Through the open top of the double door came loud, insistent chatter. Bird chatter, that is. One of the house wren parents was sounding an alarm call, a repeated burst of short chatter. The adult wrens did it if we were in the yard as they approached their nest.
Clearly this bird recognized a threat. We went outside to investigate. Sure enough, sitting on the kitchen windowsill was a three-foot gopher snake. It was probably the same snake we had seen a few days before, crossing the street toward the eco-reserve.
Now it was back, and eyeing the wren nest in the birdhouse. Soon, an agitated hummingbird and a curious house finch flew over and joined us. All this time the wren kept up its repetitive calls.
When the neighbor and her daughter came over, the snake decided it was time to leave. It slipped gracefully off the sill, down over the garden chairs, and hid under the hose reel. Eventually it glided into the shrubbery. Only when it was completely invisible did the wren stop calling.
The last time I heard this alarm call from a bird was many years ago when I kept quail for my research at UCI. They lived in cages hanging from the wall in a large room.
One day I entered the bird house to the sound of sharp, repetitive clucks. All the quail were alert, clucking, and looking down, where a gopher snake lay sprawled across the floor.
On a sonograph (an instrument that displays sound waves on a screen), the sharp calls appear as concentrated bursts of sound, each with an abrupt beginning and end. This type of sound is easy to locate, so any animal close enough to hear it knows where the danger is.
Small mammals like squirrels and chipmunks also make the same kind of alarm calls: repeating sharp barks that continue until the danger is no longer visible. You’ve probably heard it many times from the local ground squirrels.
Our chickens also clucked when they saw a ground predator; but when danger was in the sky, their response was quite different. When a hawk or vulture flew overheard, one of the chickens sang a long, ethereal, one note call, that started softly, built in intensity, and gradually faded away. It seemed to come from everyplace at once. Each chicken cocked her head and looked into the sky.
On the sonograph, this call looked like a long, thin sausage with elongated, pointy ends. Calls with this signature are difficult to locate, so the hawk couldn’t use it to backtrack to the calling bird.
I wouldn’t be surprised if other species use a similar call for danger overhead. It can’t be a coincidence that mammals and birds use the same alarm call for an intruder approaching on the ground. In a community composed of different animals, potentially all can be warned by a single lookout.