swered its call to arms, and which stayed home. And it re­pays each in kind. 

The pied fly­catch­er Fi­ce­du­la hy­po­leu­ca (Cour­tesy Mii­ka Silf­ver­berg)

Sci­en­tists say the be­hav­ior of­fers new in­sights in­to the ev­o­lu­tion of coop­era­t­ion and al­tru­ism, and a new ap­precia­t­ion of the com­plex­ity of bird so­cial life. 

Ap­par­ently even some birds have learn­ed that “play­ing nice pays,” Uni­ver­s­ity of Chi­ca­go ev­o­lu­tion­ary bi­olo­g­ist Da­vid Wheatcroft wrote re­cent­ly, al­lud­ing to the fly­catch­er re­search, in which he was not in­volved. 

The find­ings imply “a lev­el of so­phis­tica­t­ion in bird com­mun­i­ties great­er than had pre­vi­ously been real­ized,” he went on, writ­ing in the June 26 ad­vance on­line is­sue of the the re­search jour­nal Trends in Ecol­o­gy & Ev­o­lu­tion. Si­m­i­lar be­hav­ior to the fly­catch­ers’ has been found in red-winged black­birds.

A group at the Uni­ver­s­ity of Dau­gav­pils, Lat­via and the Uni­ver­s­ity of Tar­tu, Es­to­nia placed 300 fly­catch­er cou­ples in nest boxes in groups of three in a pine for­est. 

The re­search­ers then watched what hap­pened when they placed a stuffed owl visibly next to the nests. In cer­tain runs of the ex­pe­ri­ment, the in­ves­ti­ga­tors al­so se­cretly ab­ducted one cou­ple from each group at ran­dom, so that these could­n’t join in any “mob­bing.” 

The re­sults: oth­er birds would in­i­ti­ate mob­bing, by sound­ing spe­cial calls. An hour lat­er, once re­turned to their nest, eve­ry ab­sented bird cou­ple saw its at­tempts to in­i­ti­ate a charge spurned by the pre­vi­ous in­i­ti­a­tor, though oth­er group mem­bers usu­ally still helped. Those who had joined the first time—and all did when avail­able—al­most al­ways saw their as­sis­tance re­paid.

“Co-operating fly­catch­er fam­i­lies won the re­ward,” but “non co-operators were im­me­di­ately pun­ished,” wrote the re­search­ers, In­drikis Krams of the Uni­ver­s­ity of Dau­gav­pils and col­leagues in the Feb­ru­ary is­sue of the jour­nal Be­hav­ior­al Ecol­o­gy and So­cio­bi­o­logy.

Rob­ert Olen­dorf of Mich­i­gan State Uni­ver­s­ity and col­leagues reached si­m­i­lar con­clu­sions in a study with male red-winged black­birds pub­lished in the Jan. 22, 2004 is­sue of Pro­ceed­ings of the Roy­al So­ci­e­ty: Bi­o­log­i­cal Sci­ences. Olen­dorf’s group used recorded bird calls in place of real ones.

The find­ings may help shed light on how coop­era­t­ion evolved, even among un­re­lat­ed in­di­vid­u­als, Krams and col­leagues wrote. That has been a per­en­ni­ally thorny ques­tion. 

Ev­o­lu­tion oc­curs when stronger or fit­ter in­di­vid­u­als in a popula­t­ion re­pro­duce more than oth­ers do, so their genes spread more widely at the ex­pense of less “fit” genes. Many rep­e­ti­tion of this can change spe­cies in­to en­tire­ly new ones. But kind­ness and help­ing seem to pro­vide no fit­ness ad­van­tage, and may even hurt, so it seems any genes for these should have died out long ago. Yet these qual­i­ties ex­ist, and even some pos­si­ble genes for them re­portedly iden­ti­fied.

