When Rick Ostfeld heard about the sky-darkening flocks of birds descending this winter on Hopkinsville, Ky., he couldn't help but think of Alfred Hitchcock's "The Birds."
"I remember watching it multiple times as a kid, just to scare myself," said Ostfeld, a disease ecologist with the Cary Institute of Ecosystem Studies in Millbrook, N.Y.
California's Bodega Bay, where Hitchcock set his horror flick, also happens to be where Ostfeld toiled on his doctoral thesis. Still, what struck him most about the latest news was the familiar nonfiction storyline from his years of studying the ecology of infectious disease: A congregation of millions of blackbirds and European starlings -- possibly influenced by climate change and a human-altered landscape -- is coating neighborhoods in white excrement and may be increasing the risk of disease for people and pets.
The disease du jour is a fungal infection called histoplasmosis. The pneumonia-like illness can be deadly to dogs, and also serious for humans if left untreated, according to the U.S. Centers for Disease Control and Prevention.
"We're disturbing the environment, and that could be creating the perfect storm," said Ostfeld.
He has known other biologists who fell ill from histoplasmosis while researching in bat caves. In his own research, Ostfeld has found that the risk of Lyme disease rises when biodiversity drops due to human activities. He is now investigating the potential role of climate change on that disease's spread. And this past October, Ostfeld discussed with The Huffington Post the potential for city rats flooded from their underground residences by Hurricane Sandy to begin infesting more human homes and businesses, possible raising the human risk of infectious diseases carried by the rodents, such as leptospirosis, hantavirus, typhus, salmonella and even the plague.
Climate scientists have suggested that global warming could be increasing the threat of extreme storms like Sandy, and reports are now coming in that rat populations are escalating in some Sandy-struck neighborhoods.
The New York City Department of Health told The Huffington Post in a statement that rat reports are actually down citywide after the storm compared to the previous year. City council officials, however, are pushing for more money to bait, kill and remove rats, reported The New York Times, which points out that areas along the hard-hit shorelines -- such as Manhattan's Lower East Side and Brooklyn's Greenpoint -- have seen an uptick in complaints.
Ostfeld remains concerned about possible implications for public health. Leptospirosis, he said, is similar to the flu and might "easily be undetected and unreported."
As for the birds down South, recent studies suggest that increasing temperatures and altered precipitation patterns could change migratory patterns. Frank La Sorte, a researcher at the Cornell Lab of Ornithology, noted that with changing climate conditions, more food is becoming available farther north during the winter, and that could be causing some birds to stop early in their annual southward journey.
"As these species roam around looking for food, they increasingly test the northern limit -- especially if they're not tied to a specific resource or habitat," La Sorte said. "That could be at play here. But it's hard to say any specific cause unless you study a particular event in detail."
As with proving that climate change is connected to a singular weather event, linking it to the movement of wildlife is extremely difficult. For one, this is not the first winter that Hopkinsville has seen millions of birds take up residence.
"That area is notorious for blackbirds," said Norman Goodman, a microbiologist and emeritus professor at the University of Kentucky, who recalled increased cases of histoplasmosis with massive roosts in years past. "At one time, we had about 5 million blackbirds in a pine grove at Fort Campbell."
As Goodman explained, the birds' feces act as good fertilizer for histoplasmosis spores that naturally live for years in the soil. If the fertilized dirt is then disturbed, those spores can become airborne and infect the lungs of people and pets. However, he emphasized that the mere presence of the birds -- even their droppings-- doesn't mean people will get sick.
Dr. Wade Northington, director of the Murray State University Breathitt Veterinary Center, an animal disease diagnostic facility that covers Hopkinsville, added that birds and bats can also pick up the fungus off the ground. While the animal won't show symptoms, its intestinal tract can play host to multiplying histoplasmosis spores, which the animal then deposits elsewhere as it flies about.
"The area where these birds have been roosting will be a problem," said Northington, who noted he hadn't seen flocks this large for at least 15 years. "People need to be very, very careful."
The best idea, according to Goodman and Northington, is to leave soiled soils alone.
Raina Plowright, a researcher at the Center for Infectious Disease Dynamics at Penn State University, sees a parallel between the Kentucky birds and her work on Australian fruit bats.
"Bats rely on nectar and fruit, and generally have to move great distances to always find it. But they discovered that urban food sources are there year-round," Plowright said. "This could be a factor in the increasing number of deadly Hendra virus outbreaks in Australia."
Hendra is known to infect horses, likely from the urine of infected bats. Horses can then transmit the virus to people.
Plowright added that climate change may well be playing a role in Hendra, too, but just what role remains unclear. "There does seem to have been some links between environmental perturbations and Hendra outbreaks," she said, emphasizing the complexity of teasing apart the factors in the spread of disease.
In addition to the Hitchcock classic, the swarms of birds in Kentucky also reminded Ostfeld of the final scene in the more recent Hollywood film "Contagion." The 20-second sequence of clips acts as a prequel to the nightmare scenario played out in the movie: A bulldozer clears a patch of trees for a new piggery, into which a displaced and diseased bat drops a chunk of banana, which is gobbled by a pig that later lands in the hands of a chef.
As the film illustrates, and as HuffPost has reported in "The Infection Loop," wild flocks of animals don't always just bring along familiar diseases. Three-quarters of new, emerging or re-emerging human diseases originate in animals.
"You've got these mobile creatures harboring pathogens that get disturbed in various ways by human activities, which are then brought into close proximity to humans," said Ostfeld. "These are common themes that might suggest a general pattern, and something that may continue to happen."