Authors:
Robin E. Jung, USGS Patuxent Wildlife Research Center, 12100 Beech Forest Rd., Laurel, MD 20708, robin_jung@usgs.gov
Joseph C. Mitchell, University of Richmond, 28 Westhampton Way, University of Richmond, VA 23173, jmitchel@richmond.edu

Species list
Description of technique
       Field time components
       Office time
       Equipment
Things that could bias your counts
       Call saturation
       Call interference
       Equipment quality
       Extraneous noises
       Species misidentification
       Weather
       Time of year/time of day
       Habitat change
       Observer effects
Advantages and disadvantages
Approaches to analyzing your data
Existing protocols and programs using this technique
Estimates of variation of counts for this technique
Studies that have used this technique
Literature cited
Figures (this link and links below take you to another page)
       Figure 1: Froglogger photo
       Figure 2: Schematic of automated recording system with voice clock.
       Figure 3: Schematic of dual timer automated recording system with voice clock.
       Figure 4: Weekly species occurrence and relative abundance obtained by a froglogger.
       Figure 5: Monthly variation in diel calling pattern.
Send a comment on this technique (this takes you to another page)
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Note: Some western species of Ranids (e.g. Rana Subaquavocalis) call underwater and may rarely or never call above water. Even for those western species that call above water the calls tend to have low carrying capacity. Thus calling surveys are largely inappropriate for these species. Species whose names are in BOLD are species whose calling most often occurs only for a day or two after heavy rains (usually in mid- to late-summer in the southwestern United States).

Bufo alvarius, Colorado River Toad; Bufo americanus, American Toad; Bufo baxteri, Wyoming Toad; Bufo boreas, Western Toad; Bufo californicus, Arroyo Toad; Bufo canorus, Yosemite Toad; Bufo cognatus, Great Plains Toad; Bufo debilis, Green Toad; Bufo exsul, Black Toad; Bufo fowleri, Fowler's Toad; Bufo hemiophrys, Canadian Toad; Bufo houstonensis, Houston Toad; Bufo marinus, Marine Toad; Bufo microscaphus, Arizona Toad; Bufo nelsoni, Amargosa Toad; Bufo punctatus, Red-spotted Toad; Bufo quercicus, Oak Toad; Bufo retiformis, Sonoran Green Toad; Bufo speciosus, Texas Toad; Bufo terrestris, Southern Toad; Bufo valliceps, Gulf Coast Toad; Bufo velatus, East Texas Toad; Bufo woodhousii, Woodhouse's Toad; Acris crepitans, Northern Cricket Frog; Acris gryllus, Southern Cricket Frog (Florida and Coastal); Hyla andersonii, Pine Barrens Treefrog; Hyla arenicolor, Canyon Treefrog; Hyla avivoca, Bird-voiced Treefrog; Hyla chrysoscelis, Cope's Gray Treefrog; Hyla cinerea, Green Treefrog; Hyla femoralis, Pine Woods Treefrog; Hyla gratiosa, Barking Treefrog; Hyla squirella, Squirrel Treefrog; Hyla versicolor, Gray Treefrog; Hyla wrightorum (eximia), Madrean Treefrog; Osteopilus septentrionalis, Cuban Treefrog; Pseudacris brachyphona, Mountain Chorus Frog; Pseudacris brimleyi, Brimley's Chorus Frog; Pseudacris cadaverina, California Treefrog; Pseudacris clarkii, Spotted Chorus Frog; Pseudacris crucifer, Spring Peeper; Pseudacris feriarum, Southeastern Chorus Frog; Pseudacris maculata, Boreal Chorus Frog; Pseudacris nigrita, Southern Chorus Frog; Pseudacris ocularis, Little Grass Frog; Pseudacris ornata, Ornate Chorus Frog; Pseudacris regilla, Pacific Treefrog; Pseudacris streckeri, Strecker's Chorus Frog; Pseudacris triseriata, Western Chorus Frog; Pternohyla fodiens, Lowland Burrowing Treefrog; Smilisca baudinii, Mexican Smilisca; Eleutherodactylus augusti, Barking Frog; Eleutherodactylus coqui, Coqui; Eleutherodactylus cystignathoides, Rio Grande Chirping Frog; Eleutherodactylus guttilatus, Spotted Chirping Frog; Eleutherodactylus marnockii, Cliff Chirping Frog; Eleutherodactylus martinicensis, Martinique Greenhouse Frog; Eleutherodactylus planirostris, Greenhouse Frog; Leptodactylus labialis, Mexican White-lipped Frog; Gastrophryne carolinensis, Eastern Narrow-mouthed Toad; Gastrophryne olivacea, Western Narrow-mouthed Toad; Hypopachus variolosus, Sheep Frog; Scaphiopus couchii, Couch's Spadefoot; Scaphiopus holbrookii, Eastern Spadefoot; Scaphiopus hurterii, Hurter's Spadefoot; Spea bombifrons, Plains Spadefoot; Spea hammondii, Western Spadefoot; Spea intermontana, Great Basin Spadefoot; Spea multiplicata, Mexican Spadefoot; Rana areolata, Crawfish Frog; Rana berlandieri, Rio Grande Leopard Frog; Rana blairi, Plains Leopard Frog; Rana boylii, Foothill Yellow-legged Frog; Rana capito, Gopher Frog; Rana cascadae, Cascades Frog; Rana catesbeiana, American Bullfrog; Rana chiricahuensis, Chiricahua Leopard Frog; Rana clamitans, Green Frog; Rana draytonii, California Red-legged Frog; Rana grylio, Pig Frog; Rana heckscheri, River Frog; Rana luteiventris, Columbia Spotted Frog; Rana muscosa, Mountain Yellow-legged Frog; Rana okaloosae, Florida Bog Frog; Rana onca, Relict Leopard Frog; Rana palustris, Pickerel Frog; Rana pipiens, Northern Leopard Frog; Rana pretiosa, Oregon Spotted Frog; Rana rugosa, Wrinkled Frog; Rana septentrionalis, Mink Frog; Rana sevosa, Dusky Gopher Frog; Rana sphenocephala, Southern Leopard Frog; Rana subaquavocalis, Ramsey Canyon Leopard Frog; Rana sylvatica, Wood Frog; Rana tarahumarae, Tarahumara Frog; Rana virgatipes, Carpenter Frog; Rana yavapaiensis, Lowland Leopard Frog; Rhinophrynus dorsalis, Burrowing Toad

