RUSSELL SPRINGS -- After eight days of operating under cover of darkness, 45 highly endangered black-footed ferrets were captured, according to Dan Mulhern, a wildlife biologist with the U.S. Fish and Wildlife Service.

The darkness is a necessary cover, as the ferrets are nocturnal and can only be found when high-intensity lights find the bright emerald green reflections from their eyes.

Mulhern isn't sure how many other ferrets were spotted, but not captured, and is busy trying to figure that out.

"I'm sure we're well up over 50," he said of the total number of ferrets that were spotted during the two-week stint in the field surveying the animals, part of a reintroduction project that started when the agency released animals in December 2007.

He suspects the number of ferrets spotted will remain below 60, but by how much, he's uncertain.

"It's at least 45," Mulhern said of how many ferrets are on the ground at two sites in Logan County, the Haverfield/Barnhardt complex, a 10,000-acre ranch south of Russell Springs, and the 16,800-acre Smoky Valley Ranch owned by the Nature Conservancy, located southwest of Oakley.

Mulhern was joined by almost 45 volunteers during the past two weeks, taking to the fields at night criss-crossing the two ranches, hoping to spot the emerald green eyes of the ferrets.

Once spotted, they were trapped, vaccinated and checked to see if they had been chipped, signifying that they had been captured before.

Most of the 45 captured were unchipped, Mulhern said.

"The vast majority were native born," he said, citing the lack of electronic chips. "We've got a few animals that are hanging on from previous releases."

But the 45 is a sharp increase from the 29 that were captured last spring.

Mulhern said that's to be expected, considering the kits that were born this summer and now are on the ground.

"We always anticipate the fall capture should be higher than the spring," he said.

He's still ready for a few more animals to be released later this fall.

Already, 14 animals were released on TNC ground, and additional animals should be available later. They likely will be released on the Haverfield/Barnhardt complex.

Mulhern said he's unsure how many will be available for release, but he suspects the total might be close to the 30 he originally requested for this fall.