Home & Garden Columns

Wild Neighbors: When One Bird’s Nest is Another’s Home Depot

By Joe Eaton
Tuesday June 26, 2007

It began with a phone call: Jean Moss, a Berkeley reader, had an odd nest that had fallen from a Cecile Bruner rosebush. She suspected it was some kind of hummingbird nest, because she had seen a female hummer hanging around it acting territorial. But what she described sounded more like a bushtit nest, bag-shaped with a small entrance hole near the top. Curious, I arranged to stop by and take a look at it. 

Bushtit is what it was, all right, very much like the one I discovered last year in the Lady Banks rose outside the kitchen window. It was a remarkable object, tightly felted from plant matter and spiderweb and decorated with moss and lichen. According to Hal Harrison’s Field Guide to Western Bird Nests, bushtits may also use leaves, grasses, and cocoons for the basic construction and plant down, wool, hair, and feathers for the lining. 

Mrs. Moss was adamant that she hadn’t seen any bushtits—chubby long-tailed grayish birds—in the neighborhood, and I am convinced she knows a bushtit from a hummingbird. So what about the hummer? I have a theory about that, and I’ll get to it later. 

Bushtits are interesting little birds, though. (I don’t know who saddled them with that name.) Once thought to be close relatives of the chickadees and titmice, the last taxonomic reshuffle put them in a separate family along with the Eurasian long-tailed tits, and recent studies suggest they may be close to the Old World warblers. They got here some 10 to 12 million years ago, via the Bering land bridge, and have spread as far south as Guatemala. 

They’re even more social than chickadees. You hardly even see a lone bushtit. Except for the nesting season, flocks stick together year-round, and pairs rejoin the flock as soon as their nestlings fledge. Flock members roost together, huddling close for warmth on chilly nights. They forage as a group, bridging the gaps between trees one bird at a time. 

In some parts of their range, bushtit sociality goes even farther: two or more females may lay their eggs in the same nest, and supernumerary helpers—maybe last year’s offspring—help the parents rear the brood. But this seems more common in southern Arizona than in coastal California. 

There seem to be two basic nest-building techniques. In heavy vegetation, the pair attaches spiderweb and plant material to a couple of support points and stretches the incipient nest into a loose sack. Alternatively, they start with a platform bridging a fork in a branch. One or both of the builders stretches the platform into a cup by sitting in it. Eventually the cup becomes a sack. I couldn’t track it down, but I recall reading somewhere about some northern people—the Saami, or some Siberian tribe—using the nests of long-tailed tits as children’s footwear. 

Like many Bay Area resident birds, bushtits start their nesting season early; eggs have been confirmed in California nests as early as February 26. Some coastal California populations raise two broods a year.  

So it’s reasonable that a bushtit nest should be active in May. But how to account for the hummingbird? Some birds do reuse the nests of other species; the piratic flycatcher of the New World tropics boots the original owners out and takes their nest over. But I could find no account of our local hummers using another bird’s nest. Their own open-faced cup-shaped nests are completely different in size and shape; all they have in common is the decorative lichen. 

Huh. Lichen. Instead of nesting in the bushtits’ construction, maybe Mrs. Moss’s hummer was recycling it—using its components to build her own nest. That wouldn’t be unheard-of. Bushtits are known to steal nest material from each other, and in the Chiracahua Mountains of Arizona warblers and vireos dismantle bushtit nests for material. As for the hummer’s behavior, she might have seen the nest as a resource to be defended, like a patch of nectar-bearing flowers. 

Who knows? Birds do go to extremes to get their nesting material. I’ve seen lichen-covered hummingbird nests a long way from the nearest lichen. The grand prize would have to go to the South American fork-tailed palm swift, which lines its nest with feathers. It was assumed for a long time that it just picked up feathers that were lying around. But no. Recent observations indicate it plucks the feathers from the backs of other birds, in flight. Victims range in size from thrush to turkey vulture, but the swifts seem to have a preference for pigeon and parrot feathers. Must be an unsettling experience for the donors. 



Photograph by Joe Eaton. The mystery nest, with a pair of binoculars for scale. 


Joe Eaton’s “Wild Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Ron Sullivan’s “Green Neighbors” column on East Bay trees.