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.
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...
(http://pixabay.com/en/snake-cartoon-game-ladder-python-36376/)
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"
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.
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