(above is from Species list of Amphibian Calling Surveys technique)

Male frogs and toads (anurans) use advertisement calls to attract females for breeding purposes. Anuran species can be identified by their unique vocalizations, and many monitoring programs and researchers use calling surveys to monitor anuran populations (see Amphibian calling surveys section). However, the frequency of calling survey data collection can be greatly improved by using automated recording devices (frogloggers). The first researchers to use frogloggers were Van Gelder and M. Hoedemaekers (1971), followed by Drs. Charles Peterson (Idaho State University, Boise, ID) and Michael E. Dorcas (Davidson College, Davidson, NC) (Peterson and Dorcas 1994).

The original froglogger design (Figs. 1-3) consisted of a stereo cassette tape recorder, solid state timers, a battery housed in a weather-resistant box (e.g., tackle box), and one microphone outside the box attached by cable (protected by soda bottle or other device) to record calls. Another microphone inside the box is used to record a voice clock announcing the time when each recording begins (Peterson and Dorcas 1994).

A froglogger can be programmed to automatically start and stop recording for intervals from a few seconds to a minute or more at specified times (e.g., every hour). With a single timer, the froglogger can record at specified intervals within a 24-hour period (Fig. 2). With two timers (one timer controlling the other), the froglogger can be programmed to record only during certain times of the day (e.g., sunset to sunrise) when anurans are most likely to call (Fig. 3). Although batteries are used most often, a solar panel can be connected to keep the battery charged. If the recording interval is set to record for about 12 seconds every hour and a 90 minute cassette is used, then the recorder can record calls for a week before tapes need to be changed or turned over. This results in a week-long recording session on a 45 minute tape. The only times a site visit is needed is to change the tape (or download sound files) and replace batteries if necessary, which can be done on a regular basis (e.g. the same time each week). Attention must be paid to recording the day and time of the start of a new week on the side of the cassette being used.

