Wildlife biologist Dan Mulhern is at a loss to explain why so few black footed ferrets were found recently in what was once the most important reintroduction site in the nation.

Mulhern, a biologist with U.S. Fish and Wildlife Service, and his crew of 27 recently spent the equivalent of nearly nine days driving through pastures after dark in search of the solitary weasels.

The searchers spent their nights sweeping strong beams of light back and forth in the pastures, looking for the tell-tale emerald green reflection of a ferret's eyes.

By the time the survey was completed, Mulhern reported, just six individual ferrets were observed, the lowest number since the animals were first reintroduced into Logan County in December 2007.

The only time a lower number has been found was in August of last year, when only five were found during a summer survey designed to find groups of ferrets. Because they are normally extremely solitary, it's uncommon to see groups of ferrets together other than a female with her kits.

It's the latest survey that's a concern, however, and it's the smallest number found during either a spring or fall survey since the initial release of 24 animals in December 2007. The following March, spotlighters found just eight animals.

The surveyors this spring found just two males and three females, all but one of them on what is known as the Haverfield-Barnhardt complex south of Russell Springs.

A single animal, believed to be a female, was found on the Smoky Valley Ranch owned by the Nature Conservancy.

Last fall, 22 ferrets were found, five of them on Nature Conservancy land.

"I don't know what's going on," Mulhern said of why the ferret population numbers continue to decline.

He said some of the prairie dog habitat "looked very decent," especially on the nearly 10,000-acre Haverfield complex. That's a tentative assessment, Mulhern said, because both sites were only seen at night, but there were signs of active use by the prairie dogs that ferrets depend on for both food and shelter.

"We saw lots and lots and lots and lots of swift foxes," he said, "and quite a few coyotes."

It's the weather, however, that Mulhern said has had the greatest effect on ferret numbers due to poor conditions in the field and a collapse in prairie dog numbers in 2010.

"The No. 1 thing we need is rain," he said. "It's as bad looking as I've ever seen it."

Prairie dog numbers have rebounded somewhat, he said, but continue to struggle as the drought persists.

"This is a very puzzling situation out here," he said.

FWS continues to work on hammering out details of how to proceed with the reintroduction project, now 15 months past the initial project that was permitted to last five years.

The greatest sticking point right now, he said, is reaching an agreement with the agency's partners on money available for controlling prairie dogs on adjoining lands.

Initially, FWS, the Nature Conservancy and Kansas Department of Wildlife, Parks and Tourism contributed equal amounts of money -- nearly $25,000 a year -- to pay the cost of poisoning prairie dogs migrating onto adjoining lands. The U.S. Department of Agriculture's Wildlife Services agency contributed the manpower to do the work.

"It's been difficult getting people involved together," he said.

But it's critical to continue to offer the option, Mulhern said, to help reduce objections to the project from adjoining landowners.

Once a number of local issues are resolved, he said, the decision on how best to proceed with the project will be made in conjunction with the agency's regional office in Denver, Mulhern said.

Those decisions also likely will need to be made before Mulhern can call for the release of additional ferrets on the two reintroduction sites.