Birds just know when winter storm is coming
Today we continue our annual look at what makes this season special, a time when nature is doing much more than just going to sleep for three months. Welcome to the Science of Winter.
TOM SPEARS
OTTAWA Birds know hours in advance when a winter storm is rolling in — information they use to make vital choices about feeding, hiding or flying to safety.
Many birds appear to have an internal barometer, say scientists at Western University in London. They sense slight changes in air pressure, and they can also detect a dip in temperature when a cold front is coming.
The mechanism is a mystery, said Scott Macdougall-shackleton of Western’s Advanced Facility for Avian Research. “We don’t know how. There are a number of hypotheses but we don’t know for sure yet.”
His facility houses the world’s first hypobaric climatic wind tunnel for bird flight. Turning the air pressure up and down allows research into the physiology and aerodynamics of bird flight at different altitudes.
“We know that birds and other animals can detect subtle changes in air temperature. Many birds somehow sense that very minute drop in air pressure that typically signals low pressure coming,” along with a storm, Macdougall-shackleton said.
Birds have two options, he said: “That depends on the bird. They either want to get out of there, or they want to hunker down.
“We’ve done a lot of work on various sparrow species that forage on the ground. If you’re a sparrow in winter and a storm is coming, that probably means there is going to be snow. Sparrows need to eat while they can.
“When we expose these sparrows to a drop in air pressure they start eating more,” storing energy. He likens it to the people of his former home in Baltimore who would stock up at the supermarket whenever a major winter storm was set to roll in.
Similarly, when the lab simulated high pressure and cold weather associated with winds out of the north in the spring, the birds decreased their northbound migratory flight behaviour.
Some birds in southeastern states evolved a trick of dodging storms that approach from the west. They fly south out of the storm’s path, then west, then come back up behind the storm.
“A large number of animals are probably detecting these subtle changes in barometric pressure,” he said.
Behaviour changes have even been measured in sharks.
“How sharks are sensing that under water is a total mystery.”
Birds may also react to infrasound, or sound at a frequency too low for humans to hear. Low-frequency sound travels a long way and one theory is that birds are hearing far-off rumbles from thunder “probably many hours in advance.”
Climate theory predicts that a warming world will bring more storms, and Macdougall-shackleton wants to know how this affects birds and other wildlife.
“I’m interested in understanding in what situations they can cope, and in what situations they will not be able to cope,” he said.
“If those extreme events become more common, I think it’s useful to understand how animals predict and cope with them.
“Birds are important not only for the ecosystem but they are culturally important to us. Really, I’m just motivated in trying to understand how they are coping with the changing environment,” he added.