Use of Habitat during Drought by the Common Muskrat (ondatra Zibethicus) in Southwestern Oklahoma

Status of the common muskrat (Ondatra zibethicus) in the southern High Plains and western Rolling Plains has remained uncertain due to a scarcity of records. I examined diversity of riparian habitats, frequency of occurrence of habitats, availability of habitats, and use of habitats by muskrats within an irrigation drainage system in southwestern Oklahoma during prolonged drought. Six major habitats were supported in 31 km of drainage channels. These included, in order of descending frequency, emergent cattails, prairie sedge meadow, cattail-forested transition, forest, turf grass, and pioneer mudflat. Of habitats in drainage systems, 60% were available for muskrats as defined by presence of water. Availability differed among habitats; prairie sedge meadow had highest availability and emergent cattails was the lowest in availability. Use of habitats differed significantly among habitats and was driven by availability. RESUMEN—El estatus de las ratas almizcleras (Ondatra zibethicus) en las altiplanicies meridionales y las planicies ondulantes occidentales se ha mantenido incierto debido a la escasez de registros. Examiné la diversidad de hábitats ribereños, la frecuencia de ocurrencia de hábitats, la disponibilidad de hábitats, y el uso de hábitats por las ratas almizcleras dentro de un sistema de drenaje de irrigación en el suroeste de Oklahoma durante un perı́odo de sequı́a prolongado. Treinta y un kilómetros de canales de drenaje sostenı́an seis tipos principales de hábitat, incluyendo en orden de frecuencia descendiente: anea emergente, juncia de prado, anea en transición a forestación, bosque, césped y marisma pionera. El 60% de los hábitats del sistema de drenaje fue clasificado como disponible para las ratas almizcleras de acuerdo a la presencia de agua. La disponibilidad difirió entre los tipos de hábitats; la juncia de prado tuvo la disponibilidad más alta mientras que la anea emergente tuvo la más baja. El uso de los hábitats por las ratas almizcleras varió significativamente entre los tipos de hábitats, y fue determinado por su disponibilidad. The common muskrat (Ondatra zibethicus) is the most widespread and abundant semi-aquatic fur-bearer in North America. Its extensive geographical range coincides with an abundance of suitable wetland habitats (Wilner et al., 1980; Parker and Maxwell, 1984; Dalquest and Schultz, 1992; Clark and Kroeker, 1993; Virgil and Messier, 1996; Engeman and Whisson, 2003). Arid regions of North America where, rainfall is annually and seasonally variable, watercourses often are ephemeral, and permanent bodies of water are few and isolated, mark the southwestern boundaries of the geographic range of muskrats. Southwestern populations persist in isolated habitats such as desert water holes, manmade reservoirs, and agricultural irrigation systems (Dixon, 1922; Storer, 1937; Errington, 1951). Isolation of habitats is attributed to a lack of wetland corridors across southwestern margins of the range (Bolen et al., 1989). Verified records of muskrats in the High Plains-Rolling Plains interface are few and isolated in Texas (Bailey, 1905; Jones et al., 1988; Stangl et al., 1989; Dalquest and Schultz, 1992; Schmidly, 2004a) and Oklahoma (Caire et al., 1989; Braun and Relevez, 2005; McDonald, 2006a). During the 20th century, muskrats largely have disappeared from tributaries of the Pecos and Canadian rivers in western and habitats in northern Texas, respectively (Schmidly, 2004b; F. B. Stangl, pers. comm.). McDonald (2006b) suggested that gradients of abundance of muskrats from east to west and northeast to southeast, as previously described by Caire et al. (1989), are associated with large-scale spatial variations in environmental factors (e.g., The Southwestern Naturalist swna-55-01-06.3d 29/12/09 17:18:38 35 Cust # PS-53 THE SOUTHWESTERN NATURALIST 55(1):35–41 MARCH 2010