BAXTER STATE PARK – Renowned wildlife and nature photographer William Silliker Jr. died of an apparent heart attack Monday morning on the Roaring Brook Trail at Baxter State Park, according to authorities.

Silliker shot pictures for the popular Baxter State Park Maine Moose Watcher calendars from 1997 to this coming year, and his photos were featured in the park’s visitors center. Baxter Park Director Irvin Caverly, who completed a video titled “Nature at Peace” with Silliker, said the photographer was a frequent visitor to the park and was dedicated to the preservation of its resources and wildlife.

“He was really easygoing, very sincere, and a person any of us would be glad to call a friend, Caverly said Monday. “It’s a tragic, tragic event.”

Although he couldn’t be sure, Caverly said there was a possibility Silliker was working Monday on pictures for the park’s 2005 calendar.

Silliker, who was in his 50s, was leading a group of at least a half-dozen photographers who were at the park taking pictures of moose, according to Millinocket Fire Chief Tom Malcolm. The group apparently was past the second bridge on the trail when Silliker grabbed his chest just after 7:30 a.m. and dropped to the ground, Malcolm said.

Emergency crews came to the spot a half-mile in from the campground and found Silliker lying on the ground with no detectable pulse or vital signs, Malcolm said. A doctor and a nurse in Silliker’s group had performed CPR, and rescue personnel used defibrillator paddles to try to revive him, Malcolm said, but were unable to do so after a half-hour.

Known to many in photography circles as “The Mooseman,” Silliker had his pictures published in magazines including Audubon, Backpacker, Down East, Field & Stream, National Geographic, Outdoor Life, Outdoor Photographer and Sports Afield, among others, according to his Web site, www.camerahunter.com.

Silliker’s pictures also have been featured on ESPN, the Discovery Channel, NBC’s “Today” show, and his recent clients included L.L. Bean, The Nature Conservancy, Outdoor Photographer magazine, the Forest Society of Maine and the Trust For Public Land. He served as a columnist for the Bangor Daily News, the Portland Sunday Telegram and the Maine Sportsman and gave regular workshops and slide show lectures for local camera clubs.

When he wasn’t taking pictures, Silliker also co-chaired the ethics committee of the North American Nature Photography Association and served on the Maine Department of Inland Fisheries and Wildlife Non-game Advisory Council from 1992 to 1998, according to his Web site.