The green tree frog, Hyla cinerea, found in extreme southern Illinois.
Over the last few years there has been increased concern about worldwide population declines and even extinctions of frog and toad species. Habitat destruction and degradation are clearly responsible in some cases, but the most alarming declines have occurred in relatively pristine environments, such as the rainforests of eastern Australia and the cloud forests of Costa Rica. Because these declines cannot be attributed to the direct impact of human activities, scientists have become concerned that one or more global factors, such as increased ultraviolet (UV) radiation or acid rain, might be adversely affecting all amphibians.
This problem was considered important enough that, in 1991, the Declining Amphibian Population Task Force (DAPTF) was formed. One of the first research priorities identified by the task force was to investigate whether the reported declines might actually be normal population fluctuations experienced by healthy amphibian populations. To distinguish between real global decline and normal fluctuation requires baseline population data for as many species as possible over several years. In 1996, protocols for long-term monitoring of amphibian populations were proposed by a group of scientists assembled by the Biological Resources Division (formerly the National Biological Survey) of the U.S. Geological Survey. These protocols, which included terrestrial salamander monitoring, anuran (frog and toad) calling surveys, aquatic surveys, western surveys, and amphibian atlassing, were designed to be carried out by volunteers using limited outside resources. Among these, anuran call surveys were field checked first because they had the fewest "bugs" to be worked out and were the most volunteer-friendly.
The green tree frog, Hyla cinerea, found in extreme southern Illinois.
The anuran call survey protocol requires that each participant drive an assigned route in daylight, before the start of frog and toad breeding season, and locate 10 "stops." Each stop must be a wetland or potential amphibian breeding habitat, a minimum of 500 meters (0.3 miles) from each other, and a maximum of 200 meters (0.12 miles) from the road. Once 10 stops are established, the volunteer drives the route at night and records frog calls for a specific amount of time at each stop. The data collected for each route would be analyzed every five years to document amphibian population fluctuation.
The protocol stressed that randomly chosen routes are vital to statistical rigor of the program. However, I was concerned that some of the randomly chosen routes would fail to include a sufficient quantity of potential amphibian breeding habitat in some highly agricultural areas of the state. This is a problem because "failed routes" will not keep the interest of the volunteer and participation will drop rapidly. In addition, routes without enough stops do not add any information toward the goal of the survey: to establish baseline amphibian population levels. I decided to enlist the help of Illinois Department of Natural Resources Natural Heritage biologists and evaluate the randomly chosen routes in Illinois to see if these concerns were real.
In our study, 14 different field personnel evaluated 75 call routes. The recording of stops was standardized as much as possible by choosing the type of habitat at a stop from a list of wetland types. This procedure was followed until 10 stops were recorded or 30 km (20 miles) had been traveled for each route.
Eight of the 75 routes failed: 2 routes did not have any potential amphibian habitat because they went through big cities, 2 routes had to be terminated before 10 stops were reached because of road conditions, and 4 routes did not have 10 qualifying stops within our predetermined reasonable driving distance (30 km) because of agricultural practices. This level of success, 89%, is higher than we expected based on our experience with amphibian breeding habitat throughout most of Illinois. It provides the motivation we need to take the anuran call surveys in Illinois to the next level: gauging volunteer interest. If anuran call surveys sounds like something you would consider undertaking, send a letter to:
Chris Phillips
Illinois Natural History Survey
Center For Biodiversity
607 E. Peabody Drive
Champaign, IL 61820
Christopher Phillips, Center for Biodiversity
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