Page:The Scientific Monthly vol. 3.djvu/237

 INSECT MIGRATION 231.

the beautiful Libelhda piilchella and the uncommon Tramea lacerdta. And, as both of these species (as well as Libellula semifasciaia) have been seen by the writer in extensive autumnal migration on Long Island, it is possible that both of these species, as well, follow the two great eastern routes already defined for the " monarchs."

Indeed, when we realize that great swarms of still another species, sEschna eremita, have been seen in annual, September flights at She- boygan, which is on our third great route along the shore of Lake Michigan ; and that the only other autumnal migration reported in de- tail in this country, that of Epueschna heros, took place at Fairbury, Illinois, which is the direct continuation of the same route, one dis- covers a remarkably interesting coincidence. It is true that other flight-ways may be defined, and also that a more or less individual wandering course may be followed down country by both insects; but it seems equally true that the great water-barriers of the ocean and the Lakes divert both migrants into the common and crowded paths already described.

Such a fundamental coincidence prepares one for further identities between these routes and the flight-lines of migratory birds. This ig, indeed, the remarkably interesting fact. For not only does a great flight-way extend along the eastern coast and along Point Pelee, indi- cating a coincidence there, but studies at Toronto, by Fleming, suggest that a great east-and-west flight- way for birds may pass through that city, a possible parallel to our second insect ronie along the northern shores of Lake Erie and Lake Ontario.

Regarding the third route along the Michigan shore, as well as the fourth route through the West Central States, it may be said (and this statement also applies to the eastern flight-ways), that the stronger fly- ing birds are not so easily diverted as the insects: theit southward flight follows a broader, bolder course. So, although birds doubtless follow a migratory course in most, if not all, of the regions defined above, the presence of feathered travelers on the southern shores of Ontario, and thence down the Genesee Valley, as well as other records farther west, show that the higher flying birds are more independent of land-contours than the feebler insect. And, although the bird is locally diverted by food supplies, the greater numbers of the migrants seem less slavishly diverted by geographical features than the insects which, in many cases, assume a lower habit of flight.

Yet, whatever effect further data may have upon the theory of a general similarity of route, there is, in certain local cases, an actual identity or veritable coalescence of the vast stream of mingled life that deviously finds its flooding way to the South. For where certain phys- ical features combine to form narrow contracted flight-ways many types of both creatures are often thrown into a common path which

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