Movement of Imperiled Chiricahua Leopard Frogs during Summer Monsoons

—Habitat fragmentation and subsequent disruption of animal movement are responsible for extinctions in some species, including amphibians. Amphibians that can travel across fragmented landscapes may be at lower risk of extinction. Chiricahua Leopard Frogs are threatened because of fragmentation associated with habitat loss and degradation. We sought to identify cues leading frogs to leave perennial ponds and factors related to movement ability of Chiricahua Leopard Frogs in New Mexico during the summers of 2013 and 2014. Using pitfall traps, we captured frogs leaving ponds and radio-tracked 30 individuals to characterize overland movements. We checked traps and located frogs daily for up to eight weeks. We assessed factors related to the number of frogs leaving ponds using linear models and to distances moved by frogs using linear mixed models. The number of frogs caught was related to rainfall, but not water temperature, and more frogs were found outside ponds at an intermediate level of rainfall. Frogs who left ponds moved an average of 97 m/day, but distances were highly variable among individuals. Sex and size did not explain differences in distances moved, after accounting for individual variation. One individual moved 1,658 m in a day and another 9,888 m over 36 days. These distances are farther than recorded previously for this species. Movement data are essential for developing recovery plans for threatened species, and our findings will inform planning by predicting the ability of populations to cope with the effects of habitat fragmentation and the ability of animals to colonize new habitats. Habitat fragmentation is one of the largest drivers of biodiversity loss on the planet (Soulé, 1991). Species that are more mobile can better cope with the effects of fragmentation and are at less risk of extinction (Ficetola and Bernardi, 2004). Amphibians usually are assumed to have relatively limited movement capabilities, affecting their ability to colonize discrete habitat patches (Blaustein et al., 1994). Many species, however, may be able to disperse over long distances (Smith and Green, 2005), allowing them to reach distant habitat patches and colonize previously extirpated patches on the landscape (Fellers and Kleeman, 2007). Maintaining connectivity among patches also may decrease the risk of species extinction by increasing gene flow (Fagan et al., 2002) to ensure persistence over time (Turchin, 1998). Identifying characteristics of individuals or landscapes important for animal movement may be a way to predict and facilitate recolonization of habitat patches and increase persistence of imperiled species. Conserving ‘‘ecological connectivity,’’ or the ability of populations to exchange genetic material and colonize nearby areas, is a main focus for any effective amphibian management plan (Semlitsch, 2000) and requires understanding the movement capabilities of the species of interest (Seburn et al., 1997). Because amphibians need an array of terrestrial and aquatic habitat features, much of the research on spatial ecology of amphibians has centered on quantifying movement between seasonally-used sites (Bull and Hayes, 2002; Matthews and Pope, 1999) and through habitat corridors (Pilliod et al., 2002; Baldwin et al., 2006; Fellers and Kleeman, 2007; Tatarian, 2008). In addition to identifying important habitat features, studies also may identify weather conditions conducive to movement (Dole, 1971) or characteristics of the individual animal that influence its propensity for moving, such as sex or size (Pilliod et al., 2002). Chiricahua Leopard Frogs (Lithobates chiricahuensis) are native to Arizona, New Mexico, and northern Mexico (Platz and Mecham, 1979; Stebbins, 1985), although their historical distribution is poorly known (Sredl and Jennings, 2005). In 2002, Chiricahua Leopard Frogs were listed as threatened under the Endangered Species Act because of fragmentation of extant populations, loss of animals from some ranges, and threats from invasive species and disease (U.S. Fish and Wildlife Service, 2002). Suggested conservation strategies for the species have included removing predators, restoring breeding habitat and corridors, and translocating individuals (Sredl and Howland, 1994). Aside from some basic information about natural history and documentation of population declines, little is known about Chiricahua Leopard Frogs, particularly their movement habits and abilities (U.S. Fish and Wildlife Service, 2002). Some recent studies have focused on spatial dynamics (Chandler et al., 2015; Jarchow et al., 2016) and vital rates (Howell et al., 2016) of populations, but we were interested in how environmental and individual-level factors relate to frog movements. We studied two facets of movement in Chiricahua Leopard Frogs. We aimed to 1) identify the cues associated with frogs leaving water bodies, and 2) assess the ability of frogs to move outside of water bodies to inform management of extant populations and guide translocation efforts in their former range. We hypothesized that rainfall and temperature may influence when frogs leave ponds (Dole, 1971; Kruse and Christman, 2005; Todd and Winne, 2006) and that the relationship between movement and rainfall may depend on the specific characteristics of the landscapes surrounding each pond. We also hypothesized that individual-level characteristics such as sex and size may be related to differences in the distance frogs moved outside of ponds (Fellers and Kleeman, 2007). MATERIALS AND METHODS Study Site. —We conducted research on the Ladder Ranch, a private, 63,300-ha working bison ranch in Sierra County, New Mexico, adjacent to the Gila National Forest (Fig. 1). The Ladder Ranch holds 33% of known populations of Chiricahua Leopard Frogs in New Mexico, and, therefore, is of great importance to conservation efforts for the species (Kruse and Christman, 2005). Elevation in our study area ranged from ~1,700–2,050 m. The Corresponding Author. E-mail: rkhinderer@gmail.com DOI: 10.1670/16-093 ranch is in the Arizona–New Mexico mountains ecoregion and consists of grasslands at lower elevations and Ponderosa pine forests at higher elevations. Riparian vegetation consists mainly of oak (Quercus spp.), cottonwood (Populus spp.), juniper (Juniperus spp.), and willow (Salix spp.). Up to 50% of annual precipitation may fall during July–September in monsoondominated areas of the southwest (Sheppard et al., 2002). For this reason, we conducted our work during monsoon season, when Chiricahua Leopard Frogs are thought to travel overland between water bodies (U.S. Fish and Wildlife Service, 2007). We focused our work within the Seco Creek watershed on the Ladder Ranch. This drainage basin holds a persistent population of Chiricahua Leopard Frogs, especially in earthen livestock tanks along the creek’s length. Within this drainage, we captured frogs at two livestock tanks (North Seco and Johnson Wells) along the creek course with persistent populations of frogs, based on visual encounter surveys conducted over the past decade (MMcC, unpubl. data). North Seco and Johnson Wells (0249044E, 3667208N and 0260489E, 3664241N, respectively, Zone 13S, datum WGS84) are small (~20 m diameter), excavated livestock watering tanks (‘‘ponds’’) filled with groundwater by solar pumps (Fig. 1). Both are vegetated with aquatic plants (especially Typha, Potamageton, and Scirpus spp.) and contained breeding Chiricahua Leopard Frogs during the summers of 2013 and 2014. Johnson Well is ~12 km downstream from North Seco Well. Three other ponds lie between our study ponds at 2.5–3.5 km intervals, and there are several others upstream and downstream (Fig. 1). During the dry season, little to no standing water remains in this section of Seco Creek save these ponds. During monsoons with sufficient rainfall, Seco Creek may flow and pools may remain in the creek between storms. North Seco Well is 22 m from the Seco Creek channel, and Johnson Well is 205 m from the creek