54. CIRCULAR 363, U.S. DEPARTMENT OF AGRICULTURE 
of damp meadows, it was originally cut off from the Western States 
by the intervening ‘arid regions. But with the advent of irrigation and 
the bringing of large areas under cultivation, small colonies of nesting 
bobolinks have appeared at various western points, and now the 
species is established as a regular breeder in the great mountain parks 
and irrigated valleys of Colorado and elsewhere almost to the Pacific 
coast. In retracing their course to reach the western edge of the 
route followed by the bulk of the bobolinks that breed in the northern 
United States and southern Canada, these western pioneers must fly 
long distances along a line that runs almost due east and west. 
Similarly it is possible to sketch what seems to be the logical 
evolution of the remarkable routes of the golden plover (fig. 22). 
It may be assumed that the eastern birds of this species first followed 
an all-land route from the South American winter quarters through 
Central America, Mexico, and Texas to the western parts of the 
Mississippi Valley. As the migration route lengthened northward 
with the retreat of the ice and the bird’s powers of flight developed, 
it would have a tendency to straighten the line and to shorten it by 
cutting off some of the great curve through Mexico and Texas. 
First a short flight across the western part of the Gulf of Mexico was 
probably essayed. Proving successful, this was followed by flight 
lines that moved farther east, until finally the roundabout curve 
through Texas was entirely discarded and the flight made directly 
across the Gulf to southern Louisiana. 
As the great areas in Canada were gradually added to the bird’s 
domain, other important factors arose, the chief being the attractive- 
ness of the vast stretches of coast and plain of the Labrador Peninsula, 
which in fall offered a bountiful store of berries. The fall route there- 
fore worked eastward to the Gulf of St. Lawrence thence southwest 
through the interior to the coast of Florida and across the Gulf of 
Mexico to the Central American mainland. A series of shortening 
flights followed to take out the great curve of the New England coast. 
A relatively short ocean flight was probably attempted, say from 
Cape Cod to the Bahama “Islands, Cuba, and Jamaica, followed 
eventually by the long direct oceanic route as it is now known. 
As the Labrador Peninsula in spring is bound by frost and shrouded 
by fog while the season advances rapidly through the interior, the 
oceanic route proved useful only in fall, and the spring flight continued 
through the Mississippi Valley. The ‘above outline gives a probable 
and fairly plausible explanation of the origin of this wonderful route, 
particularly when it is remembered that migration routes as now 
known are evolutions—age-long modifications of other routes. 
The evolution of the migration of the Pacific golden plover may be 
explained in a similar fashion. At first the route probably followed 
the Asiatic coast, through the Malay Peninsula and Oceania, thence 
east In a great curve to the Low Archipelago, with individuals and 
flocks dropping out to winter at many points along the way. The 
Siberian birds probably continue to follow this ancient flyway, but 
those nesting in Alaska began a long evolutionary series of flights 
that cut down the length of their journey by shortening the curve, 
until finally the transoceanic route of the present day was developed. 
