UC Davis

Competition is one of the most important biotic interactions influencing animal communities and species distributions. In the Central Valley of California, several species of waterfowl compete for space and food during winter. Goose populations are increasing in California and the Pacific Flyway and are now at levels well above population targets. The growing numbers of geese may have negative impacts on smaller-bodied members of the Anatidae family. To evaluate the potential of this growing conflict, we used high frequency GPS-GSM telemetry to track 211 individuals of four species of geese: the Lesser Snow goose (Anser caerulescens caerulescens), Ross’s goose (Anser rossii), Pacific White-fronted goose (Anser albifrons sponsa), and Tule White-fronted Goose (Anser albifrons elgasi; hereafter referred to as Tule goose) across the Sacramento Valley (the northern portion of the Central Valley) of California. Using step selection analyses, we modeled how field type, photo period (day or night), habitat condition (wet or dry) and age of those habitat conditions impact goose use and habitat selection. All species showed a strong preference for wet rice habitat at night, but daytime preferences varied. Lesser Snow and Pacific White-fronted geese were most similar, selecting wet fallow and dry rice habitats over wet rice and dry fallow during the day. Conversely, California species of concern, Tule geese, strongly preferred wetlands while Ross’s geese preferred dry rice, followed by wet and dry fallow habitats. Habitat age was important and the preference for wet rice and wetlands decreased over time, while selection of dry rice and wet fallow generally increased with age. Due to agricultural flood regimes, wet rice habitats likely offer substantial quantities of nutrient dense food resources to arriving migratory birds. However, over time, heavy consumption and decomposition caused by water cover reduces the attractiveness of this habitat, coinciding with the period which birds often switch to green browsing in other habitats.