"PLUM ISLAND — The Parker River National Wildlife Refuge usually gets noticed when a rare bird turns up there, but now the sheer number of a common species is gaining attention.

Hundreds of thousands of tree swallows from across New England and southern Canada have begun gathering at the refuge in preparation for their fall migration.

The 5- to 6-inch long birds, with white bellies and shiny blue-black backs and heads, converge from distant nesting spots and migrate in huge flocks, appearing as swarms across the refuge landscape.

The swallows travel in such large numbers for protection, refuge wildlife biologist Nancy Pau said.

"If you're in a flock of 200,000 birds, there's less chance of you getting picked off by a predator than if you were on your own," Pau said.

Plum Island provides a number of ingredients that are attractive for the swallows as they gear up for their flights, she said.

"We have a lot of berries and a lot of insects," Pau said. "It's a very good habitat."

The refuge also has good vegetation cover for the tiny birds to roost in, she said.

Pau said refuge staffers began noticing a significant upswing in the number of swallows two years ago.

She said the migration will peak in late August. Right now, she said, birds are coming into the refuge, forming large flocks and taking off. Their place is then taken by more swallows, forming more large flocks.

The process of gathering and getting ready for migration is called "staging," said Kate Toniolo, the refuge's supervisory park ranger.

They gorge themselves on the island's bayberries, which are high in fat and give them enough energy to make their long journey to the southern U.S. and Central America.

Tens of thousands of swallows can be seen at a time, Toniolo said.

"It's a pretty spectacular sight," Pau said." (Victor Tine, Newburyport [Mass.] Daily News, August 14, 2008)