As natural gas drilling activity continues to escalate in Pennsylvania -- as of April 27, the state had issued 10,675 Marcellus permits and 5,314 wells had been drilled -- the question remains as to what impact this industrial activity will have on the state's wildlife.

Plenty of concerns have been raised.

In 2010, the Nature Conservancy issued a report predicting that energy development overall in the next two decades -- from wind turbines to natural gas drilling pads -- could alter up to 40 percent of the state's most ecologically valuable large forest blocks, endangering habitats of species from songbirds to trout.

But reports about what is actually happening are scarce.

This week, the Wildlife Conservation Society highlighted a report that appeared in the March issue of the journal Biological Conservation. It documented "that intense development of the two largest natural gas fields in the continental U.S. are driving away some wildlife from their traditional wintering grounds," the WCS reported.

Over a period of five years, researchers tracked 125 female pronghorns via GPS collars in Wyoming's gas fields.  They found that the animals are being driven "to the periphery of areas historically classified as crucial winter ranges." They also found that the best-quality habitat for the pronghorns had declined by 82 percent.

Fifty percent of North America's pronghorn live in Wyoming.

"In our study we have detected behavioral shifts for pronghorn in response to natural gas field development and infrastructure on federal BLM lands," said Jon Beckmann of WCS's North America Program and lead author. "By detecting behavioral changes, it is possible to identify threshold levels of gas field infrastructure development before any significant population declines. Maintaining the integrity of crucial wintering areas is particularly important in harsh winters to avoid diminishing pronghorn numbers."

WCS has developed recommendations to protect pronghorn on BLM lands, according to a press release from the society. They include collecting baseline data on population sizes and distribution prior to energy development. This could be used to identify crucial habitat and restrict or redirect  development  in those areas.

Authors include Jon Beckmann and Rene Seidler of WCS; Kim Murray of Institute for Systems Biology; and Joel Berger of the University of Montana and WCS.

The industry has attempted to lessen impacts. Responding to the Nature Conservancy report in 2010, Kathryn Klaber of the Marcellus Shale Coalition said that some of the recommended mitigation measures are already being used by an industry that has made "major leaps" in lessening its impact. For instance, drilling companies already put more wells on a single well pad, as the report recommends. And they are sharing access roads rather than building separate ones because it also makes economic sense.

UPDATE:  A coalition spokesman has taken issue with this post. "While I'm sure many southeastern Pennsylvanians are uniquely concerned about the Wyoming pronghorn, why not tell your readers what natural gas producers are actually doing in PA as it relates to conservation?" he wrote in an email.

That wasn't my point, of course. The point was that data-driven studies of what actually happens in the world of wildlife are rare, and this was one of them.

But he nevertheless wishes to note -- and I'm happy to do it -- that on April 26, the industry released the first in a series of "recommended practices" for natural gas developers. It focused on site planning, development and restoration -- all of which obviously could impact wildlife, for better or worse.

Among the recommendations, the 34-page document "encourages" operators to seek input from sportsmen's organizations, hunting and fishing clubs and the like "to learn about unique local conditions that could affect fish, game and plant species. Operators should consider opportunities to adjust their site planning to be responsive to local conditions and seasonal issues related to breeding and spawning seasons of fish, game and wildlife in general."

Another one: "Operators should be willing to modify plans to account for reasonable requests for such items as access road retention, pond retention, wildlife habitat improvements, vegetative screening, site drainage improvements and swales, and the creation of habitat features like brush piles, vernal ponds, and nesting or cover areas."