Studies of Food and Growth of the Prairie Falcon

In the spring of 1928 the bird lover who has the regular annual job of "loving" the Prairie Falcons in one of the canons of the San Joaquin side of the Mount Hamilton range was either seriously sick, or in foreign parts, or forcibly confined by the police-therefore unable to perform his regular duties.The details do not greatly matter; the main thing is that two pairs of falcons hatched their eggs.The unique opportunity thus afforded to observe the young at progressive stages of their development was obviously not to be neglected.Nest number 1 was in the upper foothills, at an altitude of about 1700 feet.The eggs were laid on the loose rock chips and sand of a small shelf overhung by the upper part of a sandstone cliff.The distance from the top down to the shelf was about ten feet, and from the shelf to the base of the cliff about forty-five feet more.From the bottom of the rock a steep slope of earth pitched off into a gully.The nesting site faced to the south.Nest number 2. was in the lower foothills, at an altitude of about 800 feet.This nesting bluff also faced south, and was composed of conglomerate overlying soft sandstone.The eggs were laid in a slight depression in the sandstone, several feet back in a horizontal cleft formed by weathering along the plane of contact between the conglomerate and the sandstone base.The height from the base of the cliff to the nest level was about ten feet, but by working along from the end of the ledge, flat on one' s face under the overhanging conglomerate, the nest could be reached without a ladder.Higher on the bluff, and to the left, was a cavity occupied in 1928 by a pair of Horned Owls, apparently using an old raven' s nest; in 1930 this nest had again changed tenants, being occupied by another pair of falcons that were photographed from a blind suspended on cables.This nest of 1930 is designated nest number 3, in the note on page 201 of this article.On April 1, 1928, inspection through glasses from the opposite hill showed at least four and probably five eggs in nest number 1. On the same day a full set of five eggs was counted in nest number 2.On April 15, both sets were found to be still intact, and on going over the cliff to take photographs it was definitely ascertained that nest 1 contained five eggs.A business trip delayed the next examination of nest number 1 until April 29, when it was found to contain five young falcons, about nine days old, according to subsequent weight comparisons.Nest number 2, which could not be visited until May 6, then contained four very young birds, believed, after much subsequenr study and figuring, to average about three days old.They were weak, had a marked tendency to capsize, and when they did roll over immediately curled up as if still in the shell.Only the most advanced had their eyes part way open, and the others showed very marked and extensive granulation around the unopened eyelids.No remnants of the fifth egg, nor of any chick hatched from it, could be found.The young in nest number 1 were systematically weighed and photographed in the nest, until the family took to wing some time between May 23 and the next visit on May 30.Those in nest number 2 were weighed, and a selected bird photographed to scale, until they appeared ready to leave the nest when last visited June 6.