Conservation Status of Ochlodes Yuma Anasazi Cary and Stanford

Conservation Assessment of Ochlodes yuma anasazi (S. Cary and Stanford) Final Report to New Mexico Department of Game and Fish pursuant to contract no. 11 516 0000 00025 Steven J. Cary, Linda S. DeLay and John J. Pfeil Natural Resource Institute Santa Fe, New Mexico December 29, 2011 TABLE OF CONTENTS page Introduction . 3 Previous Work . 4 Study Area . 5 Methods . 8 Results . 10 Life History and Ecosystem Services . 10 Distribution of Host Reed. 12 Breeding Distribution of OYA . 12 Population Structure of OYA . 15 Dispersal of OYA . 15 Vulnerability . 21 Threats . 21 Future Work . 25 Literature Cited . 27 Appendix A: Location of Reed Patches . 31 Appendix B: Adult OYA Observations . 36 Appendix C: Detailed Reed Patch Maps . 39 Acknowledgements The authors gratefully acknowledge the assistance of volunteers who made our jobs much easier. Randy Merker, Chuck Noble and Paige Prescott assisted with our float through the La Junta reach of the Rio Grande. Paige's sharp eye quickly spotted larval shelters in reed patches. Jane Pfeil provided excellent note-taking and admirable culinary support. Doug Bland and Eric Rounds provided welcome driving, navigation and photography support. Bureau of Land Management biologist Valerie Williams gave helpful comments on a working draft of this report. Cover: Male Ochlodes yuma anasazi perching for females on Phragmites australis leaf at Little Arsenic Springs, August 26, 2011, by S. Cary. 2 Introduction Yuma skipper, Ochlodes yuma (W. H. Edwards 1873), is a 2.5cm-long butterfly (Figure 1) whose occurrence spans much of the American West and Southwest (Figure 2). Across this broad geographic range its habitats are defined by the presence of one plant species: common reed [= Phragmites australis (Cav.) Trin. ex Steud.]. In the semi-arid southwestern U. S. this obligate wetland plant is restricted to marshes, watercourses, pond edges, seeps, sloughs, springs and irrigation canals. Despite occurring in many western states, most populations are present only in narrow ribbons or pockets of habitat often separated from other populations by many miles of reed-less terrain (Scott et al. 1977). Colonies of O. yuma often seemed hosted by reed patches that seem quite small, sometimes only about 300 m2, and in one case only 5 m2 (Scott et al. 1977). Only rarely were adults found more than a few meters from stands of the host plant (Scott et al. 1977). Conservation organizations weighed O. yuma occurrence in most U. S. states west of the Rocky Mountains, concluded it is globally secure, and assigned it a Heritage Global Rank of G5 (www.natureserve.org/explorer). Figure 1. Ventral view of Ochlodes yuma anasazi. Photo Aug. 14, 2009, by S. Cary. At the perimeter of the overall range of O. yuma are several small satellite populations that appear to be geographically and reproductively disjunct from the general population center of the species in the Intermountain West. Outlier populations exist in Oregon, Washington, Wyoming and New Mexico (Figure 2). Those in Oregon and Washington were tentatively placed with Nevada subspecies O. y. lutea. Washington populations were assigned a state conservation rank of S1 (critically imperiled) (www.xerces.org/yuma-skipper/). Another outlier, O. y. anasazi (OYA), is restricted to northern New Mexico and the Rio Grande watershed. It was described as a distinct subspecies (Cary and Stanford 1995) and Pelham (2008) tacitly affirmed its phenotypic differentiation and genetic isolation from other O. yuma colonies. Due to lack of detailed published information about this subspecies, its conservation status has yet to be established (e.g., www.xerces.org/yuma-skipper/). The Share with Wildlife program of the New Mexico Department of Game and Fish funded this study to analyze its biology, habitat, distribution and threats and develop a conservation assessment. 3 Figure 2. County distribution of Ochlodes yuma (www.butterfliesandmoths.org/). Previous Work Wheeler Expedition naturalist Ferdinand Bischoff made the first collection of Ochlodes yuma in 1871 in southern California (Brown 1957, Brown and Miller 1980). W. H. Edwards (1873) used those specimens to formally describe the species two years later. Skinner (1899) described Pamphila scudderi from western Colorado, but this taxon was later synonymized with O. yuma (Miller and Brown 1981). Information about O. yuma accumulated slowly (e.g., Tilden 1957). Its affinity to marshy habitats was recognized early (e.g., Brown et al. 1957), but its larval host plant remained unknown until 1974 when a female was observed placing an egg on a basal leaf of Phragmites australis (Scott et al. 1977, Scott 1992). The distribution of O. yuma was long thought to include only Arizona, California, Colorado, Nevada and Utah (e.g., Garth 1950, Ferris and Brown 1980). Some 20th Century Colorado workers (Scott et al. 1977) found “no geographic variation” across this broad western reach of O. yuma. Ferris and Brown (1980), however, were