With the heat on, birds show confused behavior
The Mississippi River was particularly beautiful for this time of year, thought Mindy Blank, 16, as she traveled through southeastern Minnesota on her way back home to Winona.
The sun beat down on the brown grass of the riverbanks, the rays falling from a sapphire sky onto the still, steel waters. A bitter cold hung heavily in the air, and thick sheets of ice floated down the middle of the river.
But one unexpected element made the scene even more striking, and, in a way, worrying.
“I saw tens of thousands of geese,” said Mindy, an environmental enthusiast, “just sitting in the fields."
Under ordinary circumstances, the presence of so many birds might have impressed her, but Mindy witnessed this unusual spectacle in the middle of January, a cold month anywhere and an especially brutal one in Minnesota.
“The geese [in Minnesota] usually migrate south in November,” Mindy said.
Her experience is the latest report of abnormal bird behavior throughout the world.
Just a week earlier, hundreds of birds fell dead in the streets and fields around Austin, Texas. Migratory birds have been dropping dead up and down the western coast of Australia for the better part of a year.
And numerous species are showing up where they never have before, or they aren’t leaving locations that they have always left in winter.
While research proving a definite link between the mass bird deaths and global warming doesn’t exist yet, scientists say there is no mistake about it: Man-made emissions are making conditions worse for birds.
That climate change-related trouble abounds is no secret. Al Gore’s Oscar-winning film, “An Inconvenient Truth," demonstrated the effects that climate change could have on birds and other species. And the U.S. Senate Committee on Environment and Public Works held a subcommittee hearing on global warming and wildlife in early February to review the warming environment’s effects on amphibians and birds.
Warmer climates throughout the United State have compromised birds’ migratory sensors, said Roger Lederer, a retired professor of ornithology and ecology. Some migrate earlier than they should and travel farther north, where they often can’t survive, and others don’t migrate south at all, leaving them susceptible to cold spells.
Over the past 400,000 years, carbon dioxide emissions from the earth and the earth’s temperature have fluctuated together, according to the Environmental Protection Agency, with both rising to unprecedented levels in just the last 50 years.
The warmer temperatures have allowed some birds, like geese and mourning doves, which normally migrate south for the winter, to stay in their summertime habitats.
Others that did migrate are now returning north prematurely. The arrival dates of 20 species of migratory birds in North America were up to 21 days earlier in 1994 than in 1965, according to a report by the American Bird Conservancy.
“Who knows whether they’ll adapt or not,” Lederer said. “Global warming is happening at a much faster rate than it has in the past.”
But birds, like humans, are complicated creatures. They don’t rely only on temperature to migrate. Other factors, like food sources, which are directly affected by warmer temperatures, and the length of days, are just as important.
In fact, migrating birds have always depended primarily upon day length, which is a better indicator of consistently warmer weather for birds.
“Takeoff [for migration] is associated with the photoperiod,” Lederer said, using the term for day-length. “As the day lengthens, they go north and as the day shortens they go south.”
But food sources are appearing earlier, because the soil is warmer, which draws birds out of that pattern and allows them to travel north prematurely. And in many cases, Lederer said, birds are traveling farther north than they normally would, or should, which exposes them to spring snowstorms.
Climate change also affects even those birds that have maintained their basic patterns.
“If the species expects to get up north, it expects certain conditions," said Steve Holmer, spokesman for the American Bird Conservancy (ABC). “They might get up north later [than birds that came early] and food sources might be gone or past their peak.”
And as birds live farther north for longer periods of time, more people put out bird feeders, attracting more birds and pushing forward a cycle that ultimately harms the Earth’s feathered friends.
It is less clear, though, that these factors are directly causing more bird deaths. Bird mortality has increased over the past few years, especially among waterfowl, according to U.S. Fish and Wildlife Service statistics.
But scientists say a variety of issues, from habitat destruction to disease, may all be possible causes. And climate change likely influences them all. Birds may be getting sicker as it gets warmer.
“[Bird deaths] may be an indirect effect of a warmer environment that disease can stick around for a longer time,” said John Marzluff, a wildlife science professor at the University of Washington-Seattle. Warmer temperatures could result in a quicker spread of malaria and bird flu.
Lederer and Marzluff also point to habitat destruction and changing ecosystems as culprits.
Lederer said the tropics are disappearing at a fast rate because of the effects of increased human density, and Marzluff predicts climate change will create unanticipated changes for certain ecosystems and the birds within them.
“Novel species will come into the habitat more easily because of climate change,” said Marzluff, causing forests to be “riddled with all sorts of things that destroy the habitat.”
At risk are migratory species like the cerulean warbler, whose numbers are declining at about 3 percent a year, Holmer said.
“Since the 1960s, there’s been about an 80 percent reduction in [the warbler’s] population,” he said. “They need large blocks of interior forest, and there is less of that available.”
Evolution might help limit many of the most disastrous ornithological consequences of climate change.
“Mourning doves and geese throughout the Midwest are wintering farther north and not migrating,” Marzluff said, “but chances are, a few of them are going to be able to handle it and those attributes will be passed on through natural selection and enable the population to adapt.”
And for the rest of the birds? For now, just call it an extended vacation up north.
“Desert Southwest birds, like the white-eared hummingbird, which is usually just an Arizona-New Mexico bird, is showing up in Michigan,” said Dan Casey, an ABC conservationist. “When that shows up in Michigan, it makes one wonder.”