Two years ago, twins Karen Hogan and Teresa Noel discovered a new passion: birding on national wildlife refuges. "We went to Shiawassee, then to Muscatatuck," says Hogan. "We fell in love with the beauty, the nature." What could beat that? Suddenly, she knew: "We should go see every one of them."

So the pair plans to bird on all 460 or so refuges open to the public.

Never mind that some, like Guam National Wildlife Refuge, are in the remote Pacific, or, like Arctic Refuge, in northern Alaska. So what if the sisters aren't rich (both manage biomedical research labs, Hogan at the University of North Carolina; Noel at the University of Kentucky) or carefree (Hogan has a husband and grandkids; Noel, single, helps care for her elderly mother). So what if friends and family question their sanity?

"If your dream doesn't scare you, you shouldn't do it, right?" says Hogan, laughing. By making several frugal, multi-refuge trips a year, they estimate the project will take 10 years and $40,000.

Already, the two have logged more than 50 refuges - mostly in Florida, North Dakota, Tennessee and North Carolina. Lower New England is on tap for May. They blog about their adventures at www.birdingwithkarenandteresa.com.

Ask them highlights of their travels, and they reel off memory after excited memory. "Hearing yellow-headed blackbirds at Arrowwood" Refuge in North Dakota, says Noel. "I'll never forget that. A bunch of them were singing at the same time. I just loved it."

Adds Hogan: "There were birds flying in every direction, swallows, flycatchers, bobolinks, terns, sandpipers and ducks. I felt like my head was on a swivel. I didn't know which way to look."

Noel found Arthur R. Marshall Loxahatchee Refuge in Florida a "magical place. That's where we saw a bobcat," she says. "It came within 10 feet of us."

At Pocosin Lakes Refuge, NC, Hogan filmed snow geese in flight. "I can't imagine anyone seeing these amazing birds and not wanting to preserve them for future generations," she says, her voice breathless with emotion.

The sisters, in their mid-50s, inspire admiration of their own. "They're a couple of amazing women," says Okefenokee Refuge manager Michael Lusk, who chanced upon them at 7 a.m. New Year's Day at Crystal River Refuge in Florida, where he was then based.

The hour was not usual. Hogan and Noel's basic refuge trip plan: Arrive at dawn. Explore. Snack in car. Move on. Repeat - into the night, if possible.

"You cannot waste a minute to go get food or anything," says Noel. "We eat tunafish out of a can, crackers, so we're not running into town to get food. Every daylight hour is spent in the refuge to get as much out of it as we can."

They ply staff and volunteers with questions: Why don't more people know about refuges? If more people visit, is that good? Or will that disturb wildlife? "Very thoughtful, philosophical questions," Lusk says. They're "very impressive women who really 'get' what refuges do."

Noel says the Florida trip underscored how vital wildlife habitat is - and how fragmented. "I met a Florida scrub jay at Merritt Island." It perched on her cap, then her hand. "It's kind of sad. There's [practically] no place for them to live."

But the twin's spirits don't stay down long. "We like to tease each other: Who has the most birds?" says Noel. "We both have life lists. I'm sure she is ahead. She lives on the coast. I live in downtown Lexington. She gets so many more birds than I do."

Psyched for the next trip? "I can't wait," Noel says. "I wish I could do it every month."

Susan Morse is a writer-editor in the Refuge System Branch of Communications.