Surveys are flown over the same route (transect) each week. These counts estimate the number of birds seen on the routes only, not the entire refuge. Survey numbers are used to describe general trends in the number of waterfowl resting and feeding on the Refuge through the years. Survey results are also used by managers, hunters and birdwatchers to monitor the progress of migration. Biologists use the number as a tool to assess waterfowl use (often referred to as carrying capacity) in response to management actions. Duck, goose and tundra swan use is influenced by off-Refuge factors such as continental populations and habitat and weather conditions throughout the Flyway. On the Refuge, food availability and the extent of human disturbance, such as hunting and boating, greatly influence the number of birds present.