Home & Garden Columns
Talk about your misperceptions: for years, I thought the California towhees in my yard were having boundary issues. Two towhees would fly toward each other, one or both uttering a loud squealing call that was nothing like their normal “chip” or “tsip.” It sure sounded like fighting words. The towhees would appear to confront each other with fluffed-out feathers. Then they’d break off and go back to scuffling through the leaf litter for bugs.
But it turns out this was not an exchange of invective but a duet performed by a mated pair: the towhee equivalent of “Oh June, I’m home!” “In here, Ward!” The California towhee and its close relatives, the Abert’s towhee and canyon towhee, are among the few known duetting North American birds (others include the wrentit, pygmy nuthatch, and northern cardinal.)
If you have an older field guide, you may still think of this bird as the brown towhee. That name was discarded in the 1990s when biologists discovered that the two populations included in the species—one coastal, one interior—were not each other’s closest relatives. Coastal brown towhees became California towhees; interior ones, canyon towhees. The two forms look different, behave differently, don’t hybridize, and in short seem to be distinct species (except for that odd population in southern Baja California; but let’s not get started on that).
Anyway, North America is poor in duetting birds, compared with the New World tropics, Africa, and Australia. Some of the tropical duetters’ performances are remarkable exercises in vocal coordination, sounding like a single bird’s performance. Our towhees don’t carry it that far: their squeal duets overlap rather than synchronize.
Just why birds do this has been a matter of some debate. UC-Berkeley graduate student Lauryn Benedict, whose dissertation work involves California towhee vocalizations, says there are a number of competing hypotheses. Duets used to be explained as a way of reinforcing the pair bond: “making the mate happy.” But a less anthropomorphic view would look at the costs and benefits of the behavior for each member of the pair.
What we know, thanks to earlier studies by Charles Quaintance and Joe T. Marshall, Jr., is that California towhees are sedentary birds that appear to pair for life. Benedict says several of the pairs she observes at UC’s Hastings Reservation in the Carmel Valley have been together for the length of her five-year study. Their vocalizations have been well documented, although it’s still not clear whether they’re learned, as in Luis Baptista’s famous white-crowned sparrows, or innate.
In some other birds, song duets have been interpreted as mate surveillance—the male making sure of his mate’s whereabouts at all times, so she can’t get together with any rivals who may be lurking around the territory. If this works, the male would not wind up helping rear nestlings sired by someone else. “All the other duetting species that have had their genetics done have been genetically monogamous as well as socially monogamous,” Benedict says. Her data on towhee genetics are awaiting publication, so she couldn’t discuss her findings.
The California towhee’s regular “chip” seems to function effectively enough as a contact/location call, though. A couple of years back a towhee got into our house through the open back door. It flew from room to room as if looking for an exit, chipping all the while. Meanwhile a second towhee, presumably the mate of the first, was chipping outside. The inside bird appeared to follow the outside bird’s chips into the bathroom and out the window into the plum tree where its partner had been calling.
Or what seems like cooperative behavior may really reflect a conflict between mates. “Maybe,” says Benedict, “the female sings and then the male sings on top of her song to signal that she already has a mate.” But the squeal duet is very different from the male towhee’s mate-attracting song, which is basically a sequence of chips. (He sings until he finds a mate, then shuts up for the rest of the season. Instead of territorial song, he makes a pre-dawn circuit of the perimeter of his domain, chipping away. Territorial males will also attack their reflections in windows, hubcaps, or bumpers.)
Duets may also signal the strength of a towhee’s commitment to its mate, or its general health and fitness—although the latter seems less likely for towhees then for the part-singing tropical birds. They may be a way for mates to coordinate their behavior: feeding their chicks or defending their territory. In territorial conflicts, two duetting birds can produce a stronger signal than one (and duets sometimes occur during clashes between neighboring pairs).
“When they duet, they always approach each other,” Benedict continues. “They do seem to be signaling something to each other.”
When her articles, now under review by The Auk and other journals, see print, we’ll have a better idea of what it’s all about. Stay tuned!
Photograph by Ron Story.
A California towhee, the bird formerly known as the brown towhee.