33 



crow, catbird, black-billed cuckoo, yellow-billed cuckoo, yellow warbler 

 and chestnut-sided warbler. 



Those birds which not only eat hairy caterpillars but also feed them 

 to their young are doubly useful, because of the enormous amount of 

 insect food required by young birds. Our experiment shows that young 

 crows weighing fifteen and one-half to sixteen ounces require at least 

 ten ounces of food each day for their growth and development. Pro- 

 fessor Treadwell fed a young robin in twelve hours forty-one per cent 

 more than its own weight in worms. The same bird consumed nearly 

 half its own weight of beef in a day. 



Young birds must have animal food in order to grow and develop 

 rapidly, and this food consists mainly of insects. An idea of the con- 

 stant feeding required by the young may be gained from the following 

 brief account of the work of two pairs of birds during the greater part 

 of the day. 



On June 13, 1899, Mr. Mosher watched a pair of red-eyed vireos feed- 

 ing their young. There were three young about a clay old in the nest. 

 It was near the ground and the birds could be readily observed. The 

 observer did not reach the nest until nearly 7 a.m. (when the birds had 

 already been feeding their 3 r oung probably for at least two and one-half 

 hours) and left at 5 p.m., at which time the day's work was not finished, 

 so that this cannot be considered a complete record of the clay. Visits 

 were made by one or the other parent, — 



Between 7 and 8, 14 times. Between 12 and 1, 9 times. 



8 " 9, 9 " " 1 " 2, 12 " 



9 " 10, 12 " " 2 " 3, 15 " 



10 " 11, 7 " "3 " 4, 13 " 



11 " 12, 16 " " 4 " 5, 18 " 



making altogether 125 visits in ten hours. 



As these young birds were very small only a few insects were brought 

 each time, and most of those brought were so small that they could not 

 be positivel}- identified ; but caterpillars form a considerable part of the 

 food of these birds at this season. 



On June 12, 1899, Mr. Mosher watched the nest of a pair of rose- 

 breasted grosbeaks from early morning till 5 p.m. The nest was about 

 fifteen feet from the ground, in a slender white birch. The ground was 

 covered with hazel nut bushes, in which he found partial concealment, 

 but for the first half hour the old birds were so excited by his presence 

 that the feeding of the young birds was inteiTupted, so that no notes 

 were taken until 6 a.m., and none were taken after 5 p.m. 



The old birds visited the nest, — 



Between 6 and 7, 52 times. Between 12 and 1, 32 times. 



7 " 8,47 " " 1 " 2,38 " 



8 " 9,43 " " 2 " 3,41 " 



9 " 10, 30 " " 3 " 4, 22 " 



10 " 11,36 " " 4 " 5,58 " 



11 " 12, 27 " 



making altogether 436 visits during the portion of the day that they 

 were watched. The food was mainly caterpillars of one kind or another, 

 and there were onty four visits made by a parent bird when but one 

 insect was fed to the young ; they usually brought three or more. 

 Birds often carry in this way from three to eleven or twelve small 

 caterpillars in their mouths and beaks at one time. Owing to the 

 height of the nest above the ground it was impossible to determine 

 accurately the species of caterpillars brought to the young. A con- 

 siderable proportion of them were certainly leaf rollers from the oak 

 trees. It seems probable, then, that these two birds must have fed their 

 young on that day at least one thousand insects, mostly caterpillars. 

 This certainly is a very moderate estimate of the number of insects 



