Monday, April 08, 2013

Tess, the Count, and Larry the Lizard: Adventures in Symbiosis


Eaglecrest watchers might be familiar with Larry the Lizard, who periodically appears at the mouth of the Barn Owl nest, sunning and catching insects. I'm no lizard expert, but I think 'he' - we don't actually know the gender - might be a northwestern fence lizard. Larry resembles a northwestern fence lizard, lives in fence lizard range, and acts like a fence lizard.

Observers have noticed that Larry and the owls appear to have a symbiotic relationship. While barn owls prefer rodents, they will eat reptiles. However, they don't bother Larry. Is it because he eats ants and other bothersome bugs before they enter the nest? As David McDonald, Eaglecrest's owner, put it, "They look at him, but they don't bother him. He keeps ants and other bugs out of their nest."

Symbiosis has not been documented between northwestern fence lizards and barn owls, but it is known to occur between screech owls and blind snakes in the southwestern United States. Screech owls bring blind snakes - a sightless underground insect hunter that looks somewhat like a long earthworm - into their burrows, where they eat the pests that compete with nestlings for stored owl prey, as well as ants and other insects that could harm the young birds. Some people believe that the owls intentionally use the snakes as nest maids, while others believe that the snakes are dropped during the parent-chick handoff and simply find the burrow a good place to live. Fred Gehlbach, a biologist from Baylor University in Texas, found that snake-occupied screech owl nests produce more and healthier fledglings than do snake-free nests. Once the owl family leaves, the snake crawls down the tree and returns to its underground home. According to Gelbach, blind snakes are common guests of at least four owl species. The snakes we've seen slipping in and out of the nest at Eaglecrest might be performing a similar function.

So it seems at least possible that Larry and the snakes are engaged in a mutually symbiotic relationship with the owls - a relationship between individuals of different species that benefits both. The ants and other pests attracted to the nest's prey remains provide Larry with a steady diet, while the owls reap the benefits of built-in pest control. The snakes may be performing a similar function inside the owls' burrow. As scary as snakes might look to some of us (human) watchers, it is quite possible that they and the lizards are welcome guests.

Thanks to Eaglecrest for giving us a look at Larry!


Symbiosis may be much more common than we think. It comes in a number of different flavors, including:
  • Mutualism:  a relationship between individuals of different species that benefits both.
  • Commensalism: a relationship between individuals of different species in which one species benefits and the other is neither harmed nor helped.
  • Parasitism: a relationship between individuals of different species in which one species benefits and the other is harmed.
We've seen all three of these at the Decorah Bald Eagle nest. I'll return to this subject in a later post. 

Things that helped me learn about this topic: 

2 comments:

Karen Stokes said...

Thanks for the story! We always called those lizards 'blue bellies' when we were kids. Spent many a summer afternoon catching them with little snares made of wild grasses. (Then releasing them, of course!)

AmyRies said...

Karen, thanks for sharing!