a

"Long before it's in the papers"
January 20, 2011

RETURN TO THE WORLD SCIENCE HOME PAGE

Birds’ plastic nest décor carries a message, scientists find

Jan. 20, 2011
Courtesy of Science
and World Science staff

Mem­bers of a bird spe­cies that dec­o­rate their nests with bits of white plas­tic do it for more than just looks, new re­search sug­gests.

Sci­en­tists stu­dy­ing black kites—medium-sized birds of prey—found that the adorn­ments al­so car­ry a mes­sage. The birds that use the most white plas­tic are ap­par­ently al­so the best fight­ers, pro­duce the most chicks and live in the best ter­ri­to­ries.

A decorated nest of an 11-year-old black kite, an age at which the kites are at peak re­prod­uct­ive per­form­ance and typ­i­cally de­cor­ate ex­u­ber­antly. (Cou­rtesy F. Se­rgio)

About 20 days be­fore lay­ing their eggs, male and female black kites usu­ally beg­in scav­eng­ing their sur­round­ings for items to dec­o­rate their nests with. These are most of­ten bits of white plas­tic, such as scraps of bags.

A group of re­search­ers led by Fab­rizio Ser­gio and Ju­lio Das at the Su­pe­ri­or Coun­cil for Sci­en­tif­ic In­ves­ti­ga­t­ion in Se­ville, Spain, mon­i­tored 127 black kite nests in Doñana Na­tional Park in Spain. They found that the strongest birds, who were sev­en to 12 years old, dec­o­rated their nests co­pi­ous­ly, but very young and eld­erly birds hardly did so at all.

The in­ves­ti­ga­tors al­so found that black kites with the most white plas­tic in their nests were al­so the most ca­pa­ble of de­fend­ing their ter­ri­to­ry from oth­er, in­trud­ing black kites. And it does­n’t seem like the birds are in­ter­est­ed in pre­tend­ing to be some­thing they are not: When the re­search­ers added ex­tra plas­tic to the birds’ nests, most of them re­moved it im­me­di­ate­ly.

The sci­en­tists sug­gest the birds don’t want to pre­tend to be tough if they really aren’t—much like a new stu­dent in a ka­ra­te class would­n’t want to pre­tend to be a black belt on the first day. 

The find­ings sug­gest struc­tures built by an­i­mals might serve as sig­nal­ing de­vices more of­ten than was pre­vi­ously thought, Ser­gio and col­leagues ar­gue. 

By dec­o­rat­ing their nests abun­dant­ly, it seems, strong black kites gain the ben­e­fit of hav­ing po­ten­tial com­peti­tors pass them over for at­tack, the re­search­ers said. On the oth­er hand, it would seem the bird­s—who are giv­en to rough com­pe­ti­tion and in­tru­sion in­to each oth­er’s ter­ri­to­ries—aren’t too dumb to spot peers that are bla­tantly fak­ing. The ex­pe­ri­ments’ re­sults in­di­cate that pairs that “sud­denly ad­ver­tise a high-qual­ity ter­ri­to­ry” may open them­selves up to at­tack, the sci­en­tists wrote, re­port­ing their re­sults in the Jan. 21 is­sue of the re­search jour­nal Sci­ence.

The white plas­tic de­cora­t­ion be­hav­ior is com­mon among black kites at least across Eu­rope, Ser­gio said; mem­bers of the spe­cies al­so in­hab­it Af­ri­ca, Asia and Aus­tral­ia. It’s un­clear when or how the nest-dec­o­rat­ing be­gan, or wheth­er it is a ge­net­ic or “cul­tur­al” phe­nom­e­non, Ser­gio added. Ob­serva­t­ions of the birds us­ing human-made ob­jects in their nests date back to the early 1800s, he ex­plained, but “it was not [un­til] up to 5 years ago that we started to in­ves­t­i­gate the phe­nom­e­non in­ten­sive­ly.”

* * *

Send us a comment on this story, or send it to a friend

 

Sign up for
e-newsletter
    
 
subscribe
 cancel

On Home Page         

LATEST

  • B­irds’ plas­tic nest dé­cor car­ries a mes­sage

  • Ran­ge of aster­oid types could have seed­ed life, study finds

EXCLUSIVES

  • From bra­in sci­ence, new ques­tions about fr­ee wi­ll

  • Scien­tists ex­plore whe­ther some ap­es shake he­ads for "no"

  • It se­ems we're all more hu­man than aver­age

  • Ba­by temper­ament found to pre­dict ad­ult bra­in struc­ture

MORE NEWS

  • What hit the Mo­on? New cra­ter makes a spl­ash

  • T­racks may tell tale of rep­tilian land con­quest

  • Plan­ets found shar­ing strange dan­ces

  • Newfound sta­rs seen sha­ttering known si­ze lim­its

Members of a bird species that decorate their nests with white plastic objects do it for more than just looks, new research suggests. Scientists studying black kites—medium-sized birds of prey—found that the adornments also carry a message. The birds that use the most white plastic are apparently also the best fighters, produce the most chicks and live in the best territories. About 20 days before laying their eggs, male and female black kites usually begin scavenging their surroundings for items to decorate their nests with, most often bits of white plastic. A group of researchers led by Fabrizio Sergio and Julio Das at the Superior Council for Scientific Investigation in Seville, Spain, monitored 127 black kite nests in Doñana National Park in Spain. They found that the strongest birds, who were seven to 12 years old, decorated their nests copiously, but very young and elderly birds hardly did so at all. The investigators also found that black kites with the most white plastic in their nests were also the most capable of defending their territory from other, intruding black kites. And it doesn’t seem like the birds are interested in pretending to be something they are not: When the researchers added extra plastic to the birds’ nests, most of them removed it immediately. The scientists suggest the birds don’t want to pretend to be tough if they really aren’t—much like a new student in a karate class wouldn’t want to pretend to be a black belt on the first day. The findings suggest structures built by animals might serve as signaling devices more often than was previously thought, Sergio and colleagues argued. By decorating their nests abundantly, it seems, strong black kites gain the benefit of having potential competitors pass them over for attack, the researchers said. On the other hand, it would seem the birds—who are given to rough competition and intrusion into each other’s territories—aren’t too dumb to figure out which of their peers are blatantly faking. The experiments’ results indicate that pairs that “suddenly advertise a high-quality territory” may open themselves up to attack, the scientists wrote, reporting their results in the Jan. 21 issue of the research journal Science. The white plastic decoration behavior is common among black kites at least across Europe, Sergio said; members of the sepcies also inhabit Africa, Asia and Australia. It’s unclear when or how the nest-decorating began, or whether it is a genetic or “cultural” phenomenon, Sergio added. Observations of the birds using human-made objects in their nests date back to the early 1800s, he explained, but “it was not [until] up to 5 years ago that we started to investigate the phenomenon intensively.”