SLENDER-BILLED NUTHATCH. Sitta carolinensis aculeata Cassin

Field characters.—Size nearly that of Junco; tail about half length of body. Top of head and back of neck black or slate-black; cheeks and under surface of body pure white back slate gray. (See pl. 10e). Runs about readily on bark of trees, moving in any direction. Voice: Song a series of double notes all alike, cher-wer; call note a nasal hank.

Occurrence.—Resident in Upper Sonoran Zone on west slope of Sierra Nevada where recorded from near Lagrange and Merced Falls eastward to Smith Creek, east of Coulterville; present in Transition and Canadian zones on west slope except during midwinter; also found east of mountains (Mono Mills) during summer season. Lives low on trunks and larger branches of both coniferous and broad-leaved trees. Solitary.

The Slender-billed Nuthatch is the largest of the three nuthatches found in the Yosemite region. Because it is fairly common and does its foraging chiefly on the lower parts of the trees, it is the species most likely to be seen.

The Slender-billed Nuthatch enjoys a wide distribution in the Yosemite section. It is resident in the blue-oak belt of the western foothills, and is found also, at least from spring until early winter, in the Transition and Canadian zones. Its range on the west slope extends from near Lagrange and Merced Falls eastward. The easternmost summer record was made at Mono Meadow, a few miles south of Glacier Point. In the early fall, as is shown by records from Ten Lakes, McGee Lake trail, and the Clouds Rest trail near Little Yosemite Valley, the birds invade the higher mountains. On the east slope of the mountains Slender-billed Nuthatches were found at Mono Mills on June 7 and 10, 1916, and at Williams Butte, Walker Lake, and Warren Fork of Leevining Creek, in the fall of 1915.

The three species of nuthatches of the Yosemite section agree closely not only in general form of bill, wings, and tail, but also in having bluish gray backs and in possessing white spots on the outer tail feathers. (See pl. 10e, f, g). There are, however, sharp differences between these birds, to be seen if looked for with some little care. The Slender-billed is about twice the size of the Red-breasted and Pigmy nuthatches and the entire side of its head or 'cheek' is white; the under surface of the body also is pure white. In the other two birds the side of the head at least down to the eye is dark, and the lower surface is not clear white. The adult male Slender-billed has the top of the head silky black, whereas in females this area is much duller. This difference in coloring affords a means for distinguishing the sexes in the field.

The word nuthatch comes to us from the Old World where it was first applied to a European relative of our birds which has the habit of wedging nuts into crevices and then hacking them open. Our nuthatches do considerable pounding with their bills both in digging their nest holes and in breaking up food materials. Nuthatches, creepers, and woodpeckers get most or all of their living on the trunks and branches of trees, but the representatives of each of these groups go after their food in different ways. The woodpeckers dig out grubs and insects which burrow in or beneath the bark, while the other birds mentioned get eggs, larvae, and adult insects which take shelter in the furrows in the bark. Probably the smaller sized nuthatches and creepers obtain, on the average, 'bugs' of smaller caliber than are sought out by the woodpeckers. The bill of the creeper is a more delicate instrument than that of the nuthatches. Its slender curved form makes possible to the bird a farther reach, into the narrowest of crevices where small insects lurk.

A creeper moves only upward on the trees, whereas the nuthatches run about without reference to direction, and go up, down, or crosswise seemingly with equal facility. The short tail of a nuthatch is always carried in line with its back and gives the bird no support such as the creeper obtains from its longer and stiff-pointed tail. The nuthatches have long toes provided with stout, well-curved and sharp-pointed claws, and these, catching in small irregularities in the bark, enable the birds to cling readily, whatever their position with reference to the pull of gravity. The bill is straight, rather strong, and sharply pointed, and serves equally well in pulling insects out of crevices, hacking open nuts or seeds, and in excavating or enlarging nesting holes in rotten wood.

Nuthatches usually keep rather closely to their distinctive mode of foraging; yet on one occasion, at Chinquapin, May 20, 1919, a Slender-billed Nuthatch was observed capturing flying insects. The bird was clinging 25 feet above the ground on the trunk of a tree, facing downward but with its head turned outward almost at right angles with the trunk. Upon sighting a passing insect the nuthatch would dart out, with undulating flight resembling that of a small woodpecker. Its tail was spread so that the marginal white spots showed plainly. With this short but broad 'rudder' the bird seemed to be able to change direction easily while pursuing its winged prey. Upon making a capture the nuthatch would alight upon some nearby tree, run along until an appropriate place was found and then, turning head downward, would pound the insect until it was in condition to swallow. Four or five perches within a 50-foot radius were occupied thus during the few minutes that this bird was under observation.

