I arrived at my field site (Blue Oak Ranch Reserve) a little over a week ago. Work has been pretty slow as we are trying to capture rattlesnakes to implant radio transmitters into. Three days ago, we ended work early and were hanging out at the field station (a large barn). I noticed snake-like slithering near the roof of the barn so I looked up. Lo and behold a gopher snake (Pituophis catenifer) had weaseled its way (or shall I say “snaked” its way) about thirty feet up the barn wall! At first, I thought this sight of the wall-climbing snake was strange, but then I realized that it was heading straight towards a bird’s nest. I became extremely excited as I had never seen a snake ambush birds before. I got out my camera and started to record the snake.
Although I mainly think of gopher snakes as ambushing squirrel pups inside their burrows, these snakes are common bird nest predators, and will go for both cavity-nesting and open-nesting bird species. A study performed by Eichholz and Koenig In central California (1992) found that approximately 21% of bluebird nests and 36% of nest failures are caused by snakes, making snakes the primary cause of nest mortality. They also found that gopher snakes do not randomly search tress for nests, but only climb those with active nests. This suggests that they have the ability to detect bird nests from the ground (probably by picking up chemical cues). These snakes seem to prefer eating baby birds instead of eggs, and their preference increases as the babies grow older. Another report by Czaplewski et al. (2012) describes a gopher snake making a dangerous climb to ambush cliff swallow nests in Utah. The authors’ note the appearance of several small food items in the snake’s belly.
Gopher snake browsing on cliff swallow morsels (taken fromCzaplewski et al. 2012)
Back to my story, the snake appeared to be entering the bird nest when it suddenly became very still. I waited for it to continue its movement into the nest, however it started to twist and squirm. It had become tangled in plastic mesh netting on which the nest was built. Unable to reach the snake, I thought for sure it would die.
If only snakes could use ladders, then bad things wouldn't happen...
As it remained motionless stuck within the netting, a wren approached the snake and made loud calling sounds. This could have been the mother bird defending her eggs. Many birds will make specific alarm calls in response to snake predators. A recent study shows that Japanese great tits (Parus major minor) produce alarm calls that encode information about the type of predator (Suzuki 2014). These birds use a “jar” call for snake predators and a “chicka” call for crows and martens (a type of weasel). These calls are thought to warn offspring and other birds, but they may also deter the snake from further pursuit of the nest (something called pursuit-deterrent signaling). My current research examines the use of pursuit-deterrent signaling in California ground squirrels against rattlesnake predators.
View the whole gopher snake story on the Youtube video above!
The gopher snake remained stuck in the mesh netting near the roof of the barn, and I thought for sure it would die. However, Erik, the reserve steward came to the rescue! He found a tall ladder that he used to reach the snake and remove it from the barn wall. The snake remained tangled in the mesh and we had to cut it out. Poor snake had ripped some of its skin open trying to free itself. I applied anti-septic liquid bandage to its cuts, and am now keeping it in captivity so that its skin can heal. I will release it soon so it may resume its daredevil climbs.
Erik was this snake's "knight in shining armor"
The gophie really did a number on itself. Luckily, we were able to cut away the mesh.
Czaplewski, N. J., K. S. Smith, J. Johnson, C. Dockery, B. Mason, and I. D. Browne. 2012. Gopher Snake Searching Cliff Swallow Nests in East Central Utah. Western North American Naturalist 72:96–99.
Eichholz, M. W., and W. D. Koenig. 1992. Gopher Snake Attraction to Birds’ Nests. The Southwestern Naturalist 37:293–298.
Suzuki, T. N. 2014. Communication about predator type by a bird using discrete, graded and combinatorial variation in alarm calls. Animal Behaviour 87:59–65.