Parkwide Aerial Surveys

Currently the bulk of beaver research and censusing in Yellowstone depends upon park-wide aerial surveys that are conducted every other fall. Researchers have standardized fall counts because beaver families are more easily identified as separate groups within distinct territories in the fall when they have selected their wintering spots and begun their food caches and lodge building. Using the standard, efficient technique used by other beaver researchers, park biologists follow a prescribed flight path from a small fixed-wing aircraft (Supercub) flying at an altitude of 500 feet. All of the park’s watercourses, ponds and lakes of suitable gradient for beavers to dam are surveyed once; high-density areas may receive multiple over-flights to accurately locate every colony. Using food caches as the unit of measurement, researchers look for several “auxiliary hints” to help identify working colonies. Some of these signs include (1) freshly peeled sticks that shine white on the water and are easy to spot from the air; (2) brimming dams that hold still water; (3) lodges made with fresh mud and green sticks; and (4) actual beavers slapping the water surface. In addition, known preferred beaver habitats are given special scrutiny, as are deep water bends, which possess the ideal hydrology for damming.