I have a window above my kitchen sink where I gaze outside several times each day. Watching birds entertains me during kitchen chores, and makes me feel like I am spending time outdoors – which is my favorite place to be.
One warm, sunny day I saw a crow squatting low on a large ant hill, head high, wingtips outstretched and fluttering softly on the ground. I had never seen this behavior before and I wondered if she might be injured. I watched her with concern before she stood up, briefly picked at her feathers, and flew away.
I’ve seen birds take dust baths and water baths – could this be a similar behavior? Flickers are frequently on the ant hill, but they are obviously at the dinner table and this crow was not eating. A few days later I witnessed it again. Several other crows were walking around and watching her, but she would peck at any curious crow that got too close. Now my curiosity was piqued and I wanted to know more.
I discovered this behavior is called anting, and over 200 species of birds practice it. There are two types. “Active” anting is when the bird picks up an ant in its beak and rubs it on its feathers. “Passive” anting, which is what I witnessed, occurs when the bird settles in and lets ants crawl through its feathers. They both accomplish the same thing. The bird’s feathers become saturated with formic acid which the ants spray from a gland at the tip of their abdomen. Crows use the passive type of anting almost exclusively.
Ants from the subfamily Formicinae produce and spray the chemical for defense, to attack, and to mark trails. The crow was purposely provoking the ants to spray her feathers. Why would this be a good thing? There are several hypotheses, such as reducing skin irritation from molting feathers, or it might just feel good. However, one hypothesis stands out to me.
Birds have to combat a variety of ectoparasites such as lice, mites, fungi, and bacteria that can damage feathers and can weaken them. There are many ways birds do this. Preening is the most important and common. They also engage in scratching, sunning, dust baths, water baths, and allopreening (preening each other in hard-to-reach spots like the head and neck). Some scientists believe birds might use anting to help keep their plumage free of these pests. The acid irritates the lice and mites, so they move out from between the feather barbs and are easier to reach with preening and scratching. It can also kill the parasites.
After discovering the potential benefits to birds, I wondered if I could learn more from researching the ants. A recent study showed that ants will use formic acid like a fungicide, gathering their own formic acid with their antennae and cleaning food they bring to the nest. They also consume this acid, which increases the acidity in their stomach and kills bacteria. Since ants live and work cooperatively in close quarters, these strategies help them keep their nest clean.
For me, this reinforces the idea that anting reduces a bird’s ectoparasites. But it also makes sense that birds would have more than one reason for engaging in this behavior, as nature is rarely so cut and dried. I love seeing yet another example of how creatures on our beautiful blue planet are unexpectedly interconnected.
I am thankful to the backyard crow for inspiring me to learn more about her world, and I relish my good fortune, for I have a window.
Today’s Field Note was written by Jill Weigel in the Field Notes Writing Workshop at the Montana Natural History Center. I’m Allison De Jong for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. To find out about upcoming events and programs at the Center, call 406.327.0405, or visit our website at MontanaNaturalist.org.