Habitat selection by Columbian white-tailed deer (Odocoileus virginianus leucurus) along the lower Columbia River

Jonathon David Heale

Columbian white-tailed deer (Odocoileus virginianus leucurus) have been federally protected by the United States government since 1967. Historically inhabiting river valleys and surrounding foothills throughout western Washington and Oregon, USA, they were extirpated throughout most of their range by the early 1900s, presently existing in two distinct population segments (DPS). Our objective was to characterize habitat selection by female Columbian whitetailed deer throughout the lower Columbia River DPS and identify habitat characteristics influencing selection. From 2013-2018, GPS collars were deployed at 3 sites throughout the range of the lower Columbia River DPS and location data collected for deer translocated to Ridgefield National Wildlife Refuge (n = 16) and non-translocated resident deer at two units of the Julia Butler Hansen Refuge (n = 14). We created generalized linear mixed models to evaluate habitat selection at the population level based on a use-availability design, incorporated random effects into the traditional fixed-effects exponential resource selection function (RSF) design to test hypotheses about selection for edge, cover vs. open habitat, and pasture management regimes. As expected, we found that female Columbian white-tailed deer strongly selected for the edge between cover (i.e., containing woody vegetation for concealment or thermal protection) and open (i.e., containing shorter herbaceous vegetation for food) habitats, annually and seasonally. Contrary to our expectation that cover and open areas would be used equally, however, our annual and seasonal models showed a consistent and significant selection for habitats offering cover, especially scrub-shrub and deciduous forest. In summer when cattle were present in the pastures, deer avoided cattle-grazed pastures more strongly than mechanically-managed pastures and unmanaged open areas. In winter, however, we did not see the expected shift in selection from mechanically-managed pastures to cattle-grazed pastures, which have been shown in some previous studies to provide better diversity of herbaceous vegetation for deer. Using our RSF model, we explored potential ways to increase habitat suitability for Columbian white-tailed deer on the Julia Butler Hansen and Ridgefield refuges by adding cover habitat, increasing availability of edge, and changing pasture management. In addition, we used the model to determine the suitability of future reintroduction sites.

Habitat selection by Columbian white-tailed deer (Odocoileus virginianus leucurus) along the lower Columbia River

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