Life Underground: Burrowing Owls & Soil Texture
Scientific Poster Abstract: WSU Academic Showcase (25 March 2011)
We studied burrowing owls, soil texture, and temperature environments of artificial and natural burrows on the Hanford Site and concluded that air temperatures in burrows were unlikely to explain burrowing owl distributions, however, limited density of deep burrows and other site and landscape-level factors may be important.
The burrowing owl (Athene cunicularia) is endangered in Canada, threatened in Mexico, and is a species of conservation concern in the United States because of a contracting breeding range and apparent decline in some regional populations. We studied both natural and artificially constructed burrows at the Hanford Site in the desert of southeastern Washington to explore whether basic environmental characteristics of burrows (e.g., soil texture, burrow length, ambient internal temperature, availability on landscapes) were potentially related to use by nesting burrowing owls.
Soil texture is generally believed to affect burrowing owl distributions by influencing distributions of key mammals (e.g., badgers) that dig the burrows used by nesting owls. We located 129 mammal burrows on 61 transects in 3 soil types and developed regression tree models illustrating that while burrow density was higher in silt loam soils, these soils contained lower densities of nesting owls than sandier soils. However, the availability of deeper burrows may be a limiting factor as < 9% of the burrows were considered deep enough (> 1m) to be used by nesting owls. Ambient air temperature differed among soil types in artificially constructed burrows but not among previously used real nest burrows, suggesting that orientation, length, and convolution of burrows may influence convective heat exchange and confound comparisons of burrow environments. We conclude that soil-related differences in burrow density and burrow temperatures are not likely to explain burrowing owl distributions, but other site and landscape-level factors may be important.
K.B. Larson, Pacific Northwest National Laboratory, Richland, WA
R.D. Sayler, Washington State University, Pullman, WA