High-Tech 'Backpacks' Reveal the Secrets of Snowy Owls

In November 2013, birders started noticing something unusual. Snowy owls — the majestic birds with 5-foot wingspans that typically spend their lives in the Arctic — were appearing farther south than normal.

By December, the owls — the same species as Harry Potter's letter-carrying pet, Hedwig — had been spotted as far south as Florida and Bermuda.

The migration of snowy owls southward is called an irruption, and every four years there's one timed with lemming cycles. But in the winter of 2013/2014, the irruption broke records and raised many questions about the species.

"We realized that in many respects, we know more about the ecology of these birds on their breeding grounds in the Arctic than we do about their lives when they're down here with us," said naturalist Scott Weidensaul.

The irruption inspired him to co-found Project SNOWstorm, a crowd-sourced initiative that studies snowy owl irruptions so the species can be better understood and conserved.

Volunteers started a website and launched a crowd-funding campaign with a goal of raising $20,000 to pay for equipment. In a matter of weeks, they'd raised nearly double their target amount.

There are numerous facets to SNOWstorm. Birders upload photos of the owls to determine the distribution of age and sex, while scientists analyze blood and feather samples as well as perform necropsies on owls killed in accidents or found dead.

But Weidensaul says the most exciting part of the project has been tagging snowy owls with GPS/GSM transmitters so scientists — and the rest of us — can follow their movements.

How do you tag an owl?

(tagged owl) Scott Weidensaul/Project SNOWstorm

A transmitter weighs 45 grams — about as much as seven U.S. quarters — and it's attached to an owl's back via a backpack harness made of woven Teflon ribbon.

Each harness is individually fitted so it sits high in the middle of the owl's back, at its center of gravity. It's made to stay on for life and doesn't restrict flight. The design has been used for decades on many birds of prey and doesn't have an effect on the birds' survival.

Before tagging an owl, researchers first weigh the bird and check its breast muscle and subcutaneous fat deposits.

"We won't tag an owl if the unit would weigh more than 2-3 percent of the owl's body weight, a limit that's been shown in past studies to be safe," said Weidensaul.

The solar-powered transmitters record latitude, longitude and altitude 24 hours a day, and unlike traditional transmitters, they use the cellular phone network to send information. When the owl is out of range of a cell tower, the transmitters store up to 100,000 locations to be shared when the bird flies back in range.

Last winter, SNOWstorm tagged 22 snowy owls, and they recently tagged this winter's first owl, a female named Delaware, pictured above, who was injured at a Maryland airport last year. Delaware spent the summer in rehab and was released in early December.

What have we learned?

Until recently, little was known about the winter behavior of snowy owls, especially after dark, but SNOWstorm has revealed a great deal about the species.

While many assumed that last year's record irruption was caused by hungry owls driven south in search of food, the evidence says the opposite.

"Most snowy owls are in excellent health and extremely fat, and starvation is rarely the cause of death," Weidensaul said.

Researchers now think the irruption was likely related to an abundance of rodents in Quebec that helped the owls produce a large number of young that irrupted into the Lower 48.

In some cases, scientists have been able to document owl behavior they'd previously only suspected, such as the suspicion that snowy owls hunt ducks and other birds over the open ocean at night, using buoys as hunting perches.

They've also learned that snowy owls move onto the frozen surface of the Great Lakes for months at a time, hunting waterfowl in the cracks of ice.

In addition, the transmitters have revealed that individual owls travel dramatically different distances.

"We've seen how some birds are homebodies, rarely straying more than half a mile from where they were tagged, while others traveled hundreds of miles in a few weeks," said Weidensaul.

Necropsies of snowy owls found dead last winter have also revealed the variety of threats the birds face when they venture south, including vehicle and plane collisions, electrocution, and chemical exposure from rodent poisons, mercury and pesticides.

This winter, snowy owls are on the move again, and project participants have come back together to tag, photograph and observe them in hopes of learning more about this mysterious species.

"SNOWstorm is a great example of collaborative science. Many of the people working on this have been studying snowy owls independently for decades, but are now all working in close cooperation."

To see the latest updates from the project, follow the SNOWstorm blog. You can learn more about the group's research efforts in the video below.