Typically frogloggers are placed in secure areas (or are hidden from view to avoid human disturbance) and chained to an immovable object close to potential anuran breeding wetland sites. Parris et al. (1999) noted that the closer the froglogger was located to a stream or wetland site (e.g., within 5 m), the better the detection of species at the site.

Once tapes are recorded, they must be listened to and the calls identified. In our experience, it takes about 1-1.5 hours to record the call data from a 45 minute tape, so planning must include adequate data accumulation time. Data collected from frogloggers can include documenting 1) species presence, 2) species abundance using calling codes (e.g. 0-3) like those used for Amphibian Calling Surveys, or 3) tallying call rates or calling intensity if identifiable on tape.

New improved froglogger designs are being discussed or implemented (e.g., using digital recording equipment such as a mini-disc with an Onset Tattletale 4-channel datalogger).

Initial setup:

• Constructing or purchasing froglogger
• Travel time to and from froglogger site
• Time to set up froglogger in secure site
• Time to set up or record weather and ancillary information

Survey:

• Travel time to and from froglogger site
• Change tape and battery as needed
• Reset timer, check settings, record start time on tape

• Recording data from tape
• Data quality assurance and control (data proofing)
• Data analysis
• Report writing

• Froglogger
• Casette Tapes or Digital Tapes
• Thermometer
• Automated Weather Dataloggers (e.g., HoboTemps, Hobo Rain Gauge, or Onset products)
• Watch

Things that could bias your counts

As with Amphibian Calling Surveys, an index to population size (e.g. calling index from 0-3 for each species detected) may also be collected from froglogger tapes. However, as the number of calling individuals increases over a certain threshold over which individuals can no longer be distinguished (calling index 3), calling saturation occurs. A calling index of 3 signifying a full chorus can represent a population size anywhere from 6 to hundreds or thousands of calling anurans at a site. Hence, calling indices and the problem of calling saturation can allow only a very rough assessment of changes in amphibian population abundance over time.

Call interference could occur if one species' call interferes with or obscures the detection of another, quieter species. A froglogger recording may not pick up a quieter species if a much louder species is calling at the same time.

The quality of the froglogger recording equipment, particularly the microphone, will affect the ability of the froglogger to record species at a site. Use a high quality microphone when possible and make sure that the voice clock is accurate and works well after heavy use.

Extraneous noises, such as trains, traffic, other animal sounds, etc., may either interfere with the detection of anurans calling on froglogger recordings or interrupt calling activity of amphibians. Extraneous noises can be recorded from the froglogger tapes, and if quantified, could be used as covariates in analyses (e.g. relating number of cars passing to calling frequency at a site).

If recording quality is not good, species identification of calls on the tapes may be difficult. We advise that a person well qualified in frog call identification be the one to identify the calls on the tapes. Recorded segments may have only one or two calls and vocalizations other than advertisement calls (e.g. release calls, aggression calls) may be overlooked by relatively inexperienced people.

Anuran species typically call more intensely during humid and wet weather (e.g., soon after rainstorms) during warm periods. Because frogloggers are timed to record at set intervals, they are able to document calling under all types of weather conditions. If frogloggers are simultaneously deployed alongside automated weather data collecting devices (e.g., Hobo or Onset products), anuran calling data can be correlated with weather data or weather data can be used as covariates in analyses.

Time of year:

Species call at different times of the year. If a particular species is targeted, we recommend employing the froglogger during the time of year when that species is expected to breed. It is also possible to record all frog species from the start of the calling season to the end to obtain information on call phenology and changes in community composition. The goal of the project and site access issues will dictate the length of time the froglogger is in use.

Time of day:

Species typically call at night, although some species (e.g., wood frogs, Rana sylvatica) will also call during the day (Crouch and Paton, 2000). Researchers using frogloggers have found that species show temporal partitioning in calling activity. For example, Mohr and Dorcas (1999) found in South Carolina that southern cricket frogs (Acris gryllus) call at all times during the day, whereas tree frogs (Hyla cinerea and H. gratiosa) call primarily during the early evening after sunset and true frogs (Rana catesbeiana and R. clamitans) call primarily during the early morning hours before sunrise. We have found that such variation changes with latitude and wetland site (J.C. Mitchell, unpublished data).

