27 



along the swollen streams the lusty fox sparrow searches for hibernating 

 insects, which only await the warmer sun of April or May to emerge 

 from their hiding places and lay their eggs upon or attack the trees, 

 lie and his companions, the tree sparrow and the junco. soon pass on to 

 the north, making way for the white-throats and thrushes, winch con- 

 tinue the good work, to he followed in their turn by other thrushes and 

 towhees. In early April birds are not plentiful in the woods, but the 

 chickadees, woodpeckers, jays, nuthatches and kinglets are doing their 

 part. Later, in the warm days of May, when nature has awakened from 

 her long winter's sleep, when the little, light green oak leaves are just 

 opening, when the bright young birch leaves decorate but do not hide 

 the twigs, when every leatlet vies with the flowers in beauty and every 

 branch upholds its grateful offering, when insects which were dormant 

 or sluggish during the earlier days of the year become active in ascend- 

 ing the trees, and when their swarming offspring appear on bud and 

 leaf, then the south wind brings the migratory host of birds which 

 winter near the equator. They sweep through the woods, they encom- 

 pass the trees, flight after flight passes along on its way to the north, all 

 gleaning insects as they go. No one who has not watched these birds 

 hour after hour and day after day, who has not listened to their multi- 

 tudinous notes as night after night they have passed overhead, can 

 realize the numbers that sweep through the woods in the spring and fall 

 migrations. Those who have watched the flights of wood warblers 

 during the present season cannot but marvel at their vast and constantly 

 changing procession. On May 11 of the present year at Amesbury, 

 Mass., Blackburnian warblers were seen all through the woods at day- 

 break. Having come in the previous night they were not singing but 

 were busily feeding until seven o'clock. At eight o'clock not one was 

 to be seen. They had passed on, and other species had taken their 

 place. 



The great body of migratory warblers feeds largely on caterpillars 

 and plant lice, — two of the worst enemies of trees. They come at a 

 time when the first broods of these creatures appear, and so do yeoman 

 service in preventing their enormous increase. One needs only to know 

 the possibilities in the vrny of reproduction among the plant lice to ap- 

 preciate the services of birds in destroying these early broods. Lintner 

 says of one species, — the hop-vine aphis,— that according to Riley 

 it has thirteen generations a year, and that, giving the average number 

 of young produced by each female as 100, if every individual should 

 attain maturity and produce its full complement of young, the twelfth 

 brood alone would amount to ten sextillions. If this brood, says Lint- 

 ner, were marshalled in line, ten to the inch, touching one another, the 

 procession would extend to the sun (a space travelled by light in eight 

 minutes), and beyond that to the nearest fixed star (a distance travelled 

 by light in six years), and onward into space beyond the most distant 

 star that the strongest telescope may bring to our view, to a point so 

 inconceivably remote that light would only reach us from it in twenty- 

 five hundred years. It need hardly be said that no such multiplication 

 as this can ever occur in nature, still the calculation shows the possibili- 

 ties of great danger to vegetation should any of the forces be withdrawn 

 which hold these insects in check. Dr. Fitch, by a careful enumeration 

 and computation, estimated that several young cherry trees about ten 

 feet in height were each infested by at least twelve millions of aphids.* 



The increase of these creatures is largely controlled by birds, but in 

 greenhouses, where birds cannot go, plant lice are a serious evil, and 

 florists have to combat them with insecticides and fumigation. The 

 value of birds as aphis eaters has been shown by confining birds in 

 greenhouses. E. A. Samuels savs that three full-grown rose bushes in 



* American Journal Agricultural Science, 1846, page 282. 



