It was getting darker and cooler, and traffic was dying down. Time for Mark H.X. Glenshaw to lead one of his owl prowls at Forest Park.
It took only five minutes to find Charles and Sarah, a pair of great horned owls he has been following for eight years. He pointed to a tall tree where they were perched on bare branches near the top. The other six people in his group quickly raised binoculars to their eyes.
The nocturnal birds were just waking up for the evening. They stretched, preened and surveyed the territory. Charles began to hoot, partly to communicate with the missus and partly to keep away intruders.
"How do you know which one is Charles and which one is Sarah?" asked Itai Ben-Shahara, 9, of University City, Mo.
"That's a good question," Mark said. "One way is height. Charles is a big guy, but he's smaller than Sarah. Charles is 20 to 22 inches tall, and Sarah is 22 to 25 inches tall. Another way is color. Charles is lighter than Sarah, and he's more varied in color."
Eventually, the group saw the owls fly and even deliver food -- likely a small bird or rodent -- to their owlets in the hollow of a cottonwood.
Itai and his sister, Noa, really got excited when they found owl pellets of fur and bone on the ground. The birds can't digest these parts of prey, so they cast them out of their mouths.
"I think an owl ate a mouse!" said Noa, 6, poking around with a stick. "No, (the hip bone is) too big for a mouse," said her grandmother, Ellen Hartz, 71.
Ellen is an environmental educator with a special interest in birds. She and her husband, Arthur, are trying to pass on a love of nature to their grandkids.
Also on the owl prowl was retired information technology specialist John Aydelotte, 50, and his 12-year-old son, Cameron, of Webster Groves, Mo.
"I dig birds, especially birds of prey," John said. "We have great horned owls in our neighborhood, and I've heard but not seen barred owls. They have a different call. They're very distinct. And we see red-tailed hawks in our yard every day."
Mark, 41, works as daytime services manager at Fontbonne University's library. By night, he's an amateur naturalist known as the Owl Man.
Mark goes out several nights a week to check on Charles and Sarah, one of two great horned pairs in Forest Park. He has seen them raise 20 owlets.
"This is a very exciting time of year because they've got babies," he told the Hartz and Aydelotte families. "So far, we've only seen two."
Mark allows people to join him on owl prowls if they follow guidelines -- stay quiet, wear muted colors and turn off camera flashes. He won't publicize the location for fear others will chase away Charles and Sarah.
Mark provides the service for free but appreciates donations to Forest Park Forever, a non-profit organization that maintains the park.
The owl study is made possible, in part, by his very understanding girlfriend, Wendy Schlegel, 50, a librarian who has learned to love the birds herself.
"I'm really spoiled," she said. "In the morning, he leaves his videos and photos on the computer for me. So I see a lot of owls, just not in person."
Mark also writes about his adventures at forestparkowlsblogspot.com and gives talks in the St. Louis area. The public is invited to the next one at 7 p.m. April 17 at VFW Post 6632 in Red Bud. It's sponsored by Kaskaskia Valley Audubon Society.
Mark moved to St. Louis in 1995 to study history and communication at Washington University. An interest in wildlife prompted him to explore the woods and waterways of Forest Park, where he stumbled on Charles and Sarah in 2005.
"In a brief period, I saw the two owls hoot together in a duet," he said. "It was a very beautiful vocal and visual display. And then I saw them fly, and they are very fast and powerful and graceful in flight.
"And then, if that wasn't enough -- and it was -- there was a real cherry-on-top moment, when one of them chased a great blue heron that was twice its size, and (the heron) was hasty and terrified in its departure."
The owl sighting was a life-changing event for Mark, who has followed up with extensive research and now owns 40 books on owls.
He has observed Charles and Sarah hunting, mating, casting out pellets and raising their young. Owlets hang around for months before striking out on their own.
Mark isn't the only regular owl-watcher at Forest Park. He has mentored several people, including Brenda Hente, 49, of St. Ann, Mo.
"Mark has this sixth sense about (owls)," she said. "He'll be like, 'They might be over there,' and we'll look, and there they are. And he's very patient with people when he brings them out here. He wants them to experience this, as long as they are respectful of the owls and their territory."
At a glance
What: Talk on "Forest Park Owls: Hidden in Plain Sight"
Who: Mark H.X. Glenshaw, the Owl Man
When: 7 p.m. April 17
Where: VFW Post 6632, 830 S. Main in Red Bud
Information: Visit the Kaskaskia Valley Audubon Society website at e-kvas.org/programs.html
Owl prowls: Write Mark at email@example.com