In order to assure recording all species at a site, we recommend that frogloggers are set to record for both a daytime interval and a nighttime interval.

Anurans will no longer be able to breed or call at sites that are destroyed (e.g. filled in, developed) or that do not have standing water present (e.g. during severe drought conditions). Researchers have documented different calling intensities of the same species at different but nearby wetlands, presumably related to differences in habitat (e.g., vegetation) at those wetlands (Mohr and Dorcas 1999).

Observer effects are no more problematic for this method than regular Amphibian calling surveys, although having a permanent record of calls allows for a greater chance of correct species identification.

Listening to tapes from frogloggers, one can test the ability of different observers to determine species and estimate the numbers by playing the same recorded tape to several people and documenting their differences.

Advantages:

• Because of their longer counting times and tenure at a site, frogloggers typically document more and rarer species than regular calling surveys (Corn et al., 2000). For example, a froglogger at one site recorded Spea bombifrons, which was not detected using regular calling surveys or intensive surveys, including capture-recapture techniques (Corn et al., 2000). Frogloggers have also been used to document the presence of gopher frogs (Rana capito), one of the rarest amphibians in the eastern United States, at sites in South Carolina (Whit Gibbons, pers. comm.). Bridges and Dorcas (2000) found that traditional manual calling surveys conducted between ½ hour after sunset to 1 AM failed to detect southern leopard frogs (Rana sphenocephala), which called primarily from midnight to dawn at their study site. Because frogloggers were set to record at intervals throughout the night, frogloggers detected this species.
• Frogloggers were better than larval seining surveys at detecting more species with less effort at wetlands (Mazanti 1999).
• Frogloggers were "robust in the range of conditions encountered in a survey, with no significant relationships found between temporal or spatial variation in their performance and weather or site conditions" (Parris et al., 1999).
• Researchers using multiple frogloggers can record calling anuran species at many locations simultaneously in a systematic fashion for long periods of time (e.g., entire breeding season) with minimal field effort. Calling data recorded in the same fashion at multiple sites by frogloggers allows for direct comparisons of sites under the same weather conditions. Frogloggers provide data on daily and seasonal (breeding phenology) calling patterns in anurans with minimal field effort. They also provide information on the size of the population (typically as an index of 0-3, see Amphibian calling surveys section).
• Froglogger recordings provide a permanent record of anuran calls. Similar to photographs or voucher museum specimens, recordings can provide irrefutable evidence or documentation of the presence of a species at a particular location and time.
• Frogloggers minimize observer error in species identification (Bridges and Dorcas 2000).
• Except when setting up a froglogger, frogloggers eliminate the "observer effect" (some frogs stop calling when humans approach a breeding site).
• Frogloggers require minimal field personnel effort (e.g., changing tapes and batteries on a weekly basis).
• Frogloggers based on the Dorcas and Peterson (1994) model are now commercially available (see http://www.bedfordtechnical.com).

Disadvantages:

