Laserfiche WebLink
<br />e. <br /> <br />easily accounted for in these recommendations, but we believe that these <br />recommendations will minimize the probable harm to any individual <br />mouse, preserving the potential contribution, however, small. <br />By necessity, the Science Team is presenting numbers that are more <br />precise than are practically applied by ditch maintenance practitioners. In <br />addition, the measurements are often taken by researchers in the metric <br />system. I have rounded of the numbers to the nearest foot where <br />applicable while providing English equivalents. However, the concepts <br />applied here have, in many cases, only moderate levels of confidence <br />because of the conceptual nature of the discussion. Therefore, the <br />rounding of numbers or slight adjustments that may be desirable for ease <br />of application are defensible. <br /> <br />. <br /> <br />II. ISSUE 1 <br /> <br />Minimum patch size for an isolated habitat patch, <br /> <br />. <br /> <br />Patches of shrubs occur along ditches at varying distances from similar nearby patches. <br />Under what conditions are these isolated vegetation patches likely to be occupied by <br />PMlM? PMlM can travel up to one mile along stream corridors and has been captured in <br />small riparian shrub patches. What is the minimum shrub vegetation patch size that <br />is likely to be occupied by PMJM and how far from suitable habitat can this patch <br />occur? <br /> <br />Diagnosis <br /> <br />Theory: There is little applicable theory available. However, for an animal to be <br />.able to survive long enough to reproduce necessitates there being adequate <br />resources available to support the individual. We concluded that a minimum <br />home range size is a likeiy estimator of the smallest area that will support a <br />PMJM individual at the specific location where the home ranges were <br />calculated. <br /> <br />. <br /> <br />Data: There are few data available to analyze these questions. However, some <br />observations and earlier studies shed some light on the natural history involved. <br />PMlM is not territorial (Whitaker 1972), but often returns to the same place <br />repeatedly to sleep, nest, etc. (T. Shenk, 1999, unpublished data). Home range <br />sizes were calculated for 5 mice along Monument Creek in the U. S. Air Force <br />Academy. The home ranges were .25 - 4.2 acres (0.1 - 1.7 ha) with a mean of 3 <br />acres (1.2 ha) (R. Schorr, 1998, unpublished data). The Science Team concluded <br />that a minimum home range size was a suitable estimator for minimum <br />patch size [the minimum area in which a PMJM individual could dwell and <br />survive long enough to reproduce successfully. Smaller areas are assumed to <br />be insufficient for occupation]. <br /> <br />3 <br />