The habitat of nesting whooping cranes

Abstract

Through a spatial, multi-scale approach I compared available habitat with habitat used by whooping cranes ( Grus americana) on their nesting grounds in Wood Buffalo National Park, Canada. Thirty-two study sites (16 used, 16 available) were established in the nesting area in August 1996. Data were gathered by (a) plots of 9.8 m radius which provided detailed site data and served as ground truth for (b) concentric circular plots of 25, 50, 100, 200, and 500 m radius in which 21 cover types were mapped onto false color infrared 1:15,840 airphotos. Whooping cranes chose habitat that differed from a random sample. Habitat selection was strongest at the nest site, where many attributes of habitat type and structure were evident. Beyond 200 m radius from the nest site, selection was evident solely as avoidance of unsuitable habitat. At the nest site scale (9.8 m radius), the preferred habitat was visually open, with large amounts of open water (median depth 7 cm in August), nearby which there were a few abundant vegetation species in an open spatial arrangement. Habitat types used by whooping cranes were diatom ponds, bulrush ( Scirpus validus) marshes, bulrush/cattail ( Typha latifolia) mixed marshes with aquatic macrophytes, and shrubby mixed marshes with water sedge ( Carex aquatilis) and cattail. Plant species diversity of the entire crane area is low, particularly that of nesting sites. In contrast, spatial diversity of community types is a marked characteristic of the area; average patch size is <1 ha. At the 78.5 ha scale (500 m radius), there were no apparent differences in landscape structure or diversity between used vs available habitats. MANOVA/repeated measures and multi-response permutation procedures were used to examine habitat selection at five spatial scales. Whooping cranes selected bulrush marsh out to a radius of 200 m from the nest, and avoided featureless shrub bogs and fens out to a radius of at least 500 m from nests. Historical and present nesting habitat share the following characteristics: small shallow lakes and ponds, willow communities, marshes of bulrush and cattail, mudflats, and perhaps sedge meadows. The present nesting habitat may be atypical compared to the core of the historical range in its diatom ponds, gypsum karst-groundwater discharge hydrogeology, and permafrost. Cranes appear to use only a small portion of the total available area of their nesting grounds. The Wood Buffalo–Aransas whooping crane population should not be limited by available breeding habitat in the near future.