• Only documents presence of frog and toad species that call above water unless underwater frogloggers are developed and used (i.e., would miss species such as the Ramsey Canyon leopard frog, Rana subaquavocalis).
• Depending on the location, density of vegetation, interfering noise, and acuity of the recording equipment used, frogloggers may fail to detect nearby species that call very softly and/or whose calls do not broadcast very far (Parris et al., 1999). For example, it is conceivable that a human listener may detect a species at a site if s/he were out in the field at the same time the froglogger is recording if amphibian calls are too faint to detect on the froglogger recording or if extraneous sounds interfere with the detection of that particular species' vocalizations on the recording. Acoustics greatly affect the quality of the calls on a froglogger tape and are very different from that heard by the human ear in the field. This problem is only partly compensated for by using a high quality microphone.
• Sometimes frogloggers are stolen, tampered with or destroyed by humans and other wildlife (e.g., bears, raccoons).
• The quality of the sound recording and the ability of frogloggers to detect species at a location are of course dependent upon the quality of the recording devices used (e.g., microphone quality and directionality, etc.).
• Sometimes frogloggers can malfunction. For example, Berrill et al. (1992) found that sensitive microphones failed to work during periods of high humidity. We have also experienced failure in the voice clocks.
• Extraneous noises including inclement weather (wind, rain) can mask frog calls on froglogger recordings (Parris et al., 1999). Heavy rain will severely hinder recording sessions.
• Many froglogger devices have been built and improved models are continuously being designed, though none similar to the Dorcas and Peterson (1994) model are available on a commercial level. Hence, researchers must contract out the construction of frogloggers or build their own. Titley Electronics sells an Eco-Pro Digital Audio Processor, which has been developed in conjunction with various Australian bird and frog researchers as a frequency-selectable, sound-operated device that performs a function similar to the AnaBat Bat Detector/Delay Switch combination, but for audible sound. If the unit is programmed into a 'Sample' mode, a single cassette can record a sample of calls every day for up to six weeks. Frogloggers based on the Dorcas and Peterson (1994) model are now commercially available (see http://www.bedfordtechnical.com).
• The cheapest froglogger can be built for approximately $300, but more expensive designs with digital recording exceed $1,000-$2,000. Hence, there is a substantial initial setup cost particularly if many frogloggers are deployed.
• Listening to tapes to decipher and collect anuran calling data is often time-consuming. It may take more than two hours for a single person knowledgeable in frog call identification to record data from a single 90 minute tape (Mitchell 2000). Attempts have been made to develop vocal recognition software to automate the process of collecting amphibian species calling data from froglogger tapes (e.g. Kinectrics (formerly Ontario Hydro Technologies), Laboratory of Ornithology at Cornell University, Titley Electronics), though none are currently operational or commercially available as far as we know. Also, the following web site provides details about the system designed by Taylor et al. (1996) for amphibian voice recognition: http://www.cse.unsw.edu.au/~andrewt/papers/frog_iaai96/frog_iaai96.html.
• In essence, a tape from a froglogger would have to be digitized into a computer sound file or the froglogger can be designed to record frog calls digitally. The digital sound file would then be played into a software program in a computer to identify the calling species of frogs. The software could be designed to eliminate extraneous sounds such as passing trains or traffic that might make it more difficult to recognize the anurans calling.
• Calling data does not confirm anuran breeding or recruitment success at the site.

Froglogger data are typically used to assess the simple presence or absence of an anuran species at a site. As with manual calling surveys, an index to population size (e.g., calling index from 0-3) may also be collected from froglogger recordings (see Amphibian calling surveys section). Estimating the number of calling males by listening to froglogger tapes is challenging and may not be appropriate (Berrill et al., 1999).

Froglogger data can be used to illustrate phenological patterns at single wetlands throughout one or more years or they can be used to assess species presence and relative abundance of calling males at a site for a short survey period (e.g. Figure 3). They are very useful for descriptions of 24 hour calling patterns and how such patterns change across time. One can use calling intensity (e.g., Bridges and Dorcas 2000) or number of calls per hour during the sampling period to describe diel calling patterns (Mitchell and Georgel 2001). The graph in Figure 4 illustrates how the hourly frequency of calls changes throughout the day and between two monthly periods for a summer-breeding ranid frog.

Many researchers have used frogloggers (see Literature cited section below), although few studies using this technique are published. A list of researchers that we know are using or have used frogloggers is below.

• Ross Alford, James Cook University, Queensland, Australia
• Juanita Constible, University of Victoria, Australia
• Steve Corn, USGS Rocky Mountain Environmental Science Center, Wyoming
• Ken Dodd, USGS Caribbean Science Center, Smoky Mountains and Georgia
• Michael Dorcas, Davidsonville College, North Carolina and South Carolina
• Gary Fellers, USGS, Pt. Reyes National Seashore, California
• Robin Jung, USGS Patuxent Wildlife Research Center, Maryland
• Joe Mitchell, University of Richmond, Virginia
• Erin Muths, USGS Rocky Mountain Environmental Science Center, Colorado
• Chuck Peterson, Idaho State University, Intermountain West, Idaho
• Lori Smith, J.W. Jones Ecological Research Center, Ichauway, Georgia
• Tracy Tuberville, Savannah River Ecology Lab, South Carolina

Not readily available from the literature. See Amphibian CV database for variation in indices or counts from manual amphibian calling surveys.

