Minnesota Frog and Toad Calling Survey 99

Would you like to get involved in surveying frogs and toads in Minnesota? Scientists and herpetologists would like to get a more precise idea of the numbers of each frog and toad species in the state. This will enable them to look at population densities over time and determine whether populations of specific species are declining or increasing on a local and state-wide basis.

Background and Purpose:
Minnesota is home to 14 species of frogs and toads. In recent years many observers have been concerned with the decline of amphibians worldwide and frogs and toads in the Midwest. Wisconsin has had a frog and toad survey for the last fifteen years. The original Minnesota survey was copied from the Wisconsin model. The Minnesota Frog and Toad survey has been modified to adapt to the national standards set by the North American Amphibian Monitoring Program (NAAMP). The Wisconsin survey has shown that the concern is for the ecosystems as well as the individual species. Frogs and toads are sensitive to changes in water quality and adjacent land uses, so changes in their populations can serve as indicators of environmental quality.

The Minnesota frog and toad survey was initiated to increase the knowledge of frog and toad abundance and distribution, and to monitor population changes in the state. The NAAMP has developed a series of route maps. Each preassigned route consists of 10 wetland sites, which are visited 3 times annually (early spring, late spring, and summer), by volunteer observers. At each site the observer identifies the species present on the basis of their breeding season calls and makes a simple estimate of abundance of each species, using "call index" values of 1, 2, or 3. Miscellaneous observations are also solicited from other than permanent survey routes.

Establishing a New Survey Route
When you have received a new route that has never been run, it must be 'groundtruthed' before the actual survey takes place. First, locate the route on the Minnesota map (shown below) and drive to its starting point. Next, you look around the starting point to see if there is a potential amphibian breeding site nearby (within 200 meters of the road).

If the stop is indeed at a potential amphibian breeding site, then it is stop number 1, if not, then you would continue to travel along the marked roads until a place that has a potential breeding site can be seen in close proximity (200 yards) to the road. After marking number one on your map, you should travel to at least 0.5 miles (gauged by the use of a car odometer) until a second breeding site can be identified. This stop is marked number two and so on, until 10 stops are in place, described and marked on a map. Click on the map to see a larger version.

The total distance of the route will depend on the density of potential sites along these roads. In some parts of the country the route will be only 4.5 miles long. If you come to the end of your highlighted route without placing all ten stops, then simply continue on the direction indicated until all ten have been determined.

While the 'groundtruthers' are busy looking for sites, it is also important to make sure that the roads are appropriate for stopping along. If they are too busy, too dangerous, on private land, or poorly maintained, then the routes may be shifted to the nearest set of appropriate roads that travel in the same direction.

Try to include a variety of wetland types that represents the range of breeding sites available. Consider large vs. small, open vs. shrubby vs. wooded, stagnant vs. flowing, permanent vs. temporary, natural vs. artificial, and remote vs. agricultural vs. urban sites. Do not avoid ponds that dry up during the year, for they are often productive during spring. Do avoid swift streams, and deep or denuded shores of lakes.

Surveyors sometimes find that one or more of the sites originally chosen turn out to be unsuitable breeding habitat, or are poor sites because of unforeseen background noise, access problems, etc. In these cases it is usually necessary to replace the problem site with a new site sometime after the first survey run, thus voiding the entire first year's monitoring data. To avoid this, it is recommended that you begin with 11 or 12 sites for the first year and choose only the 10 most reliable sites for the permanent route. At the end of the first year, report results only for the 10 permanent sites.

Correspondence related to the Minnesota Frog and Toad Survey should be directed to:
John J. Moriarty, Coordinator Minnesota Frog and Toad Survey, 3800 County Rd. 24, Maple Plain, MN 55359

Describe your route
Mark the precise locations of your 10 sites on the assigned maps, and describe each listening point and wetland on the "survey route description" form. Sites should be numbered in a convenient route sequence. Return the maps and route description with your completed data forms by 1 September to Minnesota Frog and Toad Survey, MNDNR Nongame Research Box 25, DNR Building, 500 Lafayette Rd., St. Paul, MN 55155-4025

Enlist additional observers
Enlist one or more additional observers who will become familiar with the route and survey procedures, and who can run the route in the event that you are temporarily or permanently unable to do so.

1. Obtain and review instructional materials and data forms.
The main, designated cooperator for each established route will automatically receive these materials in late March or early April. Contact the coordinator if you have not received your packet by 7 April. Materials include: Instructions; Route map; Route description form; Field data sheets (2 copies); Misc. Observations form; Natural history information

2. Know the calls, phenology, and general ranges of Minnesota frogs and toads.
New and experienced observers will both find it helpful to review a frog and toad tape periodically, and to take it along during surveys to help identify uncertain calls. New observers can learn the calls gradually by starting with those species that may be calling during the early spring survey period (Wood Frog, Spring Peeper, Northern Leopard Frog, Western Chorus Frog, and Pickerel Frog), followed by those species that begin calling in late spring (the 3 toads, Northern Cricket Frogs and both treefrogs), and finally by those species that begin to call during the summer (Mink Frog, Green Frog, and Bullfrog). It is highly recommended that new observers practice distinguishing calls in the field with the help of a more experienced observer. Generalized distribution maps are attached. Additional information on frog and toad natural history is available in Amphibians and Reptiles Native to Minnesota by Oldfield and Moriarty. This book should be available at your local library or bookstore.

