By: Jim Pauff, Travis Audubon Master Birder
It isn’t that banders don’t like gray catbirds (Dumetella carolinensis), it’s that some days there are so many of them dangling in the nets one gets sick of looking at them. You get sick of hearing them complain about being caught. They use avian profanity equaled only by red-eyed vireos. If you walk past them to untangle another bird first they cluck loudly at you like insulted hens. Catbirds are interesting not because they are so delicate or rare or beautiful but because they are so self-aware. Look into the eye of a gorgeous little magnolia warbler and nothing glimmers back but a shiny black void. Look into the chestnut-colored eye of a catbird and it sizes you up, like a tiny dinosaur. Catbirds know who and what they are, and nets and banders get in the way of them being themselves.
When singing, gray catbirds typically sit hunched over, babbling rather quietly to themselves. They are the poorest impersonators of the three eastern Mimidae. But research shows their lack of precision is fine with them. Specifics have not been worked out yet but it seems song deviation is a mating strategy for male catbirds. According to a study done at the University of Massachusetts in 1997, catbirds put more emphasis on developing unique repertoires than getting other birds’ songs down note for note—à la mockingbirds. Catbirds are born with imaginations. Baby catbirds in the study were raised in isolation but developed repertoires of 400+ bird song variations, without ever hearing adults mimicking. They did not care to imitate other lab catbirds’ songs, either, but personalized their performances. Furthermore, their songs were not atypical of the species even though composed in a laboratory cage. This was tested by recording them and playing them to wild catbirds in the country, who mobbed the speakers looking for rivals. That each lab bird sang differently backed up the reported lack of regional dialects among catbirds nation-wide. Scientific supposition is individualization of gray catbird mimicry is connected to males attracting a mate. Although both sexes sing, it is the males that have repertoires of hundreds of variations.
Another recently confirmed thing about catbirds is they are egg thieves. This was accidentally caught on video in 1998 by Mark Huber at Cornell. Huber wanted to tape the frequency cowbirds removed eggs from vacant nests and replaced them with eggs of their own. He wired several phony nests to limbs filled with plastic eggs. He found 87% of them had been raided by something, but that no cowbirds eggs had been substituted. Huber set up a video camera to watch one of the nests and, to his surprise, filmed two gray catbirds trying to eat the plastic eggs: “The recording showed that at 17:14 a Gray Catbird landed on a neighboring branch, erected its feathers, and approached the artificial nest. Within 20 seconds it grasped one of the eggs in its beak, lifting it from the nest, apparently trying to swallow it. It failed to do so and the egg fell to the ground (where it was later recovered). At 17:15 a second catbird arrived, hopped on the nest, and pecked into it six times, while the first bird moved away from the nest but remained within the camera’s field of view. After 15 seconds the first bird approached the nest again, displaced the second individual , and delivered 19 visibly powerful pecks at the eggs. It lifted one of the eggs up to the perimeter of the nest three times before finally flying off at 17:17.”
Egg predation by catbirds had been reported as far back as 1884. Arthur C. Bent mentioned it in 1948. Not many took is seriously until Huber caught it on film.
If there is a moral in this information it is that gray catbirds are a more complicated organism than bored banders generally suppose. The catbird tribe is idiosyncratic, with emphasis on song individualization. Other birds’ songs are just jumping-off spots for them to begin improvising. Although low-key, catbird song is based upon theme and variation rather than mimicry. And, catbirds are not above being scoundrels if opportunity brings a free meal.