Nest habitat selection of burrowing owls in relation to soils, burrow availability, and burrow temperature

Kyle Blake Larson

The availability of mammal burrows is often considered the most important habitat requirement for burrowing owls (Athene cunicularia), but little is known regarding factors that affect the density and distribution of fossorial mammals and their burrows, and how they ultimately influence habitat selection of burrowing owls. Soils are believed to play an important role in this relationship, particularly with respect to habitat selection at a landscape scale. In this study, I assessed whether burrowing owls in southcentral Washington prefer to nest in certain soils, and whether selection corresponds to increased burrow availability in those soils. I also evaluated whether the association between burrow temperature and soil texture may be one factor influencing nest habitat selection of burrowing owls. Roadside surveys conducted in 2007 and 2008 indicated that the density of burrowing owl nests in the study area was quite low (0.14 nests km-2). Comparisons between use and predicted burrowing owl habitat did not show an association between habitat selection and soils, although burrowing owls did nest more frequently in loamy sand and sandy loam soils. Soils influenced the distribution and abundance of badger (Taxidae taxus) burrows, which are the primary type of burrow used by burrowing owls in eastern Washington. However, habitat use by nesting burrowing owls was not correlated with the availability of badger burrows in the primary soils. Owls nested in soils where burrows were both abundant and rare. Field tests comparing temperature inside simulated nest burrows indicated that burrow temperature was significantly different among soil textures, and that burrow temperature was inversely related to the amount of coarse material (sand) in the soil. However, I failed to detect a relationship between soil texture and temperature inside burrows that had been previously occupied by burrowing owls, although sample sizes were low for this comparison. Hence, differences in burrow temperature related to soil texture alone are not likely to explain why burrowing owls may associate with certain soils. Temperature differences among previously occupied burrows may have been related to burrow characteristics that influenced convective heat exchange (e.g., entrance orientation, tunnel length, convolution), although further research is needed to test this hypothesis.

Nest habitat selection of burrowing owls in relation to soils, burrow availability, and burrow temperature

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