All the geese traveling south along the Pacific flyway to the Central Valley belong to the same family of birds, Anatidae, and one would think Mother Nature would have some sort of family plan for Her migrating, feathered creations which allows them to fly together in one massive flock. But, the whole kit and caboodle of them don’t show up here at the same time and there are reasons for that.
Four species of geese spend winters locally, the Greater White-fronted goose (Anser albifrons), Snow goose (Anser caerulescens), Ross’s goose (Anser rossii) and Aleutian cackling goose (Branta hutchinsii leucopareia).
Greater white-fronted geese, which don’t really have a white front other than an area on their face around their pink-orange bill, are the first to arrive starting in September just as refuges and duck clubs are beginning to “flood up.” The white-fronts take advantage of upland grasslands, fallow agricultural fields, and unflooded rice fields for foraging, so they arrive before wetlands and rice fields have flooded widely across the valley. The Aleutian cackling geese have much the same diet and are next to arrive beginning in mid-October. On local national wildlife refuges, the Aleutian geese favor corn fields grown on the refuges specifically for their use.
Ross’s geese are next to arrive from their breeding grounds in the far north coastal areas of the arctic, usually in mid-November. The birds graze on short grasses in open fields like their bigger cousins but spend their nights roosting in wetlands. Therefore, they like to arrive after flooding is well underway. Ross’s geese are nearly identical in appearance to their cousins, the snow geese, but are significantly smaller – only half the size of snow geese by weight. Smaller organisms have a much greater surface-area-to-mass ratio than larger organisms. The significance is that smaller animals lose their body heat much more readily and have to expend more energy to keep warm. Therefore, when temperatures in the arctic begin to drop, the smaller geese need to head south to warmer conditions.
Larger Snow geese can handle slightly colder temperatures, so they in the north a little longer than their smaller cousins, arriving in the San Joaquin valley a little later. They also like to dig for tubers in wetlands, so they prefer to arrive after there is plenty of standing water.
All four of these goose species can be seen on the local national wildlife refuges through the winter until approximately the end of March. Together, they comprise a wintering population exceeding 100,000 geese. The Ross’ and Snow geese, collectively referred to as “white geese,” alone number nearly 60,000 by the time they’ve all arrived in mid-to-late December. The white geese provide an incredible spectacle at the Merced NWR on Sandy Mush Road (south of Merced) that is worth the drive.
The individual goose species tend to depart in the same order as they arrived, so visitors to the refuges may still be able to see greater white-fronted geese into early April, since they’re the last to depart. When visiting the San Luis NWR, look for geese in the upland grasslands, as well as the wetlands while driving along the Waterfowl Auto Tour route.