On the same date and at the same place another Slender-billed Nuthatch was watched as it foraged about the bases of the fir trees and on the ground. It seemed rather incongruous for this bark searcher to descend and cross the needle strewn earth between adjacent trees. The bird visited fifteen or so trees and fallen logs during as many minutes but seemed to have no fixed forage beat as these were not visited in any regular sequence. Rarely did the bird go far above the ground; its highest excursion was not over 15 feet. On the fallen logs it worked just as on standing trunks and if it disappeared from sight its travels soon carried it back into view again.

The voices of the three species of nuthatches are distinct. The call of the Slender-billed Nuthatch is a rather loud hank or quank, repeated at varying intervals. This call possesses somewhat of a nasal intonation but not so much of that quality as there is in the call of the Red-breasted Nuthatch. The Slender-billed never utters any high-pitched, clear, 'chattering' notes such as are given by the Pigmy Nuthatch. In the spring the Slender-billed Nuthatch gives a song which is a mere monotonous repetition of a certain two-syllabled word: cher-wer, cher-wer, cher-wer, etc.

The Slender-billed Nuthatch, at least in the Yosemite section, ordinarily makes use of abandoned woodpecker holes for nesting sites. In some other regions the birds are reported to dig out their own nest holes, but here they seemingly find sufficient accommodation in the numerous holes left by woodpeckers. Two instances of nesting were recorded at Tamarack Flat on May 25, 1919, and a third near Pleasant Valley on May 23, 1915. The first of the Tamarack Flat nests was 9 feet above the ground in an old hole of the White-headed Woodpecker in a broken off and barkless Jeffrey pine stump. The male bird was seen to enter with a bill full of insects and there ensued at once from the opening a series of low conversational notes. The contents of this nest were not ascertained. The second nest, also in an abandoned White-head's hole, was 7 feet (2130 millimeters) from the ground, measuring to the top of the hole. The entrance was as made by the woodpeckers (1-3/4 inches or 43 millimeters in diameter), but the interior had evidently been enlarged, by the nuthatches themselves, to a diameter of over 5 inches (130 mm.) and was filled to within 7-1/2 inches (190 mm.) of the top, with deer and chipmunk hair and feathers from various birds. There were seven slightly incubated eggs. The male kept uttering a special alarm call, yek-yek-yek ek-ek-ek, and circulated about the vicinity anxiously.

The female was on the nest and as she refused to leave even during the hubbub incident to enlarging the entrance, the observer had to lift her from the nest in order to examine the eggs. She seemed to be in a sort of lethargy and did not struggle until actually taken in hand. That the bird had not left the nest for some time was evident from the quantity of excrement which was accumulated in the cloaca. The condition of this female, the food supply which the male of the first nest had been seen to take to his nest, and the further fact that only males had been noted abroad for some days previously, led to the belief that in this species the female alone carries on the duties of incubation and that she remains upon the nest continuously for a greater or less period of time, during which she is fed by the male. In the case of the third nest, mentioned beyond as being seen in the foothill country, and which contained young, both of the parent birds were abroad, engaged in gathering food for the brood. These observations, added to our knowledge of other species of birds, indicate that only accurate observation of a species through the nesting season will establish the exact relations existing in that species between the sexes and between the adults and the young. It is unsafe to attempt to predict the behavior of one species from consideration of the known habits of other, even near-related, species.

Another nest of the Slender-billed Nuthatch was seen on May 23, 1915, in a dead blue oak near Piney Creek not far from Pleasant Valley. The two parent birds were busily engaged in capturing and carrying insects to the young. The presence of a member of our party 6 feet below the nest caused obvious anxiety upon the part of the two members of the pair who flew back and forth for twenty minutes before one of them became courageous enough to enter and feed the brood. Soon after the first had left, the other parent fed the young. Each again filled its bill full of insects, but neither would venture into the nest a second time; they flew back and forth uttering their curious little notes, and in so doing did not seem to find it necessary to open the bill at all.