MNN - Mother Nature Network

It’s a bird … it’s a plane … it’s — a bat? That’s the question ornithologists have long asked about the troglodyte bat bird of South America (well, maybe minus the “plane” part). New Scientist features the strange creature — colloquially known as the oilbird, thanks to a diet rich in the fruit of the oil palm — in its Zoologger column this week, where it sheds some light on these nocturnal birds.

 

First and foremost, they are, in fact, birds. Despite possessing a number of bat-like characteristics such as using echolocation to perceive their surroundings, roosting in caves by the thousands, and covering the floors of said caves in a thick layer of guano, the oilbird has feathers and lays eggs. 

 

Another trait that sets the oilbird apart from its bat doppelgangers is its incredibly sensitive eyes: The cave-dwelling species enjoys extremely powerful night vision thanks to about 1 million light receptors packed into every square millimeter of their retinas.

 

Perhaps the most surprising fact about these distinctive feathered creatures is how much time they spend outside during the day. A new study led by Richard Holland of the Max Planck Institute for Ornithology in Radolfzell, Germany, showed that the little birds, which were once thought to avoid the sun by spending daylight hours in their home caves, actually spend a good portion of their lives outside during the day. Holland and his colleagues made the important discovery when they tagged 12 oilbirds in a Venezuela cave. The miniature GPS trackers attached to the birds showed that the birds tend to spend two out of three days roosting in trees — a discovery which demonstrates the oilbird’s ecological importance.

 

If oilbirds were to spend all day in a cave, the many seeds they eat would fall to the cave floor with no chance of taking root. But because the birds spend so much time roosting in trees during the day, a large number of the seeds they consume land on the fertile forest floor, where they enjoy a much better chance of survival.