It was a mystery -- one befitting a Hardy Boys or Nancy Drew adventure.

The story begins at dawn when a discovery haunts a household in Tucson, Ariz. A crime, of sorts, had been committed in the darkness of night.

This was only the beginning of the tale.

The greedy bandit or bandits -- it was hard to know the number -- returned night after night to the bounty, unseen while the neighborhood slept. By morning, the perpetrators had flown into obscurity, their trail undetectable in the daylight. Only the evidence of their heist remained.

Hummingbird feeders, daily filled with sugary liquid, stood empty in the awakening light.

My friends, modern-day sleuths Mel and Deirdre Mashman, set about to investigate why the free lunch for the hummingbirds had been stolen away in the gloom. Armed with coffee and a camera, the two homeowners sat quietly in the shadows.

Their midnight watch proved worth the wait.

One by one, the looters descended on the quiet scene, their radar honing in on a quick meal. Like birds they flew at the feeders, setting them in motion.

"I was sure," Mel related about the initial backyard sighting, "these were bats, but I didn't know what kind."

FLASH!

The camera caught the nighttime visitors in the act of sucking the plastic orbs dry. Still, the multiple photos that pierced the darkness didn't seem to discourage the hungry mammals.

Detective work followed the next day when Mel and Deirdre learned they had witnessed nectar bats. Evidently, two species migrate from Mexico -- and even farther south -- to the southeastern Arizona desert between April and October. The flowering cactus and agave lure them there -- and an occasional hummingbird feeder, an extra reward for their effort.

Catching them on film solved the "whodunit," but the case isn't closed. My friends' backyard feeders are filled to the brim for birds by day and bats by night.

Visit this link to watch their slideshow of the night the nectar bats sneaked in for a bite. It's a thriller.