skeptical of this putative uniformity because modern populations seemed to have been “isolated from one another for thousands of years.” Understanding of the distribution of O. yuma has improved since 1980. Peripheral colonies were discovered in the states of Wyoming and Idaho (e.g., Stephens 2002), Oregon and Washington (Pyle 2002), and New Mexico (Cary and Stanford 1995). These discoveries demonstrated that O. yuma occurred beyond the boundaries of the Colorado River basin and the Intermountain West. Discernment of morphological differences within its far-flung range finally allowed Pelham (2008) to recognize the following distinct races of O. yuma: the nominate race of O. y. yuma in southern California; O. y. scudderi in western Colorado; O. y. lutea in north-central Nevada and the Pacific Northwest (Austin 1998); O. y. sacramentorum in California’s Central Valley (Austin 1998); and O. y. anasazi in northern New Mexico (Cary and Stanford 1995). Nothing has been published about OYA since its original description. More than 30 years of detailed butterfly observations around New Mexico by the senior author produced no other O. yuma sightings. One anecdotal, unconfirmed report of O. yuma from near Shiprock in San Juan County, NM, is most likely western Colorado subspecies O. y. scudderi. 4 Study Area All known occurrences of OYA are associated with the Rio Grande Gorge, a major physiographic feature extending the length of Taos County in northern New Mexico (Figure 3). Figure 3. Map of the Rio Grande Gorge study area in Taos County, NM. 5 Along that distance of more than 100km the Rio Grande has excavated a steep-walled canyon through thickly layered basalts and related sediments (Figure 4). The Gorge begins as a small notch near the Colorado state line, deepens to a defile more than 250m deep, then broadens into a flat-bottomed canyon north of Española. Over this distance the Rio Grande falls from 2267m above sea level at the Colorado border to 1790m above sea level at the Rio Arriba County line. Figure 4. Rio Grande Gorge looking north from trail toward Big Arsenic Springs. S. Cary photo Aug. 26, 2011. The Rio Grande Gorge is deeply incised into the Taos Plateau which, at 2287m elevation, occupies the valley between the Sangre de Cristo Mountains on the east and the Tusas Mountains on the west. Geologically this "low" spot is the southern portion of the San Luis Basin, which is the northernmost structural basin of the continent-scale Rio Grande Rift, which continues south into Texas and Mexico. The Taos Plateau represents the top of a 200 km3 layer-cake of basalts termed the Servilleta Formation. These basalts began as lava erupted from shield volcanoes that are still evident only a few kilometers to the west. As described by Bauer et al. (2007), these lavas flowed “as thin, molten sheets for tens of miles before solidifying.” Episodic eruptions between 4.8 and 2.8 million years ago built up more than 200m of basalt in this part of the San Luis Basin. Servilleta basalts are highly permeable as a result of extensive fractures and columnar joints that are open and vertically continuous, combined with deposits of sand and 6 gravel deposited between individual basalt flows (Bauer et al. 2007). Several Rift-related fault systems intersect the Gorge and are significant conduits for water movement (Bauer et al. 2007). By New Mexico standards, Taos County is rich in surface waters because it hosts the state’s highest upland, the Sangre de Cristo Mountains, a linear range which parallels the Gorge several miles to the east. These uplands generate orographic precipitation exceeding 50 cm/yr (e.g., www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?nm7323), which in turn supports numerous perennial streams and rivers. Three of these are important tributaries to the Rio Grande in the study area: Red River, Rio Hondo and Rio Pueblo de Taos. As these and lesser watercourses exit the uplands and head west and southwest toward the Gorge, water infiltrates downward through the coarse sands and gravels of alluvial fans and foot slopes and into the highly fractured basalts below. Infiltrating waters recharge local groundwater, some of which discharges to the Rio Grande through more than 150 springs in the channel bottom, along channel banks, and from canyon walls as much as 120m above the river (Bauer 2011). Many of these springs are clustered where the Gorge cuts across major geologic faults (Bauer et al. 2007). Plant communities in the study area exhibit characteristics of an inverted ecosystem: mesic pine woodlands occur at lower elevations than semi-arid shrub-steppe, when the normal relationship is reversed. Vegetation on the Taos Plateau is semi-arid grassland and shrubland dominated by big sagebrush (Artemisia tridentata) mixed with soapweed yucca (Yucca glauca) and grasses including blue grama (Bouteloua gracilis). Among woody plants, piñon pine (Pinus edulis) and one-seeded juniper (Juniperus monosperma) are locally favored.

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