Window on Nature
By Lowell & Kaye Christie, F47246
We expect to see hungry birds snag their meaty morsels while flying, when picking through tree foliage, or by scrabbling on the ground. However, the four species of North American nuthatches gather part or all of their sustenance while clinging to a tree trunk “” usually upside down. The white-breasted nuthatch and the red-breasted nuthatch are the easiest to see. They hang right before one’s eyes.
The white-breasted nuthatch searches out its edibles by landing on a tree trunk head down. Then it slowly hitches and shuffles downward, pausing frequently to peck at the bark and uncover insects and larvae in the spaces that other up-climbing, tree-foraging birds miss.
Red-breasted nuthatches will creep in any direction for their meal “” up, down, or spiraling around. They aren’t limited to tree-trunk gleaning either; they are quite happy with morsels found while searching the branches or flying insects snatched from the air.
The other North American nuthatch relatives, the brown-headed nuthatch and the pygmy nuthatch, also work tree branches as well as trunks. Brown-headed nuthatches seem to prefer scavenging in pines, far up in the treetops and at the ends of branches. The well-named pygmy nuthatch isn’t a slacker either “” this tiny bird is so agile that it can sometimes feed while dangling upside down.
Clearly, all four species of North American nuthatches (there are 24 species worldwide) must be specially adapted to feed the way they do. For example, they need strong, sharp bills to pry off pieces of tree bark, and they must be very quick to grab the bugs hidden inside. And they couldn’t cling to tree trunks or hang from tree branches without short legs and feet equipped with sharp hooks on their toes.
Brown-headed nuthatches have the distinction of being the only North American bird that regularly uses a tool during foraging. Instead of abusing its bill, this tiny bird grasps a piece of bark (its tool) in its bill and uses it to pry up bits of tree bark and expose the insects underneath. Typically, the bird chooses a new tool for each effort, but it occasionally reuses the same tool many times. Scientists have photographed brown-headed nuthatches carrying their tool along with them and using it while foraging in several trees.
Nuthatches are cavity nesters. They will sometimes chisel out their own holes in dead trees, but they’re more likely to claim vacant woodpecker holes; adapt holes in stumps, posts, or utility poles; or use man-made bird boxes. It’s what they do at those nest sites that grabs your attention.
Once it has chosen a nest site, the white-breasted nuthatch engages in “bill sweeping.” The bird holds an insect, a tuft of fur, or some plant matter in its bill and then sweeps its head back and forth until it has marked the entire nest entrance. The operation may last for several minutes. It’s assumed that this sweeping masks the bird’s scent from predators and helps keep them from robbing the nest.
Red-breasted nuthatches have their own method of preventing predation. After locating a tree branch oozing sap, the bird carries mouthfuls of the pitch to its nest site and smears it around the nest hole. From that time on, until the eggs are laid, the chicks hatched, and the youngsters fledged, the parent birds fly straight into their nest without touching its exterior. In effect, they have created a sticky front porch for any predators who might happen by.
Brown-headed nuthatches don’t take particular precautions against predators, but they do caulk their nests to keep out drafts. Some, but not all, brown-headed nuthatches gather tufts of cotton or other plant down and use it to stuff the cracks and crevices of their nest cavities. Very clever “” but other nuthatch-watchers say pygmy nuthatches do a far better job of insulating.
Once while we were camping at Arizona’s Sunset Crater Volcano National Monument and enjoying “” what else “” the sunsets, a park ranger strolled over. During the conversation he told us about his research project “” studying the sleeping arrangements of pygmy nuthatches.
The ranger said he had verified that, when the weather is especially chilly, a group of these minute birds sleep piled one on top of another in a woodpecker hole. He recounted the experience of finding a chamber filled with more than two dozen birds. “But don’t the birds on the bottom smother?” we asked. The ranger admitted that while this was rare, it did sometimes occur. But more commonly, he said, the birds on the bottom start squirming and pushing upward when they need fresh air “” all part of a cycle in which the bottom layer of birds eventually rises to the top of the pile, and the well-aerated birds gradually (but not actively) settle toward the bottom.