How stress maintains population levels

May 24, 2000

ITHACA, N.Y. -- A continent-wide network of bird-feeding enthusiasts have helped researchers at the Cornell Laboratory of Ornithology prove a long-standing theory that a naturally occurring disease can regulate a wildlife population.

The findings, from a study of mycoplasmal conjunctivitis in house finches (Carpodacus mexicanus) that was published May 2, in Proceedings of the National Academy of Sciences, could give scientists insight into the dynamics of other host/disease systems as well, including an epidemic currently affecting fish in the Chesapeake Bay -- and possibly even AIDS.

"Our data showed that high-density populations of house finches that became infected with mycoplasmal conjunctivitis experienced a dramatic drop in numbers within two to three years after the epidemic began and that they stabilized at about 40 percent of their previous abundance," says co-author André Dhondt, director of Bird Population Studies and professor of ecology and evolutionary biology at Cornell. "At the same time, emerging house finch colonies increased to approximately those same levels, despite the presence of the disease."

Theoretically, says Dhondt, it makes sense that when a disease emerges in a dense population, it moves quickly through that population and wipes out vast numbers because healthy individuals have a higher chance of coming in contact with infected animals. Conversely, healthy animals in lower-density populations are less likely to cross paths with infected individuals, allowing those populations to continue to grow until the disease reaches a density threshold.

This theory, however, had never before been demonstrated because it is extremely difficult to follow the course of a naturally occurring wildlife disease. Scientists need information on host abundance both before, during and after the epidemic sweeps through the population. They also must begin collecting data at the onset of the disease. To do that, symptoms need to be readily detectable and a large network of observers need to be in place. Previously, large-scale studies have focused on diseases that were deliberately introduced as a means to control non-native species.

Cornell ornitholgists were in a unique position when the naturally occurring epidemic began: They could call on the thousands of "citizen scientists" who have been collecting information about their winter feeder birds as part of the ornithology lab's Project FeederWatch since 1988. During the winter of 1993-94, FeederWatchers in the Washington, D.C. area were among the first to observe and report house finches with swollen, crusty eyes. In response, Cornell lab scientists developed a new protocol to help FeederWatchers collect information about the mysterious new disease.

From this evolved the House Finch Disease Survey. "Fortunately, we were in position to act quickly and therefore had an unprecedented opportunity to monitor a wildlife disease from its origin and follow it as it spread," says Laura Kammermeier, project leader for Project FeederWatch. By 1997, participants were reporting diseased house finches throughout most of the species' Eastern range, extending as far as Texas and the Dakotas.

Dhondt and his colleague Wesley Hochachka combined House Finch Disease Survey reports with the National Audubon Society's 100-year-strong Christmas Bird Count database to determine the numbers of affected birds. They estimate that house finch numbers have fallen in the East from some 300 million birds to 180 million. The disease has now stabilized; Dhondt believes that in New England, for example, only about 1 in 20 birds are infected.

Mycoplasmal conjunctivitis is caused by a previously unknown strain of mycoplasmal gallisepticum, a bacterium that typically leads to respiratory infections in domestic poultry. The new strain, which also affects American goldfinches (Carduelis tristis) and a few other wild bird species, causes the eyes of an infected bird to become swollen and crusty. This may lead to blindness and death from starvation as the birds become unable to forage for food.

The disease is spread when healthy birds come into contact with an infected bird or an object touched by a diseased bird. For example, tube feeders require the bird to stick its head into a hole in order to extract seeds. When the eyes of an infected bird come in contact with the opening, the next bird to feed at that perch can pick up the disease. For this reason, feeders should be cleaned with a solution of 1 part bleach to 10 parts water every two weeks or so. Nevertheless, the disease probably spreads most rapidly where the birds sleep together in large, crowded roosts, quite often among populations that do not make regular use of bird feeders.

Dhondt emphasizes that mycoplasmal conjunctivitis cannot be transmitted to humans. And he hopes that more citizen-scientists will join Project FeederWatch to help resolve other scientific questions.
More information on Project FeederWatch, which was developed with grants from the National Science Foundation and is now supported by nominal participation fees to help defray costs of materials, is available by calling tollfree (800) 843-2473 and by visiting the Cornell Laboratory of Ornithology web site: Information also is available by e-mail to or by writing to: Cornell Lab of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850.

Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.

-- PNAS article:

Cornell University

Related Birds Articles from Brightsurf:

In a warming climate, can birds take the heat?
We don't know precisely how hot things will get as climate change marches on, but animals in the tropics may not fare as well as their temperate relatives.

Dull-colored birds don't see the world like colorful birds do
Bengalese finches -- also called the Society finch -- are a species of brown, black and white birds that don't rely on colorful signals when choosing a mate.

Some dinosaurs could fly before they were birds
New research using the most comprehensive study of feathered dinosaurs and early birds has revised the evolutionary relationships of dinosaurs at the origin of birds.

If it's big enough and leafy enough the birds will come
A new study from the Cornell Lab of Ornithology highlights specific features of urban green spaces that support the greatest diversity of bird species.

How do birds understand 'foreign' calls?
New research from Kyoto University show that the coal tit (Periparus ater) can eavesdrop and react to the predatory warning calls of the Japanese tit (Parus minor) and evokes a visual image of the predator in their mind

Microelectronics for birds
Ornithologists and physicists from St Petersburg University have conducted an interdisciplinary study together with colleagues from Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences and the Biological Station Rybachy of the Zoological Institute of the Russian Academy of Sciences.

Birds of a feather better not together
A new study of North American birds from Washington University in St.

Not-so-dirty birds? Not enough evidence to link wild birds to food-borne illness
Despite the perception that wild birds in farm fields can cause food-borne illness, a WSU study has found little evidence linking birds to E. coli, Salmonella and Campylobacter outbreaks.

Birds are shrinking as the climate warms
After 40 years of collecting birds that ran into Chicago buildings, scientists have been able to show that the birds have been shrinking as the climate's warmed up.

Diving birds follow each other when fishing
Diving seabirds watch each other to work out when to dive, new research shows.

Read More: Birds News and Birds Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to