Occurrence and density of breeding passerine birds in shrubland habitats in Utah
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The Utah Avian Conservation Strategy (Parrish et al. 2002) published by the Utah Partners in Flight (UPIF) Program ranked a total of 24 habitat types and 231 bird species with respect to their need for conservation action. The 24 habitat categories were grouped within five major categories, Riparian, Shrublands, Grassland, Forest, and a collection of additional categories unique to conservation planning efforts in Utah. Shrublands comprise the most abundant of these habitat categories, with sagebrush communities (2.9 million ha) second only to greasewood/halogeton dominant shrublands (5.5 million ha) in total abundance statewide. Various terminologies have been suggested for referring to western shrublands. The term ‘shrubsteppe’ technically refers to shrublands that include a substantial portion of native grass (e.g., ‘steppe’). However, the term shrubsteppe or ‘sagebrush steppe’ has more recently been used to refer to sagebrush (Artemesia sp.) shrublands only (Paige and Ritter 1999). In addition, some bird species have been referred to as ‘obligates’ in sagebrush habitats, including Sage Grouse (Centrocercus urophasianus), Sage Thrasher (Oreoscoptes montanus), Sage Sparrow (Amphispiza belli), and Brewer’s Sparrow (Spizella breweri) (Braun et al. 1976). Terms such as ‘shrub obligates’, or ‘sage obligates’, or ‘shrubsteppe obligates’ have been applied to these species with the assumption that they are “almost entirely dependent” on sagebrush for their existence (Braun et al. 1976, Knick and Rotenberry 1995, Saab and Rich 1997). On the other hand, Braun et al. (1976) suggested that birds are more adapted to the structure of a shrub community rather than to the particular species of shrub that is present.