Odd migration patterns trouble zoologists

There are lots of waterfowl but usually not many sightings of snowy owls at the Edwin B. Forsythe Wildlife Refuge. TOM GRALISH / Staff Photographer
Posted: December 23, 2013

GALLOWAY TOWNSHIP, N.J. - Seeing a rare species like the arctic-dwelling snowy owl so close to home was both thrilling and disconcerting for avid birder Lon James.

James, a native of the Philippines who now lives in Philadelphia, had arrived at the Edwin B. Forsythe National Wildlife Refuge with a camera and several large lenses expecting to spend hours searching, and waiting for his chance to glimpse the large owl species.

These birds usually winter in the northern circumpolar region - from the arctic tundra down through the northernmost stretches of Canada and Alaska - but have been spotted recently as far south as Tennessee.

And their apparently abundant number in New Jersey this year - there are usually between none and three spotted in the Garden State annually - with reports of nearly two dozen of the birds in the state, has researchers on alert.


In New Jersey, it's been a "crazy year" for the owls, which some scientists say number in the dozens, possibly hundreds, across North America. Commensurately, the influx of the unusual species has birders flocking to Forsythe, according to Don Freiday, visitor services manager at the wildlife refuge.

"We had about 2,000 cars come through so far in December, and that's two times the number we usually have for this same period," Freiday said.

So earlier this month, only minutes after entering the eight-mile nature drive that rings the salt marshes and tidal pools within the 43,000-acre reserve off this Atlantic County municipality, James, 58, was snapping shot after shot of the white-plumaged owl.

"That tells me there are a lot of them around," said James, who has been shooting nature photos since he was a teen. "Which is really cool, but it's also a little scary. You have to wonder why so many of these birds are so far south this year . . . why they are not where they are supposed to be."

That is the question that concerns researchers like David Wilcove.

"Snowy owls are a special case, because every few years we do see them migrating further south than usual," said Wilcove, a professor of ecology and evolutionary biology at the Woodrow Wilson School at Princeton University.

Wilcove, a leading expert on species migration patterns, said the arctic owls' making southerly appearances follows a pattern of increasing and then decreasing populations. In years where there are an abundant number of the birds, they may be forced to forage for food further from their usual climes, he said.

"When populations build up, they kind of get pushed out of their usual habitat and displaced to other areas," said Wilcove, who in 2008 wrote No Way Home, a book about changes in species migratory patterns. "It's not like clockwork. It's more related to changes in the food supplies from year to year."

Wilcove said it's not surprising to see snowy owls so far south, but the "big invasion" of them is unusual.

Experts, however, have no clear-cut answers about the influx of the birds into more southern areas, said Kevin McGowan, an ornithologist who has been studying such patterns for more than 25 years at Cornell University's Lab of Ornithology.

McGowan said the change could indicate an abundance of food sources for the birds in the arctic, leading to more births than ever before. Or, he said, it could mean that climate change could be curtailing food supplies, forcing the birds to venture out of their usual areas in search of nourishment.

But species being in places they aren't supposed to be continues to interest biologists.

Wilcove said the most concerning issue this year may be the annual migration of the monarch butterfly. Usually millions of monarchs arrive in central Mexico by mid-November, creating one of the most extraordinary migrations on the planet. By mid-December, only about three million - instead of the usual hundreds of millions - had arrived, Wilcove said.

The butterflies funnel into a tiny area in Mexico to roost for the winter before heading to the U.S. Gulf states, where they will lay their eggs and then die. Those eggs develop into the next generation of monarchs, which continue migrating north and then lay their eggs and die. It takes about three or four of these generations to repopulate the eastern United States and Canada. With so few monarchs arriving by this late date, it is an "alarming possibility" that the population has crashed, Wilcove said.

Possible causes for this crash could be the increased logging operations in the area of Mexico where the butterflies winter or the genetic modification of food crops. Crops on factory farms have been altered so they can withstand the application of herbicides to eliminate weeds, like milkweed and others. The butterflies depend on milkweed flowers to lay their eggs on and supply sustenance, Wilcove said.

At the same time, right whales off the New England coast didn't show up in their usual breeding grounds either. Among the rarest mammals on Earth - biologists say there are only a few hundred left - a large percentage of the population usually spends summers in the Bay of Fundy, off Maine and Nova Scotia, to feed on the zooplankton in the water. This year, few showed up - although researchers don't believe the animals have died, but rather found an area elsewhere to feed on more abundant zooplankton, Wilcove said.

In East Africa, the wildebeest population also did an odd about-face this past summer, too. About a million of the animals move between Kenya and Tanzania in vast herds in response to seasonal rains that turn the Serengeti plains into a lush grazing area. A drought in the region this year forced the wildebeests out of Tanzania back to Kenya early. Climate change could be affecting rain patterns - and migration - by moving the animals away from protected areas to graze on the grasses in regions of the continent where they aren't protected from hunting and poaching, according to researchers.

"I think we're seeing the disruptions in the animal migration in large part because we're impacting the environment," Wilcove contends. "And these are all early warning signs."





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