Paul Stephen Corn

Extinction of Montane Populations of the Northern Leopard Frog (Rana pipiens) in Colorado

Between 1973 and 1982 nine populations of the northern leopard frog in the Red Feather Lakes region of Larimer County, Colorado, failed to reproduce. These failures all resulted in extinction of the populations. One area formerly supporting a population was recolonized in 1980, but no frogs were observed at any of the nine sites in 1981 or 1982. Six of the populations went extinct because the breeding ponds dried up. The remaining populations were small enough to be susceptible to random events, but the nature of these events is unknown.

A COMPARISON IN COLORADO OF THREE METHODS TO MONITOR BREEDING AMPHIBIANS

We surveyed amphibians at 4 montane and 2 plains lentic sites in northern Col- orado using 3 techniques: standardized call surveys, automated recording devices (frog-log- gers), and intensive surveys including capture-recapture techniques. Amphibians were ob- served at 5 sites. Species richness varied from 0 to 4 species at each site. Richness scores, the sums of species richness among sites, were similar among methods: 8 for call surveys, 10 for frog-loggers, and 11 for intensive surveys (9 if the non-vocal salamander Ambystoma tigrinum is excluded). The frog-logger at 1 site recorded Spea bombifrons which was not active during the times when call and intensive surveys were conducted. Relative abundance scores from call surveys failed to reflect a relatively large population of Bufo woodhousii at 1 site and only weakly differentiated among different-sized populations of Pseudacris maculata at 3 other sites. For ex- tensive applications, call surveys have the lowest costs and fewest requirements for highly trained personnel. However, for a variety of reasons, call surveys cannot be used with equal effectiveness in all parts of North America.

Descriptive Risk Assessment of the Effects of Acidic Deposition on Rocky Mountain Amphibians

We evaluated the risk of habitat acidification to the six species of amphibians that occur in the mountains of Colorado and Wyoming. Our evaluation included extrinsic environmental factors (habitat sensitivity and amount of acidic atmospheric deposition) and species-specific intrinsic factors (sensitivity to acid conditions, habitat preferences, and timing of breeding). Only one of 57 surveyed localities had both acid neutralizing capacity 10 kg/ha/yr, extrinsic conditions with a possible risk of acidification- Amphibian breeding habitats in the Rocky Mountains do not appear to be sufficiently acidic to kill amphibian embryos

EVALUATION OF EPISODIC ACIDIFICATION AND AMPHIBIAN DECLINES IN THE ROCKY MOUNTAINS

We define criteria for documenting episodic acidification of amphibian breed- ing habitats and examine whether episodic acidification is responsible for observed declines of amphibian populations in the Rocky Mountains. Anthropogenic episodic acidification, caused by atmospheric deposition of sulfate and nitrate, occurs when the concentration of acid anions increases relative to the concentration of base cations, resulting in a decrease in acid-neutralizing capacity (ANC). However, because several natural processes can also depress ANC, monitoring pH and ANC alone cannot provide evidence that episodic acid- ification of amphibian habitats is anthropogenic. We examined published data on water chemistry from central Colorado and southern Wyoming for evidence of episodic acidifi- cation, and we also compared original water chemistry data to observations of amphibian breeding phenology at three sites in northern Colorado. There is limited evidence that anthropogenic episodic acidification may occur in high-elevation habitats in the Rocky Mountains, but there is no evidence that episodic acidification has led to acidic conditions (ANC <0) or that amphibian embryos are present during the initial phase of snowmelt when episodic acidification might occur. The declines of some amphibian species in the Rocky Mountains are more likely due either to natural or anthropogenic factors other than acidic deposition.

Low Prevalence of Chytrid Fungus (Batrachochytrium dendrobatidis) in Amphibians of U.S. Headwater Streams

Abstract Many declines of amphibian populations have been associated with chytridiomycosis, a disease caused by the aquatic fungus Batrachochytrium dendrobatidis (Bd). Despite the relatively high prevalence of chytridiomycosis in stream amphibians globally, most surveys in North America have focused primarily on wetland-associated species, which are frequently infected. To better understand the distribution and prevalence of Bd in headwater amphibian communities, we sampled 452 tailed frogs (Ascaphus truei and Ascaphus montanus) and 304 stream salamanders (seven species in the Dicamptodontidae and Plethodontidae) for Bd in 38, first- to third-order streams in five montane areas across the United States. We tested for presence of Bd by using PCR on skin swabs from salamanders and metamorphosed tailed frogs or the oral disc of frog larvae. We detected Bd on only seven individuals (0.93%) in four streams. Based on our study and results from five other studies that have sampled headwater- or seep-associated amphibians in the United States, Bd has been detected on only 3% of 1,322 individuals from 21 species. These results differ strongly from surveys in Central America and Australia, where Bd is more prevalent on stream-breeding species, as well as results from wetland-associated anurans in the same regions of the United States that we sampled. Differences in the prevalence of Bd between stream- and wetland-associated amphibians in the United States may be related to species-specific variation in susceptibility to chytridiomycosis or habitat differences.

Estimating Occupancy in Large Landscapes: Evaluation of Amphibian Monitoring in the Greater Yellowstone Ecosystem

Monitoring of natural resources is crucial to ecosystem conservation, and yet it can pose many challenges. Annual surveys for amphibian breeding occupancy were conducted in Yellowstone and Grand Teton National Parks over a 4-year period (2006–2009) at two scales: catchments (portions of watersheds) and individual wetland sites. Catchments were selected in a stratified random sample with habitat quality and ease of access serving as strata. All known wetland sites with suitable habitat were surveyed within selected catchments. Changes in breeding occurrence of tiger salamanders, boreal chorus frogs, and Columbia-spotted frogs were assessed using multi-season occupancy estimation. Numerous a priori models were considered within an information theoretic framework including those with catchment and site-level covariates. Habitat quality was the most important predictor of occupancy. Boreal chorus frogs demonstrated the greatest increase in breeding occupancy at the catchment level. Larger changes for all 3 species were detected at the finer site-level scale. Connectivity of sites explained occupancy rates more than other covariates, and may improve understanding of the dynamic processes occurring among wetlands within this ecosystem. Our results suggest monitoring occupancy at two spatial scales within large study areas is feasible and informative.

