Comparative Studies in the Growth of Young Raptores

During the year 1927 I had under my observation one nest each of the Golden Eagle (Aquila chrysaetos) and the Southern California Screech Owl (Otus asio quercinus).The young birds were weighed and photographed at regular intervals, and notes were taken regarding their general development.Several facts of particular interest were observed, chief among them being an actual loss of weight suffered by every bird without exception just before leaving the nest.Accordingly, during 1928, I have undertaken a more extended series of observations, with the view to verifying thase results, of which the present paper is a brief summary.The species whose nests have been visited are as follows : Cooper Hawk (Accipiter cooperii), one nest; Western Red-tailed Hawk (Buteo borealis calm-us), two nests; Golden Eagle, same nest on two successive seasons; Desert Sparrow Hawk (Falco sparoerius phalaena), one nest; Barn Owl (Tyto dba pratincoh), two nests; Longeared Owl (Asia wilsonianus), one nest; Southern California Screech Owl, same nest on two successive seasons ; Pacific Horned Owl (Bubo oirginianus pacificus), two nests.In order to avoid unnecessary repetition only one brood will be considered for each species, except for those few cases where the other brood has presented features not observed in the first.COOPER HAWK April 21, 1928.The female flushed from six fresh eggs and was immediately COOPER HAWK April 21, 1928.The female flushed from six fresh eggs and was immediately joined by the male.Both birds were bold, darting under the trees and perching within thirty feet of me while they continually uttered their high-pitched scolding cry.The nest is thirty feet up in an oak tree (Quercus agrifolia), and is composed of oak twigs and small sticks.The lining is entirely of twigs arid pieces of oak bark, with no sign of leaf or dry grass, giving the nest a peculiarly dean and dry appearance.May 14. Actions of parents as before.Four young have hatched.They whimper softly, and at the approach of my finger open their*beaks and redouble their cries.Eyes open, iris brown.Upper mandible black; lower mandible flesh color, becoming lighter at the tip; "egg tooth" present.Claws and feet flesh color.Total length about 88 mm.