GEOGRAPHIC-VARIATION IN MIGRATORY BEHAVIOR OF GREATER WHITE-FRONTED GEESE (ANSER ALBIFRONS)

We studied the migration and winter distribution of adult Greater Whit e-fronted Geese (Anser albifrons frontalis) radio-marked on the Yukon- Kuskokwim Delta (YKD) and Bristol Bay Lowlands (BBL) of Alaska from 19 87 to 1992. The major autumn staging site for geese from both breeding areas was the Klamath Basin on the California/Oregon border. However, temporal use of this area differed markedly between populations. Gees e from the BBL arrived at the Klamath Basin nearly 30 days before gees e from the YKD and departed before most YKD geese had arrived. Ninety percent of BBL geese used the Klamath Basin in autumn, whereas 30% of YKD geese bypassed the Klamath Basin during autumn and instead new dir ectly to the Central Valley of California. Nearly all BBL geese migrat ed directly from the Klamath Basin to wintering areas in Mexico, bypas sing the Central Valley. Ninety percent of the BBL geese wintered in M exico, as opposed to <20% of the YKD geese. Wetlands of the Interior H ighlands in the state of Chihuahua, particularly Laguna Babicora, were used by >90% of the radio-marked geese in Mexico. Marshes along the W est Coast comprised the other important wintering habitat in Mexico. T he Sacramento Valley of California was the predominant wintering area for YKD geese. BBL geese migrated north from Mexico into the San Joaqu in Valley or Sacramento-San Joaquin Delta of California by the last we ek of January. Fifty-Eve percent of the BBL population used the Klamat h Basin in spring, but many birds staged in eastern Oregon and western Idaho. In contrast, geese from the YKD staged almost exclusively in t he Klamath Basin during spring before flying to staging areas in Alask a. Breeding allopatry and temporal partitioning on staging and winteri ng areas likely has contributed to the evolution of previously describ ed phenotypic differences between these populations. These two populat ions, along with the Tule Greater White-fronted Goose (A. a. gambeli), may constitute a portion of a Rassenkreis, a group of subspecies conn ected by dines, each ecotype of which has independent conservation nee ds.