Tracking the Preble’s Mouse

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by Larry MacDonnell, Sustainability Initiatives, Boulder


Turning east and crossing over I-25 south of Monument, we parked our car on the side of the road and walked down the hill to a marshy meadow watered by Dirty Woman Creek. It was 6:00 a.m. on a Sunday morning. We were on our way to check traps set the night before. Our target was the Preble’s meadow jumping mouse, listed in May 1998 as “threatened with extinction” under the Federal Endangered Species Act.

Mark Bakeman, a biologist with Ensight Technical Services, shooed away a small herd of horses grazing near his traps. Working for the Colorado Department of Transportation, Mark is one of a small group of scientists who have been studying the mouse in recent years. Trapping is used to determine the presence of mice in their only known habitat in the world — along the Front Range of the Rockies in Colorado and southern Wyoming.

Mark has trapped sections of this reach of Dirty Woman Creek from just east of I-25 to its confluence with Monument Creek in other seasons. He is interested in changes in the number of mice trapped during his seven-day field session and the influence of barriers on mouse movement patterns. With the help of his assistant, Norm Clippinger, he inserts a small pit tag into the skin of trapped mice. This enables him to identify mice that have already been trapped and to determine how much mice move around on a daily basis. He weighs and measures each mouse and notes its sex. When he releases a mouse, it disappears with amazing speed.

On this particular morning, we find 11 of the elusive mice in the 400 traps scattered through the riparian area on both sides of Dirty Woman Creek in this roughly 1.5 mile segment. True to form, we find the mice in traps set within a few feet of the creek. We find them in areas with good vegetative cover — willows and tall sedges. We find them within 100 feet of I-25 (in a later field session, Marks traps a mouse within six feet of I-25) and within 300 feet of a housing development. It’s clearly not wilderness they need, but water and plant cover.

The results of Mark’s research feed into the work of a recently constituted Preble’s meadow jumping mouse science team. Led by Chris Pague of The Nature Conservancy, the team is to identify and evaluate threats to the mouse’s viability. This team, of which Mark is a member, presented its draft analysis to the Boulder County subarea group on September 1. It was the group’s third meeting since the State of Colorado initiated a formal collaborative planning process in January 1998. Greatest threats identified in Boulder County are habitat conversion caused by residential and commercial development, predation by cats, hydrological changes, and disease. Threats characterized as of medium importance included habitat fragmentation, catastrophic fire, hay farming, high impact grazing, and trail development and use. Similar threat analysis has taken place for the other Colorado counties within the range of the mouse. The next step is to identify strategies for successfully managing these threats.

The U.S. Fish and Wildlife Service has not yet issued its “4(d)” regulation governing conservation of the threatened Preble’s mouse. This regulation will set out protective conditions applying to activities that might further harm the species. Meanwhile, the state’s planning process proceeds in its effort to develop habitat conservation plans involving commitments by counties, cities, and others to assure protection of mouse habitat.