The first owl perched in a pecan tree and watched. A new and unwelcome owl was making noise in its territory at the Medina River Natural Area.

On the ground, urban wildlife biologist Richard Heilbrun waited as well. He and his amplified owl call were actually the new owl — looking to pick a fight.

The second Saturday of each month, the nature area offers a program that highlights either attractions of the preserve, the wildlife of Texas or conservation.

Last Saturday night, Heilbrun hosted Creatures of the Night, a once-a-year affair for which he is allowed to break one of the preserve rules and play recorded bird noises that will distract the barred owls from their evening hunt to come and defend their territory.

Most nights the chirps of crickets and croaks of frogs have to compete only with the rumble of traffic on Texas 16 and the murmur of classic rock and Tejano music coming from the Route Five Lounge.

Then the owls mostly go about their nightly business of catching small mammals.

Gail Dugelby manages the preserve and gives permission for the recordings.

She said she limits the program to once a year because of the additional stress they cause.

“It’s like if a stranger came into your house,” she said. “Even if they don’t take anything, it takes you a while to get back to normal.”

But the chance to share with the public the experience of seeing owls in the wild for 45 minutes to an hour is worth the confusion it brings the owls.

The owls have two calls they use to figure out who is in their territory.

“The first is ‘who-who-who cooks for you, who-who-who cooks for ya’ll,’?? Heilbrun said. That’s the call owls make to each other when they are just trying to find out who’s nearby.

The second call is “who-who-who-who.” That’s used when owls are trying to flush out an owl that is either being unresponsive or hiding in a tree.

That’s what Heilbrun was waiting for as he and 85 after-hours visitors to the preserve sat in silence along the riverbank straining to see the outline of the owl by the light of a waxing gibbous moon.

Finally, the owl was coaxed into making calls, and “who-who-who” bounced back and forth from the ground to the trees. Two more owls came to check on the commotion.

The owls have a third call that sounds like the scream of a howler monkey. Heilbrun explained it’s a competition for dominance. Once an owl starts, the calm of the night is gone and the birds screech at each other like neighbors yelling over a backyard fence.

When the fight gets going, the owls ignore everything else, Heilbrun said, and even the spotlights that were then shone up into the trees did not seem to bother them.

With the trees lit up by 20 or more lights, the owls could easily be seen peering down. One took flight, spreading its 40-inch wings, and glided silently to a closer branch.

The bird’s massive talons were clutched into loose fists.

Then the owls quieted down, and Heilbrun made the call to let them be.

This article originally appeared in the Nov. 10 San Antonio Express-News.