The Condor/Volume 9/Number 2/Nesting of the Sierra Creeper
Nesting of the Sierra Creeper.—During the summers of 1905 and 1906 spent in the San Bernardino Mountains of southern California, I became acquainted with the nesting of the Sierra creeper (Certhia americana zelotes). The species proved to be more numerous than I have ever seen it elsewhere, in the upper part of the Santa Ana Canyon and on its tributaries and adjacent slopes. While observed from an altitude of 5600 feet in the Santa Ana Canyon to as high as 9500 feet, above Dry Lake, on the north base of San Gorgonio Peak, yet the creepers were most abundantly represented in the canyons from 6000 feet to 7500 feet. This belt of abundance was also the belt in the Transition Zone where the incense cedar (Libocedrus decurrens) is conspicuously represented. And it was in these cedars that the majority of the creepers' nests were found.
While the birds themselves were most often seen and heard high above, scaling the massive trunks of the huge firs, pines, and cedars, yet their nests ranged not higher than twenty feet above the ground. Myself and companions examined fully thirty nests, easily discovered after we once learned how to find them, and of these I should judge the average height to have been six feet. In other words the majority could be at least touched by the band as we stood on the ground. One nest was only three feet above ground.
Altho the majority of the nests found were on cedar trunks, one was on a Jeffrey pine, and at least five were on silver firs. In the latter cases the trees were dead and rotting, for it was only on dead trees that the bark had become loosened and separated enough from the trunk to afford the narrow sheltered spaces sought by the creepers for nesting sites. But the huge living cedar trunks furnished the ideal situations. For the bark on these is longitudinally ridged and fibrous, and it frequently becomes split into inner and outer layers, the latter hanging in broad loose strips. The narrow spaces behind these necessitate a very compressed style of nest. A typical nest closely studied by me may be described as follows:
The material employed externally was cedar bark strips one-eighth to one-half inch in width. This material had been deposited behind the loosened bark until it packed tightly enough to afford support for the nest proper. The bark strips extended down fully a foot in the cavity, and some of them protruded thru the vertical slit which served the birds as an entrance. The main mass of the nest consisted of shredded weathered, inner bark strips of the willow, felted finest internally, where admixed with a few small down-feathers. This nest proper was six inches wide in the direction permitted by the space, and only one and three-fourths inches across the narrow way. The nest-cavity was one and one-third by two and one-fourth inches, so that the sitting parent probably always occupied one position diametrically.
No nests were found with eggs later than June 11, but young were found, yet unable to fly, until July 20. Two sets of eggs found on June 11 consisted of four and five eggs, respectively. Broods of young were of three to six individuals, one of the latter number being noted on June 26.
The ground-color of the eggs is pure white. The markings are elongated in shape lengthwise of the egg. The brightest markings are burnt sienna the tint varying from this towards vinaceous as the depth of the markings in the shell-substance increases. The darkest markings average one millimeter in diameter, while the vinaceous ones vary down to mere points. The markings are most crowded around the large ends of the egg-shells, and radiate from this pole in lesser numbers towards the opposite pole. The nine eggs are quite uniform in appearance, tho certain ones are to be distinguished as more sparsely, more boldly, or more minutely marked. The markings on one set are not so dark as on the other, approaching pale hazel at darkest and ranging to vinaceous-cinnamon.
In shape the eggs of the Sierra creeper vary from ovate to elliptical-ovate. The two sets measure, in hundredths of an inch: .61x.45, .63x.42, .61x.44, .60x.44 and .56x.43, .57x.44, .59x44, .55x.43, .58x43.—Joseph Grinnell, Pasadena, California.