Amphibian Monitoring in the National Capital Region - 2007: A focus on lentic and lotic habitats

Mattfeldt, Sandra; Grant, Evan; Bailey, Larrisa

2007 amphibian monitoring report. This report describes ongoing amphibian monitoring efforts in the National Capital Region Network. Amphibian monitoring was initiated in 2005 and is currently concentrated in Chesapeake and Ohio Canal National Historic Park and Rock Creek Park, with stream (lotic) sampling also occurring in Prince William Forest Park. The objectives of the monitoring program are to develop an efficient long-term sampling design to: (1) describe the current distribution of amphibians and explore factors that may influence occupancy probabilities or distributional patterns, (2) determine if amphibian distributions are changing annually, and if so, explore whether occupancy changes are relate to habitat quality and (3) provide information to aid in the generating and testing hypotheses that differentiate among possible causes of long-term changes in the proportion of area occupied among species, habitats, and park areas. Here, we present analysis from 2005-2007 and describe our findings related to the first two objectives. We discuss our results in the context of the National Capital Region’s continuing amphibian monitoring program. We detected 13 amphibian species in each year of sampling 33 wetlands from the Potomac Gorge area within Chesapeake and Ohio Canal National Historic Park (CHOH). We found that detection probabilities were less than one and were related to water temperature or survey visit for most species. Initial occupancy estimates (ψ2005) ranged from 0.15 ± 0.06 (ψ± 1SE) for N. viridescens to 0.68 ± 0.09 for R. clamitans based on a model with constant initial occupancy, colonization, and extinction probabilities. All of the environmental and habitat covariates influenced initial occupancy estimates for one or more species, especially wetland hydroperiod. Hydroperiod was an important variable in initial occupancy estimates for seven of the eight species analyzed and in all cases, the influence was positive. This finding suggests that wetland hydroperiod is likely a limiting factor in determining the distribution of many of the wetland breeding amphibians found at CHOH. In addition to hydroperiod, wetland area and flooding potential also influence occupancy probabilities for some lentic amphibian. This is the only study we know of that demonstrates the negative influence that flooding may have on the probability of occupancy for two amphibian species: A. maculatum and R. sylvatica. The remaining covariates we explored influenced the occupancy probabilities of some species (e.g. Percentage canopy cover for P. crucifer and R. clamitans), but the relationships were not consistent among species, nor with our a priori hypothesis. While derived year-specific occupancy estimates for lentic amphibian species were relatively constant over the three years, the occupancy state did change among sites for most species (i.e. there was local turnover at sampled wetlands). Some sites were colonized and others failed to support breeding and/or foraging activity (i.e. went locally “extinct”).

Amphibian Monitoring in the National Capital Region - 2007: A focus on lentic and lotic habitats

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