3. Run the route 3 times, once during each designated period.
The timing of the survey with the phenology of frog calling is essential. Data collected from outside the designated survey periods are difficult to interpret and impossible to compare between years or areas. In most areas, failing to make one of the 3 survey runs or failing to survey all 10 sites will severely limit or invalidate the entire year's data for monitoring purposes. Also consider minimum water temperatures, especially for the early spring survey period. The early callers may be variable due to the differences in snowmelt from north to south in Minnesota.

Survey Period Range of Dates Minimum water temperature
early spring April 15-30 10C (50F)
late spring May 20-June 5 16C (60F)
summer June 25-July 10 21C (70F)

In Minnesota, routes north of Highway 2 can add one week to the survey dates.

4. Run surveys after dark, under favorable conditions.
Choose an evening when water temperatures are above the minimums stated above and when wind is less than 8 mph. Warm, cloudy evenings with little or no wind and high humidity (even drizzly) are ideal. Humidity and cloud cover are not critical, but temperature is: a sudden drop in air temperature will cause most anurans to cease calling. If part way through a survey run you find that conditions deteriorate significantly ( e.g., rain begins, temperature drops, or wind increases), stop the survey and complete it at the nearest opportunity, within 2-3 days if possible.

5. Listen for calls at each site.
Approach a listening point so as to cause minimal disturbance. The arrival of a car or a person on foot may cause frogs to stop calling for a short time. When feasible (this is optional), during the early spring survey period, place a thermometer in the water near where the frogs are calling (don't forget to take it when you leave that site!!). Water temperature needs to be measured at only a few convenient sites during the later survey dates.

Listen for 3 minutes after the frogs start calling again. Listen to all calls audible from your listening point, not just those emanating from a particular pond, one side of the road, etc. Some calls may be drowned out by others, especially by the full chorus of spring peepers or chorus frogs. Where you suspect this to be the case, and after carefully listening and recording your initial data, you may try to silence the chorus by making a loud noise with horn, car door or voice; and then listen for the less conspicuous species as the calling gradually resumes.

A tape recorder will enable you to record questionable situations that can be listened to and confirmed at a later time or date. A sound parabola is helpful in isolating subtle call of individuals in a chorus of several species. Prescription hearing aids are helpful for listeners who have volume or frequency impairment.

6. Record your observations on the field data sheet.
Completely fill out the route identification information including county, route number, date, observers names and addresses, weather conditions, water temperature (if taken), time and additional comments on noise levels, attempts to silence loud choruses, changes in habitat since previous visits. Record the call index value for each species heard according to the following:

    1. Individuals can be counted with space between calls
    2. Calls of individuals can be distinguished but there is some
    overlapping of calls,
    3. Full chorus. Calls are constant, continuous, and overlapping.

7. Verify records of rare or extralimital occurrences.
Verification is required for Cricket Frogs and for records of other species found outside their previously documented range as indicated by the attached range maps. Verification can be accomplished by:
a) a tape recording, b) testimony of 2 experienced observers,
c) a photo, d) a specimen.
After an observer has verified the record, future records of the particular species in that area may not be required.

8. Return all materials by 1 September MNDNR Nongame Research. Make one copy of the field data sheets for your records. Mailing Address:
Minnesota Frog and Toad Survey, MNDNR Nongame Research Box 25, DNR Building, 500 Lafayette Rd., St. Paul, MN 55155-4025

9. Important! Maintain one or more alternate observers.
These observers should be able to produce results comparable to yours, should you not be able to run the survey temporarily or permanently. The alternates should accompany you on the survey periodically and be familiar with the calls, route, and procedure.

For more information on Minnesota Frogs and Toads click here.
An audio-tape of Minnesota Frogs and Toads Calls is available from the project at a cost of $12, which covers tax, shipping and handing. If you are interested in this tape, please send a check to Minnesota Frog Watch, MS-A1760, Hamline University, Graduate School, 1536 Hewitt Ave., St. Paul, MN 55104-1284. Make the check payable to Hamline University.

Barney Oldfield and John J. Moriarty produced a book entitled Amphibians and Reptiles Native to Minnesota (1994) soon to be available from the project. This excellent guide to the state's herps is invaluable to anyone interested in this topic and these animals.

Choose from these other areas:
Amphibian Facts
MN Frogs and Toads
Global Amphibian Declines
Malformed Amphibians
Surveying Populations
Malformed Amphibian Photos
Student and School Reports

If you have questions for our scientific experts, go ahead contact us by
(651-523-2987) or E-mail frogs@gw.hamline.edu


Thousand Friends of Frogs
Center for Global Environmental Education
Hamline University Graduate School of Education
1536 Hewitt Avenue, St. Paul, MN 55104-1284
Phone: 651-523-
2480 Fax: 651-523-2987
1999 CGEE. All Rights Reserved.

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