Managing grassland pastures at Humboldt Bay National Wildlife Refuge for Aleutian geese

An increasing population of Aleutian cackling geese (Branta hutchinsii leucopareia) has sparked concerns over goose population and public land management in Northwestern California. Strategies are needed to reduce depredation of private agricultural grassland pastures by geese. A Field experiment was conducted to assess the amount of goose grazing in relation to several habitat treatments at Humboldt Bay National Wildlife Refuge. Pasture plots were either fertilized with slow release fertilizer or mechanically cultivated with berseem clover (Trifolium alexandrinum). During spring 2007 an index of grazing pressure was quantified using goose dropping counts. Vegetation quality and quantity were quantified within treatment areas. Fertilizing pastures increased crude protein content of plants and made them more attractive to geese. Fertilized plots received 42% more grazing pressure compared to control plots. Crude protein of vegetation in fertilized plots was 16% higher compared to control plots. Crude above-ground biomass inside exclosures within fertilized plot was 88% higher than control plots. Fertilized plots also produced nearly twice as much standing crop biomass, indicating the potential to increase goose use days available at the refuge. Estimated cost to fertilize one hectare of land was U. S. $89.24. Goose grazing pressure on clover treatment plots did not differ significantly from the control. However, clover plots were potentially so heavily favored by geese during early growth stages that they were not able to become well established in the pastures. Estimated cost to over-seed one hectare of land with clover was U. S. $38.44. Public land managers can contribute to maximizing carrying capacity of grassland refuge areas by managing vegetation to have optimal levels of biomass and crude protein. With this strategy land managers may be able to re-distribute geese across the landscape and reduce goose depredation on private lands.