See Literature cited section below for details on these references.

• Bridges and Dorcas 2000
• Corn et al., 2000
• Holloway 1997
• Mazanti 1999
• Mitchell, 2001
• Mohr and Dorcas 1999
• Osborne and McElhinney 1996
• Parris et al., 1999
• Peterson and Dorcas 1994
• Seigel et al., 2002
• Van Gelder and Hoedemaekers 1971

Berrill, M., S. Bertram, D. Brigham, and V. Campbell. 1992. A comparison of three methods of monitoring frog populations. C. A. Bishop and K. E. Petit (eds.). Declines in Canadian Amphibian Populations: Designing a National Monitoring Strategy. Canadian Wildlife Service Occasional Papers 76: 87-92.

Bridges, A. S., and M. E. Dorcas. 2000. Temporal variation in anuran calling behavior: Implications for surveys and monitoring programs. Copeia 2000:587-592.

Corn, P. S., E. Muths, and W. M. Iko. 2000. A comparison in Colorado of three methods to monitor breeding amphibians. Northwestern Naturalist 81:22-30.

Crouch, W. P., and P. W. C. Paton. 2000. Using egg mass counts to monitor wood frog populations. Wildlife Society Bulletin 28:895-901.

Heyer, W. R. 1994. Recording frog calls. Pp. 285-287 in: Measuring and monitoring biological diversity: Standard methods for amphibians.

Heyer, W. R., M. A. Donnelly, R. W. McDiarmid, L. C. Hayek, and M. S. Foster (eds.). Smithsonian Institution Press, Washington, D.C.

Holloway, S. 1997. Survey protocols for the stream-breeding frogs of far east Gippsland: the application of habitat modeling and an assessment of techniques. M.S. Thesis, University of Canberra, Canberra, Australia.

Mazanti, L. E. 1999. The effects of atrazine, metalochlor and chlorpyrifos on the growth and survival of larval frogs under laboratory and field conditions. Ph.D. Thesis, University of Maryland, College Park, MD.

Mitchell, J. C. 2000. Amphibian monitoring methods and field guide. Smithsonian Institution Conservation Research Center, Front Royal, VA.

Mitchell, J.C., and C.T. Georgel. 2001. Seasonal and daily calling patterns of frogs on Fort A.P. Hill, Virginia: results from froglogger surveys. Final Report to Environmental and Natural Resources Division, Fort A.P. Hill, Bowling Green, VA. 48 pp.

Mohr, J. R., and M. E. Dorcas. 1999. A comparison of anuran calling patterns at two Carolina bays in South Carolina. The Journal of the Elisha Mitchell Scientific Society 115:63-70.

Osborne, W. S., and N. A. McElhinney. 1996. Status, habitat and preliminary observations on calling of the green and golden bell frog Litoria aurea on Bowen Island, Jervis Bay National Park. Australian Zoologist 30:218-223.

Parris, K. M., T. W. Norton, and R. B. Cunningham. 1999. A comparison of techniques for sampling amphibians in the forests of south-east Queensland, Australia. Herpetologica 55:271-283.

Peterson, C. R., and M. E. Dorcas. 1994. Automated data acquisition. Pp. 47-57 in: Measuring and monitoring biological diversity: Standard methods for amphibians. Heyer, W. R., M. A. Donnelly, R. W. McDiarmid, L. C. Hayek, and M. S. Foster (eds.). Smithsonian Institution Press, Washington, D.C.

Seigel, R. A., R. B. Smith, J. Demuth, L. M. Ehrhart, and F. F. Snelson, Jr. 2002. Amphibians and reptiles of the John F. Kennedy Space Center, Florida: A long-term assessment of a large protected habitat (1975-2000). Florida Scientist 65:1-12.

Taylor, A., G. Watson, G. Grigg, and H. McCallum. 1996. Monitoring frog communities: an application of machine learning. AAAI/IAAI 2: 1564-1569.

Van Gelder, J. J., and H. C. M. Hoedemaekers. 1971. Sound activity and migration during the breeding period of Rana temporaria L., R. arvalis Nilsson, Pelobates fuscus Laur. and Rana esculenta L. Journal of Animal Ecology 40:559-568.