The images are arresting: An ATV stops in a sunny meadow filled with knee-high grasses. Its driver, a young woman, removes her helmet and looks directly into the camera, a strip of black duct tape stretched across her mouth. A bird hunter in full camouflage is likewise muzzled by tape, as is a fisherman on a riverbank, an older couple backed by snowy mountains, and a rancher beside horse corrals.

Meanwhile, an ominous voiceover describes House Bill 1505 –– "a plan that gives the Department of Homeland Security complete control over millions of acres of Montana public lands." It implores viewers to contact the bill's co-sponsor, Republican Dennis Rehberg, Montana's sole U.S. House representative, warning: "We'd have no say if Rehberg gets his way."

This 30-second commercial and a similar one aired for three weeks last October in and around Billings, Missoula and Kalispell, at a cost of more than $200,000. Media buys of that size are to be expected heading into a big election year: Rehberg is challenging Sen. Jon Tester, D,  in a race that could decide the Senate's balance. What is surprising, however, is who paid for the ads: Montana Hunters and Anglers Action. MHAA is a 501(c)(4), a nonprofit that, under federal law, can spend money to support or oppose candidates without disclosing its donors.

Political activism among hunters and anglers is nothing new, in Montana or nationwide. But the six-month-old MHAA exemplifies a more particular modern trend. Over the last 10 years, conservation-minded hunters and anglers have attempted to put environmental stewardship back at the center of sportsmen's political agenda. And lately, a few groups, such as MHAA, have become increasingly aggressive. Following the strategic lead of secretive entities like Crossroads GPS -- Karl Rove's conservative 501(c)(4), which uses political advertising to influence elections -- they're spending money to elect individuals who champion large-scale land and wildlife conservation, and to defeat those who don't.

"At the end of the day, these politicians like being elected," MHAA president Land Tawney remarks on an icy January day as he carries his 3-year-old daughter Cidney up a Missoula hiking trail. "If you help get a champion elected or if you beat someone based on their bad record, that's when the true power starts to come."

Tawney, 37, has a ruddy complexion and a trim orange beard. He's worked on sportsmen's issues since earning his undergraduate degree in wildlife biology from the University of Montana in 2000. As a senior manager for the National Wildlife Federation, he works primarily on reforming federal mining law.

Land's father, Phil -- a former executive director of the Montana Democratic Party -- founded the state's first political action committee for sportsmen, the Montana Hunters and Anglers PAC, about 30 years ago. When he died in 1995, the organization stagnated. But in 2009, Land began to rebuild it. In 2010, it focused on a legislative race in Billings, supporting Democratic state Rep. Kendall Van Dyk, who was challenging Republican Roy Brown for his state Senate seat. Van Dyk, former chairman of the Fish, Wildlife, and Parks Committee in the state's House of Representatives, touted his sponsorship of the state's 2009 stream-access law, which clarifies the public's right to access streams passing through private property from public bridges. Brown, a former petroleum engineer, ran on his business credentials, but struggled to shake his oil-industry connections, which hamstrung his 2008 gubernatorial bid. Tawney's PAC paid for one TV ad and several mailers, including an oversized postcard that depicted Van Dyk posing at river's edge with a freshly caught fish. The other side showed a poodle wearing a Brown banner beneath the words: "Roy Brown: That Dog Don't Hunt." Other PACs and donors jumped in as well, and the contest became the most expensive legislative race in state history, with over $200,000 spent. Van Dyk won in a recount by just four votes.

Van Dyk, now vice president of the MHAA, says the race's momentum carried into the 2011 legislative session. The stream-access law, which is popular with anglers, was challenged by a bill that passed the House and faced a hearing in the Senate. A large crowd was anticipated, so the hearing was moved to the old Supreme Court Chambers of the state capital building. "When you walked in that room, you knew what was going to happen," Van Dyk says. "Those guys were pissed." Over 300 opponents showed up, and the bill failed to move any further.

"At that point, I realized the magnitude of this constituency," he says. "We needed to have a more organized voice." A year and a half later, he and Tawney filed the paperwork for MHAA to become a 501(c)(4). Within weeks, they were running ads criticizing Rehberg. Tawney says the group will spend more on that race, but won't disclose how much or the source of the funds.