TAXONOMIC VARIATION IN OVIPOSITION BY TAILED FROGS (ASCAPHUS SPP)

Abstract Tailed frogs (Ascaphus spp.) oviposit in cryptic locations in streams of the Pacific Northwest and Rocky Mountains. This aspect of their life history has restricted our understanding of their reproductive ecology. The recent split of A. montanus in the Rocky Mountains from A. truei was based on molecular differentiation, and comparisons of their ecology are limited. Our objectives were to provide a range-wide summary of information on Ascaphus oviposition, compare some aspects of the reproductive ecology of the 2 species, and examine geographic variation in their reproductive traits. Reproductive ecology of the 2 species differed. Ascaphus truei had smaller clutches, oviposited later in the summer, and had a longer duration of oviposition than A. montanus. A greater number of communal oviposition sites were attributed to A. montanus. These ecological differences support the recent taxonomic revision of Ascaphus and suggest that different management strategies may be necessary for each species where conservation is a priority.

Breeding Chorus Indices Are Weakly Related to Estimated Abundance of Boreal Chorus Frogs

Abstract Call surveys used to monitor breeding choruses of anuran amphibians generate index values that are frequently used to represent the number of male frogs present, but few studies have quantified this relationship. We compared abundance of male Boreal Chorus Frogs (Pseudacris maculata), estimated using capture–recapture methods in two populations in Colorado, to call index values derived from automated recordings. Single index values, such as might result from large monitoring efforts, were unrelated to population size. A synthetic call saturation index (CSI), the daily proportion of the maximum possible sum of index values derived from multiple recordings, was greater in larger populations, but the relationship was not highly predictive.

Basking by adult boreal toads (Bufo boreas boreas) during the breeding season

Basking is a thermoregulatory mechanism by which some ectothermic animals increase their body temperatures by exposing all or some of its body to direct sunlight. Posturing or changing the angle of the body in relation to the sun can increase or decrease the thermal benefits (Brattstrom, 1979). Wet skinned animals, such as toads, are not directly affected by radiant heat exchange (Tracy, 1975; Hoppe, 1979) and are best able to influence their body temperature by behaviorally choosing microhabitats receiving solar radiation (Tracy et al., 1993). While not directly warming the animal, solar radiation warms the substratum and thereby the air near the substratum such that the animal is experiencing a microhabitat warmer than the ambient air temperature. Adult and juvenile toads (Bufo boreas boreas and B. canorus) living at high elevations in western North America are active diurally and have been observed to bask in direct sunlight during mid to late summer, after the breeding season (Mullally and Cunningham, 1956; Mullally, 1958; Campbell, 1970; Lillywhite et al., 1973, Carey, 1978). Summer basking has been documented for other high-elevation anurans, such as Rana muscosa (Bradford, 1984). Daytime breeding activity in a population of B. b. halophilus in southern California has been described by Mullally (1958) and amplexed pairs of B. b. boreas are commonly observed laying eggs during daylight (Campbell, 1970; Corn and Muths, unpub. data). However, basking by adult toads during the breeding season has not been described. Basking may have several physiological benefits (Lofts, 1984; Zapata et al., 1992) but increased exposure might increase the risk of predation by birds, which has been observed in this population (Corn, 1993). We observed basking toads (completely out of the water on emergent rocks and logs) at Kettle Tarn in Rocky Mountain National Park (Larimer County, Colorado; UTM Zone 13, 2810 m elevation) early in the 1995 breeding season. On 3 June from 0955 to 1100 h, we observed 10-15 adult male and three amplexing pairs of B. b. boreas basking (Fig. 1). We observed several other males and nine additional amplexing pairs in the water. The pond was free of ice but was completely surrounded by snow. The sky was clear and temperatures were recorded by thermistor thermometer single-channel data loggers placed at Kettle Tarn on 12 May. Air temperature (measured 10-15 cm above the substratum) was 11.9 C at 1030 h and water temperature (measured at a depth of approximately 10 cm) was 12.2? at 1000 h and 13.6? at 1100 h. Wind was undetectable.

Distribution Limits of Batrachochytrium dendrobatidis: A Case Study in the Rocky Mountains, USA

Knowledge of the environmental constraints on a pathogen is critical to predicting its dynamics and effects on populations. Batrachochytrium dendrobatidis (Bd), an aquatic fungus that has been linked with widespread amphibian declines, is ubiquitous in the Rocky Mountains. As part of assessing the distribution limits of Bd in our study area, we sampled the water column and sediments for Bd zoospores in 30 high-elevation water bodies that lacked amphibians. All water bodies were in areas where Bd has been documented from neighboring, lower-elevation areas. We targeted areas lacking amphibians because existence of Bd independent of amphibians would have both ecologic and management implications. We did not detect Bd, which supports the hypothesis that it does not live independently of amphibians. However, assuming a detection sensitivity of 59.5% (based on sampling of water where amphibians tested positive for Bd), we only had 95% confidence of detecting Bd if it was in ≥16% of our sites. Further investigation into potential abiotic reservoirs is needed, but our results provide a strategic step in determining the distributional and environmental limitations of Bd in our study region.