Analysis of Spring Migration of Lapland Longspurs to Alaska

West, George; Peyton, Leonard; Irving, Laurence

Lapland Longspurs (Calcarius lapponicus alascensis) migrate in large numbers northwestward from their wintering grounds in western United States and southwestern Canada to Alaska in spring to breed on the treeless arctic and alpine tundra. The migrations follow three general routes as determined by dates of first arrivals of males which make up over 90 percent of the initial component of the migrating population: (1) the coastal route along the Pacific shore of British Columbia and Alaska, some entering the state through mountain passes towards the Yukon River in the eastern part of Alaska, (2) the intermountain route in the mountain trenches of British Columbia and southern Yukon territory and Alaska, also reaching the southeastern portion of the Yukon River drainage, and (3) the prairie route, from the prairies of Alberta and eastern British Columbia west and north to the Yukon drainage and probably also north to the Mackenzie River Delta. The sex ratio changes gradually; initial flocks on each route are composed of 90 percent males, the last flocks seen consist of about 25 percent males. The total time for the population to pass a given point varies from year to year and the rate of sex ratio change varies accordingly. Consequently it is possible to determine the stage of migration by examining the sex ratio of flocks at any given place and time. From the gradual disappearance of color marked birds and the changing sex ratio in apparently stably located flocks of constant size, it is proposed that individual longspurs pursue their own program of migration. Each is impelled by his own changing physiological state in the time sequence of migration. They arrive, feed, and leave an area as they are ready, probably joining in migratory flocks composed of individuals in synchronous condition. Longspurs deposit fat en route; in one example the rate of deposition was 0.76 g of fat per day for 4 days. The analysis of the migration of lonspurs to Alaska has provi

Analysis of Spring Migration of Lapland Longspurs to Alaska

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