A range of ex­plana­t­ions has been pro­posed. One the­o­ry is that coop­era­t­ion arises from re­ciprocity: an­i­mals de­vel­op the ten­den­cy to help be­cause they will re­ceive help in re­turn. This poses its own dif­fi­cul­ties—who re­pays the first helper’s trou­ble? Re­gard­less, if re­ciprocity is part of the equa­t­ion, it clearly has a bet­ter chance of evolv­ing among groups of an­i­mals that are fa­mil­iar with each oth­er, so each mem­ber can track who has been naugh­ty and who nice.

Pre­vi­ously, re­ciprocal al­tru­ism had been found only in a a few spe­cies be­sides hu­mans, such as vam­pire bats that ex­change food and some apes. Fly­catch­ers al­so show the abil­ity to rec­og­nize each oth­er as in­di­vid­u­als, Krams and col­leagues wrote—so some birds bat­tles can be added to the list of an­i­mal be­hav­iors ex­plained by re­ciprocal al­tru­ism.

* * *

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When it spots a lurking predator, the sparrow-like pied flycatcher reacts in a way common among some birds and mammals. It calls up a mob of its peers to drive the interloper away. But more than a feisty defender, the flycatcher is also a shrewd account-keeper, researchers say: it remembers which neighbors answered its call to arms, and which stayed home—and repays each in kind. Scientists say the behavior offers new insights into the evolution of cooperation and altruism, and a new appreciation of the complexity of bird social life. Apparently even some birds have learned that “playing nice pays,” University of Chicago evolutionary biologist David Wheatcroft wrote recently, alluding to the flycatcher research, in which he was not involved. The findings imply “a level of sophistication in bird communities greater than had previously been realized,” he went on, writing in the June 26 advance online issue of the the research journal Trends in Ecology & Evolution. Similar behavior to the flycatchers’ has been found in red-winged blackbirds. A group at the University of Daugavpils, Latvia and the University of Tartu, Estonia placed 300 flycatcher couples in nest boxes in groups of three in a pine forest. The researchers then watched what happened when they placed a stuffed owl visibly next to the nests. In certain runs of the experiment, the investigators also secretly abducted one couple from each group at random, so that these couldn’t join in any “mobbing” behavior. The results: Other birds would initiate mobbing, by sounding special calls. An hour later, once returned to their nest, every absented bird couple saw its attempts to initiate a charge shunned by the previous initiator, though other group members usually still helped. Those who had joined the first time—and all did when available—almost all saw their assistance repaid. “Co-operating flycatcher families won the reward,” but “non co-operators were immediately punished,” wrote the researchers, Indrikis Krams of the University of Daugavpils and colleagues in the February issue of the journal Behavioral Ecology and Sociobiology. Robert Olendorf of Michigan State University and colleagues reached similar conclusions in a study with male red-winged blackbirds published in the Jan. 22, 2004 issue of Proceedings of the Royal Society: Biological Sciences. Olendorf’s group used recorded bird calls in place of real ones. The findings may help shed light on how cooperation evolved, even among unrelated individuals, Krams and colleagues wrote. That has been a perennially thorny question for researchers. Evolution occurs when stronger or fitter individuals reproduce more than others in their population, so their genes spread more widely at the expense of less “fit” genes. Many repetition of this can even change species into new ones. But kindness and helping seem to provide no fitness advantage, and may even hurt, so it seems any genes for these should have died out long ago. Yet these qualities exist, and even some possible genes for them reportedly identified. A range of explanations has been proposed. One theory is that the cooperation arises from reciprocity: animals develop the tendency to help because they will receive help in return. This poses its own difficulties—who repays the first helper’s trouble? Regardless, if reciprocity is part of the equation, it clearly has a better chance of evolving among groups of animals that are familiar with each other, so each member can track who has been naughty and who nice. Previously, reciprocal altruism had been shown only in a a few species besides humans, such as vampire bats that exchange food and some apes. Flycatchers also show the ability to recognize each other as individuals, Krams and colleagues wrote—so some birds battles can be added to the list of animal behaviors explained by reciprocal altruism.