Use of Barn Owl (Tyto alba) Pellets as a Potential Method to Study a Rare Rodent Population in Northeastern New Mexico

In June 2008, I discovered a single jumping mouse (Zapus) cranium in a Barn Owl (Tyto alba) pellet from below an active nest along Cerrososo Creek, Colfax County, northeastern New Mexico. Although the cranium could not be identified to species, this specimen could potentially represent a previously unknown population of the endangered New Mexico meadow jumping mouse (Z. hudsonius luteus). In 2009 and 2010, I collected pellets at 8 Barn Owl nesting or roosting sites along streams in my study area with the following objectives: (1) determine whether Barn Owl pellets could be used to gain information about the abundance and distribution of this Zapus population, (2) use pellets to acquire additional Zapus specimens to aid in positive identification of the jumping mouse species present, and (3) potentially document a previously unknown population of the endangered New Mexico meadow jumping mouse. Focusing only on pellets produced during the Zapus active (nonhibernation) summer period, I dissected 298 pellets containing 487 individual mammalian prey items from 12 genera but did not locate any additional Zapus remains. Examination of owl pellets appears to be a poor survey tool for Zapus, perhaps due to the jumping mouse's short summer active period, natural low population density, and preference for tall, dense riparian vegetation.