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Guest Editorial 
This page was last updated on January 06, 2009 .

A Clue to Burrowing Owl Declines on Grazed Grasslands?
by: Stan Moore 10/3/02

The following paper from American Midland Naturalist is based on research in the tallgrass prairie, which is not burrowing owl habitat. So, it should not be applied directly to burrowing owls. But, the herbivore components of the study both occurred historically and currently in shortgrass and mixed-grass prairies which were home to large numbers of burrowing owls.

This sort of ecological understanding may provide a clue to why burrowing owls thrived in grazing regimes of native bison, but have declined in grazing regimes of domestic livestock. Bear in mind, of course that many other factors definitely relate to burrowing owl declines (persecution of keystone fossorial mammals to benefit cattle operations, outright habitat conversion to other uses, etc.), but this one may be overlooked and understudied in those intact vegetative communities where the principal difference between "now and then" is the replacement of native grazers (American bison) with domestic livestock.

Influence of Grazing by Bison and Cattle on Deer Mice in Burned Tallgrass Prairie Matlack, Rayond S. and Donald W. Kaufman, and Glennis A. Kaufman. American Midland Naturalist 146(2): 361 - 368.

Abstract: We studied the influence of grazing by bison (Bos bison) and by cattle (B. taurus) on deer mice (Peromyscus maniculatus) in tallgrass prairie at the Konza Prairie Biological Station in 1997 and 1998. Small mammals were sampled by one 10-station trapline in each of four bison-grazed enclosures, four cattle-grazed enclosures, and four ungrazed ones. Enclosures were 4.9 ha and the biomass of grazers in each was similar. All sites were burned annually. We sampled small mammals for 4 consecutive nights in spring before fire, in spring after fire, and in autumn. Deer mice were the most abundant species (n=225); 83% of all small mammals captured in all treatments and in each trapping period. Deer mice were significantly more abundant in bison-grazed and cattle-grazed sites than in ungrazed sites in spring before fire (P<0.01 and P<0.05 respectively), but were similar in abundance in grazed and ungrazed sites following fire. Abundance of deer mice was significantly higher in bison-grazed sites than in cattle-grazed and ungrazed sites in autumn (P,0.05 and P<0.01 respectively). Bison and cattle differ in grazing and nongrazing behaviors (e.g. wallowing in bison) that result in differences in vegetation structure. It is likely that differences in deer mouse abundance between bison-grazed and cattle-grazed treatments were due to differences in vegetation structure caused by the two types of grazers.

Some questions that might be investigated in shortgrass prairie might be: If bison impact vegetation structure differently as compared to cattle, how might this affect other prey populations of value to burrowing owls, including insects, reptiles, etc.? If fire was intermittent and not an annual process, how would this affect burrowing owls and their habitat? How would the interaction of bison and prairie dogs impact burrowing owls compared to cattle-grazed habitats with or without prairie dogs?

Stan Moore is a falconer, an active participant in bird banding studies, and on the Advisory Board of Western Watersheds Project, Inc.