Herpetofauna of Glacier National Park

Abstract

The current distribution of amphibians and reptiles in Glacier National Park, Montana was documented from museum records and field surveys conducted in 1990 to 1992. Eight species were recorded at 141 sites at elevations from 1000 m to 2300 m. Rana luteiventris was the most common amphibian, occurring parkwide to elevations of 1800 m. Ambystoma macrodacEylum occurred in woodlands and wet meadows west of the Continental Divide at elevations between 1050 and 1500 m. This salamander was uncommon on the east side of the park with most sightings recorded in the lower Waterton Valley; none were found in the upper Missouri River drainage. Buto boreas was widely distributed to elevations up to 2250 m, but was not abundant at most locations. Ascaphus truei was found in small, cold, high gradient streams throughout the Middle Fork drainage, but occurred intermittently in the North Fork and upper Missouri ltiver drainages. A single population of A. truei was located in the South Saskatchewan River drainage. The range of Hyla regilla was restricted. Most sightings were made near the community of West Glacier, Montana, or at breeding ponds along the Middle Fork, Flathead River, a few km upstream. Chrysemys picta occurred mostly in the lower Lake McDonald valley at elevations between 1000 and 1120 m. A few turtles were seen in the North Fork drainage south of Polebridge, Montana. Thamnophis elegans was more abundant than the similarly distributed T. sirtalis. The widespread introduction of sport fish in park waters may have reduced amphibian populations in some drainages, notably in some of the high elevation valleys east of the Continental Divide. This content downloaded from 207.46.13.52 on Sat, 22 Oct 2016 04:48:40 UTC All use subject to http://about.jstor.org/terms 18 NORTHWESTERN NATURALIST 78(1) an, and terrestrial habitats. Intensive area searches were employed instead of more rigorous sampling methods (i.e., time-constrained searches, trapping, etc.) to ensure maximum coverage within the budget constraints and time available for the survey. Searches were conducted along major stream courses and their principal tributaries from the valley terminus to tree line. Some sites were revisited during successive years, however, most were searched only once. Sighting data were sorted by drainage within the 4 watersheds in the park (Appendix). Site locations were resolved to the nearest 50 m by UTM coordinates determined from standard 7.5', 1:24,000 USGS quad maps. UTM and elevation data were processed via a Unix-based Sun SPARC IPX Geographic Information System (GIS) running GRASS, Version 4.1. Survey data were used to generate range maps for each species. Adjustments were made during GIS processing of location data to minimize errors in the generation of species range maps arising from habitat variability across similar elevations, and to accommodate special circumstances such as disjunct or geographically restricted species distributions. To deal with variable weather influences, exposures, and radically different microhabitats at the same elevation within a watershed, range maps generated by the GIS excluded the highest 5% of recorded elevations for most species. This adjustment was not made for painted turtles, Chrysemys picta, or Pacific treefrogs, Hyla regilla, because both species occupy restricted geographic and altitudinal ranges in the park. The range map for tailed frogs, Ascaphus truei, includes only streams with documented sightings, because this species occupies a highly disjunct range in Glacier National Park. Frogs and toads were collected with a telescoping capture net fitted with a 25 cm diameter bag of 5 mm mesh size. A small handheld dip net was used for capturing tadpoles and salamander larvae. Captured specimens were identified in the field (Stebbins 1985) and in some cases measured and released. Garter snakes were hand-captured for positive identification and released. Field data included location, weather, water temperatures, habitat types, proximity of fish, and developmental stage of specimens. Field work was limited to daylight hours from late May through September 1990 to 1992. Night searches were not made due to the presence of dangerous predators in the study area; occasional night observations were made opportunistically in the vicinity of back country cabins and field camps. Field investigations were supplemented by examination of specimens and collection records from the Glacier Park Museum. Thirteen other museums issued collection permits for herpetofaunal studies in Glacier National Park also provided data. Because the present survey was undertaken to assess current conditions, museum data were not incorporated into the GIS range maps. However, past sighting and collection records are discussed in the accompanying species accounts.