YELLOW-HEADED BLACKBIRD 109 



were no yearling males in either colony, but plenty of them were seen 

 in the surrounding regions. 



Young. — In another excellent paper, Fautin deals with the devel- 

 opment of young yellow-headed blackbirds. Both studies were 

 conducted in the same two colonies, near Provo, Utah, during the 

 spring and summer of 1937, from April to September, some 128 nests 

 being kept under observation. He (1914a) found that: "The average 

 weight of the nestlings at the time of hatching was 3.3 grams and at 

 10 days of age was 51 grams; the greatest percentage of increase in 

 weight occurred during the first day after hatching, while the greatest 

 actual increase in body weight occurred between the fifth and sixth 

 days, amounting to 6 grams at that time." He noticed that nestlings 

 of the same age varied as much as 15 to 20 grams in weight at the 

 time of leaving the nest, though the smaller ones were as well feathered 

 and as active as the larger ones; inasmuch as adult males are much 

 larger than females, averaging about 35 grams heavier, it is likely 

 that the larger nestlings were males. 



Feather development began soon after hatching; the sheaths of the primaries 

 appeared the second day. At eight to nine days of age the contour feathers were 

 sufficiently developed to cover all the apteria except possibly the one on the 

 abdomen. 



The males aid very little in caring for the nestlings. Only two males were 



observed to make any attempt to feed the young. One of these fed the young 



eight times during a period of eight hours and six minutes while the female fed 



them 102 times during the same interval. The other male fed another brood of 



nestlings eight times while the female fed them 92 times during the same period. 

 * * * 



Food of the nestlings consisted principally of insects and spiders. The spiders 

 and smaller insects constituted the greater part of the diet during the first few 

 days after hatching, while larger insects such as dragonfiies and grasshoppers 

 together with some vegetable matter formed the bulk of the food as the young 

 became older. * * * For the first day or two after the young are hatched they 

 are fed either by regurgitation or else on food materials so small that they escaped 

 notice, for during that time the females were seldom seeu carrying food in their 

 mouths although the young were visited six to seven times per hour. Probably 

 they were fed by regurgitation during that time. * * * 



The nestlings left the nests w T hen nine to twelve days of age and remained 

 among the dense vegetation of the nesting area until they were able to fly. * * * 

 The young are unable to fly at the time they leave the nest but they are very adept 

 at making their way through the vegetation. After abandoning the nest they 

 never return to it but are to be found among the vegetation down near the surface 

 of the water, sometimes sitting on the dead floating vegetation. * * * For the 

 first four or five days they move about by hopping from one stem or leaf to another 

 with remarkable agility. Following this hopping stage they make short flights 

 of about two to four feet and thus gradually develop their ability to fly. By the 

 time they are three weeks old they are frequently seen to make short flights of 

 about 25 yards. From this stage on, their ability to fly develops very rapidly 

 and they are soon seen pursuing their parents, coaxing noisily for food." 



