The Bridgeport evening farmer., 1915-04-12
WHY DO BIRDS
 MIGRATE?
No Such General Migration of Birds in South America As I'm Our
 Continent.

Continent.
 Washington. April 12-Although North American birds living II the colder part of the continent return South for the winter, there is no sinf- lar movement of birds from the cild- CT to the warmer paEts of South America according to a bulletin (11o. 185) of the United States Depart ment of Agriculture. If the birds in North America did not go South during the winter, they would per- isR Also if the birds remained in the South later than spring. there would be overcrowding; so they are drawn noEthward again by the enor- nous supply of bird food. Nm South America. on the contrary, there are almost no migratory land birds, be- cause the south. temperate attitudes. on account of their small area, offer no such Inducements to the feather ed inhabitants of the HnitIess forests along the Amaxons
 The new pamphlet. which is en- titled Bird ld1gratien.'' gives much Information regarding the habits of the migratory birds of North Ameri- lea The fact that the routes Of mi grafton are long and complex does not mean that these routes were so lin the beginning, says the bulletin I1s~t17e early ages. flight was probably short, easily accomplished, and com paratively free from danger. Each lengthenfng of the course was adopt- ed permanently only after experience through many generations had prov ed its advantage.
 There are some who argue that love of birthplace is the impulse which causes spring migration. and these call attention to tl1is seeming inpa- tiencey of the earliest arrivals. Ducks and geese push northward with the beginning of open water so early, so far, and lo fast. that many are caught by late storms and wamders diecon- sola4eIy over frozen ponds and rivers, rrs3 s3erxfmrr to rfBk starvation rather than to retreat The purpae mar tins ofsen awrive. at their nesting bomes so prematuFe4y that the cozy nome becomes a tomb if sleet storm sweeps their winged food from the air. The b1uebird's cheery war ble we welcome as a hamburger od spring, often only to find later life less body in some shed or outbuild- 1 ing where the bird sought shelter l rather than return to the sunny land so recently left.
 l As a matter of fact. however. only a small percentage of birds exhibit these preseasonal migration propen. slties The great majority remain 1T } the security of their winter homes un- til spring is so far advsnced that thf l journey can be made easily and wftF comparatively slight danger; and they reach the nesting spot when a food i supply is assured and all the condi tions of weather and vegetation art | iRf the rearing of a. family. 2
 Breeding Instinct Governs Return I It may be safely stated that tn, I weather in the winter homo ha l nothing to do with starting birds or I the spring migration, except in tn case of a few. like some of the duck and geese. which press northward al fast as open water appears. Ther' is no apprecfab1e change in tenpera l t1re Nfo warn hundreds Of species Q our birds which visit South Ameri ca in winter that 1t is time to mi grate. It must be 8 force from with in, a physiological change warnin, 9 them of the approach Of the breedini season, that iInpe1e them to sprea' their wings for the long flight.
 Thed habit of migration has beel evolved through counties generations T and during thts the physical structur and habits of birds have been under
 going a process of evolution in adap
 tation to the climate of the sun4me homes. In spring and early sE1nSme climatic conditions are decidedly var iable and yet there must be som
 period that has on the average tn best weather for the birds ariva. In the course of ages there have bee
 developed habits of migration. unde the influence of which the bird s
 performs it's migratory movement
 that on the average it arrives at tn nesting site at the proper time.
 Local Weather Conditions Minor
 Factors
 Local weather conditions on the da
 of arrival at any stated locality ar
 minor factors in determining the al
 pearance of a given species at ths place and time. The major factor g in the problem are the weather cond . tions far to the so1thward, where tt
 nights flight began, and the rsiatic
 which that place and time bear to tt
 average position of the bird undt
 normal weather conditions Many
 not most; instances of arrivals birds under adverse weather cond
 tions are probably explainable by u
 suppositton that the flight begun ul
 der favorable auspices and that lat
 the weather changed. Migration spring usually occurs with a risi1
 temperature and in thea utumn wi 4 a falling temperature. Tn each ca