960 



SCIENCE 



[N. S. Vol. XXXII. No. 835 



and sometimes recorded elsewhere, especially 

 further eastward through Illinois, Indiana, 

 Ohio and Michigan. 



A rough estimate of the numher of birds 

 passing a given point in a spring may be 

 useful. The cross-section of an average flock 

 was, say, a hundred yards from front to rear, 

 and fifty yards in height, and when the birds 

 were so close as to cast a continuous shadow 

 there must have been fully one pigeon per 

 cubic yard of space, or 5,000 to each linear 

 yard of east-west extension — i. e., 8,800,000 to 

 the mile, or (with reasonable allowance for 

 the occasional thinning of the flock) say 30,- 

 000,000 for a flock extending from one wood- 

 land to the other. Since such flocks passed 

 repeatedly during the greater part of the day 

 of chief flight at intervals of a few minutes, 

 the aggregate number of birds must have ap- 

 proached 120,000,000 an hour for, say, five 

 hours, or six hundred million pigeons virtu- 

 ally visible from a single point in the culmi- 

 nating part of a single typical migration. 



While the passenger pigeon migrated an- 

 nually and in vast numbers over eastern 

 Iowa, far exceeding the aggregate of all other 

 migratory birds and water fowl combined, 

 there was an irregularity of movement sug- 

 gesting absence of a definite and long-estab- 

 lished migratory habit such as that, e. g., of 

 the water fowl passing the same point. In 

 the first place the migration was not well ad- 

 justed to the season : Frequently the pigeon 

 was the first migrant to appear, arriving 

 sometimes after one or two . warm days of 

 southerly wind while yet the snow remained, 

 so that they were liable to be caught by cold 

 and storms; while geese, cranes and various 

 ducks came generally later (though some- 

 times earlier) when the season was so settled 

 that they rarely, if ever, suffered from cold, 

 old snow and ice, or belated storms. In the 

 second place the pigeon flocks seemed wholly 

 unorganized. Unlike the geese and cranes 

 and most of the ducks, which flew in oblique 

 lines or Vs following a leader and on alight- 

 ing kept sentinels on guard, the pigeon flocks 

 were without visible leadership, the multitude 

 merely hurrying forward with the stronger 



flyers toward the front, but constantly inter- 

 changing position, and when they alighted on 

 trees and then flew down to forage on the 

 ground each bird apparently moved according 

 to its individual caprice, and no sentinels 

 were left save by chance; the entire flight of 

 the day, if not of the season, seemed to be 

 that of a promiscuous horde of individuals, 

 fortuitously broken up, as it were, into a 

 series of successive waves in which each bird 

 sought merely to remain near the others, 

 veering to the right or left rather than forg- 

 ing to the front if of superior strength, in 

 such manner as to extend the flock laterally 

 rather than in the line of flight — apparently 

 the smaller flocks appearing toward the end 

 of migration were of birds left behind either 

 by belated start or because of inferior 

 strength, and being unequal in freshness or 

 power of flight they strung out longitudi- 

 nally rather than spreading laterally like the 

 more numerous and more vigorous flyers. 

 Again, unlike the water fowl which returned 

 southward in the autumn in larger numbers 

 than in the spring flight, the pigeons had no 

 autumnal migration; about September and 

 October they were a little more numerous 

 than during the summer, and might occasion- 

 ally be seen in twos, threes, fours or rarely in 

 larger groups flying southward rather irregu- 

 larly; but there was no general return of the 

 vast hordes moving northward in the spring 

 — it was as if the excess of birds annually 

 went out to their destruction as the Nor- 

 wegian lemming are said occasionally to rush 

 to their death in the sea. Like the water 

 fowl, the pigeons undoubtedly nested and bred 

 in the north, though their chief breeding 

 grounds must have been in the south, whence 

 the vast flocks moved northward with the ad- 

 vent of spring, apparently in a desperate food- 

 quest which might or might not be successful. 

 Most records of the passenger pigeon note 

 the flight of the flocks and perhaps the col- 

 lective nesting, but not the scattered breeding 

 within the zone covered by the migration. In 

 eastern Iowa individual pigeons left the vernal 

 flocks in considerable numbers and remained 

 to pair, nest and produce young — the number 



