Featured Research

from universities, journals, and other organizations

'Mafia' Behavior In Cowbirds? Study First To Document Evidence

Date:
March 7, 2007
Source:
University of Florida
Summary:
Cowbirds have long been known to lay eggs in the nests of other birds, which then raise the cowbirds' young as their own. Now, however, a University of Florida study finds that cowbirds actually ransack and destroy the nests of warblers that don't buy into the ruse and raise their young.

A parasitized Prothonotary Warbler nest (3 cowbird eggs and 5 warbler eggs).
Credit: Image courtesy of Jeff Hoover

"The Sopranos" have some competition -- brown-headed cowbirds.

Cowbirds have long been known to lay eggs in the nests of other birds, which then raise the cowbirds' young as their own.

Sneaky, perhaps, but not Scarface.

Now, however, a University of Florida study finds that cowbirds actually ransack and destroy the nests of warblers that don't buy into the ruse and raise their young.

Jeff Hoover, an avian ecologist at the Florida Museum of Natural History, is the lead author on the first study to document experimental evidence of this peeper payback -- retaliation to encourage acceptance of parasitic eggs.

Findings will be published online in the Proceedings of the National Academy of Sciences March 5.

"It's the female cowbirds who are running the mafia racket at our study site," said Hoover, who has a joint appointment with the Illinois Natural History Survey. "Our study shows many of them returned and ransacked the nest when we removed the parasitic egg."

So-called "brood parasitic birds" lay eggs in the nests of host birds that raise the parasite's offspring, usually at the expense of some of their own. The brown-headed cowbird parasitizes more than 100 host species, including many Neotropical migratory birds such as warblers, tanagers and vireos. Prothonotary warblers were used for this study because they almost always accept cowbird eggs, Hoover said.

Hosts that use their beaks to grasp or puncture parasitic eggs and remove them from the nest are called "ejecters." "Accepter" hosts raise parasitic eggs.

"Retaliatory mafia behavior in cowbirds makes hosts' acceptance of cowbird eggs a better proposition than ejection," Hoover said. "The accepting warblers in our study produced more of their own offspring, on average, than those where we ejected cowbird eggs."

Hosts may lose some, but not all, of their biological offspring by accepting parasitism. The retaliatory behavior of ransacking nests encourages warblers to raise the cowbirds' offspring.

"We wanted to determine if the cowbirds were responsible for nest predation after we removed cowbird eggs from parasitized warbler nests," Hoover said. To test for this, Hoover collaborated with Scott Robinson, Florida Museum Ordway eminent scholar and natural history chair, to manipulate cowbird access to warbler nests in the Cache River watershed of southern Illinois. The researchers monitored 182 predator-proofed nests over four breeding seasons.

Hoover and Robinson found that warbler nests were ransacked 56 percent of the time when researchers experimentally removed the parasitic eggs and cowbirds were allowed nest access, versus only 6 percent when the cowbird eggs were accepted and cowbirds had nest access. No nests were ransacked when researchers removed cowbird eggs and cowbirds were denied nest access. Together, these results implicate cowbirds and provide evidence of mafia behavior.

"We also found evidence for 'farming' behavior," Hoover said. "Cowbirds 'farm' a non-parasitized nest by destroying its contents so that the host will build another. The cowbird then syncs its egg laying with the hosts' 'renest' attempt."

Hoover found that warbler nests that were never parasitized but that cowbirds had access to, were ransacked 20 percent of the time. "Cowbirds parasitized 85 percent of the renests, which is strong supporting evidence for both farming and mafia behavior," he said.

Hoover and Robinson's results imply that cowbirds actively monitor nests they parasitize -- which supports the idea that cowbirds continue to visit nests they have parasitized to see the results of their handiwork.

Stephen Rothstein, a zoology professor at the University of California in Santa Barbara, said other studies have shown evidence contrary to mafia and farming behaviors.

"Video surveillance would show the proportion of nest predation attributable to cowbirds," Rothstein said. "The phenomenon may be perfectly true for these warblers, but that doesn't mean it holds true for other species, especially those that aren't nesting in special circumstances. Nevertheless, this new study may extend our knowledge of the extent to which parasitic cowbirds may have evolved tactics to facilitate their parasitism."

Hoover said his future research includes video surveillance of individually banded female cowbirds and warbler nests.


Story Source:

The above story is based on materials provided by University of Florida. Note: Materials may be edited for content and length.


Cite This Page:

University of Florida. "'Mafia' Behavior In Cowbirds? Study First To Document Evidence." ScienceDaily. ScienceDaily, 7 March 2007. <www.sciencedaily.com/releases/2007/03/070305202649.htm>.
University of Florida. (2007, March 7). 'Mafia' Behavior In Cowbirds? Study First To Document Evidence. ScienceDaily. Retrieved September 2, 2014 from www.sciencedaily.com/releases/2007/03/070305202649.htm
University of Florida. "'Mafia' Behavior In Cowbirds? Study First To Document Evidence." ScienceDaily. www.sciencedaily.com/releases/2007/03/070305202649.htm (accessed September 2, 2014).

Share This




More Plants & Animals News

Tuesday, September 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Sharks Off the Menu and on the Tourist Trail in Palau

Sharks Off the Menu and on the Tourist Trail in Palau

AFP (Sep. 2, 2014) Tourists in Palau clamour to dive with sharks thanks to a pioneering conservation initiative -- as the island nation plans to completely ban commercial fishing in its vast ocean territory. 01:15 Video provided by AFP
Powered by NewsLook.com
We've Got Mites Living In Our Faces And So Do You

We've Got Mites Living In Our Faces And So Do You

Newsy (Aug. 30, 2014) A new study suggests 100 percent of adult humans (those over 18 years of age) have Demodex mites living in their faces. Video provided by Newsy
Powered by NewsLook.com
Washington Wildlife Center Goes Nuts Over Baby Squirrels

Washington Wildlife Center Goes Nuts Over Baby Squirrels

Reuters - US Online Video (Aug. 30, 2014) An animal rescue in Washington state receives an influx of orphaned squirrels, keeping workers busy as they nurse them back to health. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Experimental Ebola Drug ZMapp Cures Lab Monkeys Of Disease

Experimental Ebola Drug ZMapp Cures Lab Monkeys Of Disease

Newsy (Aug. 29, 2014) In a new study, a promising experimental treatment for Ebola managed to cure a group of infected macaque monkeys. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins