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OF THE BCKCDB

northeastern Chorus Frogs
Pseudacris triseriata


[Pseudacris species]

Everyone hears little 'Peeper' frogs announcing the onset of spring, but many People don't realize that there are two species in some of these choruses. The call of the Spring Peeper, the only small Treefrog in most of our wetlands and ponds, is a single short whistled note. In some temporary pasture ponds, roadside ditches, gravel pits, flooded fields, and shrubby wetlands, the 'Peepers' are joined by 'Creakers' - Chorus Frogs - with trilled calls that sound like a thumb running over a cheap plastic comb.

Peepers used to be allocated to the huge paraphyletic genus Hyla, but now both species are put in the genus Pseudacris. Both are small brownish frogs with slightly enlarged toepads, but they can be distinguished by the cross-shaped mark on the back of the Peeper (hence its name P. crucifer), and the three lines, or series of spots, on the back of the Chorus Frog (hence P. triseriata). In Eastern Ontario, both begin to call at the end of March (plus-or-minus a couple of weeks) and continue through April and May. The eggs hatch within a couple of weeks and tadpoles transform by early summer. Chorus Frogs tadpoles are very susceptible to predation by fish, and the species cannot breed in ponds where fish live. Both Peepers and Chorus Frogs usually mature in one year and rarely live beyond three. They hibernate beneath logs or shallowly underground, and are freeze-tolerant.

[Pseudacris triseriata] [Pseudacris species] [Chorus Frog] [Pseudacris species] [Chorus Frog] [Pseudacris triseriata] [Pseudacris species]

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Monitoring Chorus Frogs as emblems of ecological health


Because Chorus Frogs embody the need for ecological connectedness on a local scale, and are so vocally conspicuous in the first burst of spring, we've nominated them as a totem of local ecological connectedness and 'rural character' in the Great Lakes basin. The habitat of Chorus Frogs strongly attracts human 'development,' but increasing human residences, industry, traffic, and services fundamentally change the effect People have on the land and water. There's no prospect of returning the Great Lakes (including St Lawrence) Basin to wilderness, but thriving Chorus Frogs will indicate a diversity of relatively benign and overlapping human uses for the land, in a landscape in which relatively undisturbed habitats provide homes for a wide variety of wild species.

Chorus Frogs are an easy totem to celebrate: just listen for the distinctive creaking calls wherever you go in the spring, and write down the location, habitat, time, temperature, and other species calling from the site. The next step is the big one - general public recognition that habitat modifications that either eliminate Chorus Frog populations or degrade the corridors between their habitats are 'bad,' while those that favour Chorus Frogs are 'good' - but we'll never take this big step until naturalists listen for and document the distribution of the spring 'Creakers.' You can miss a decline for a long time if you don't carefully delimit the sites you are considering. "They're still around." was just as ambiguous a report from the 1990s as "Oh they're everywhere!" was from the early 1970s.

In much of the Great Lakes Basin 2001 will likely be a good year to go after Chorus Frogs - if they were ever going to make a recovery it will be after last year's wet summer. And if we get a decent summer this year, we'd expect the recovery to continue. But on the other hand, if they continue to disappear, then the species may well be in regional decline.

In everything that follows, we assume that you know the calls of all local Anurans, and that you record and report every species that is calling from any site where you report any species to your local herp atlas. In addition to these general skills, there are two particular skills you'll need if you're going to contribute to this effort:

Skill 1: Be sure you know how to record a location to within 100 metres, by latitude/longitude or Universal Transverse Mercator (UTM) Grid, from a topo map or global positioning unit (including knowing how to specify which map datum [model of the shape of the Earth] the maps you use or coordinates you record are based on). This detailed geo-referencing is necessary if your records are to be unambiguously identifiable as coming from a particular place, even if your local atlassing scheme generally uses a 10-km square (Ontario), 1 degree cell (Quebec), 7.5-minute quadrangle (New York), or Town (Vermont) for analysis. The websites, at least, of most atlassing programmes skimp on this precision in favour of convenience, so you may have to struggle a bit via e-mail to find out how to insert these data into the atlas' suggested format. We (and the Ontario Herpetofaunal Summary) think that the Military Grid format of the UTM (explained on the margin of Canadian topo maps) is the easiest way to do this, though lat/long waypoints from a GPS unit are just as accurate and easy to use.

Skill 2: Be sure you won't be fooled by the trilled calls of Peepers. Any account of Chorus Frogs describes their trilled calls that sound "like a thumb running over a cheap plastic comb, starting at the large-toothed end and running up to the small-toothed end." Chorus Frogs call during the day as well as at night. When Peepers are calling during the day, in the cold, or in a territorial dispute, they can also trill, but with a more whistled, less comb-like, call than that of the Chorus Frog (it's as if the 'peep' has been lost in the triseriata side of the genus, and the trill has to do double duty for Chorus Frogs). But: you have to be carefully familiar with the calls of both species to be sure which is uttering some of the trilled calls. In an active chorus, the trill of the Peeper is often a combat signal between males who have gotten too close for comfort, but trills also seem to be 'warming-up' calls in the cold or daylight. Sometimes there are entire choruses of trilling Peepers that don't peep at all, and their calls must be identified by the subtly whistled rather than ratchet character of the individual notes in the trill. Trilling Peepers are a frequent source of error in careless auditors of Pseudacris choruses.

Here's a series of steps along the path of increasing commitment to Chorus Frog monitoring:

Step 1: document the location of populations: Because Chorus Frogs are mostly noticed during spring calling, and because they tend to call from discrete ponds or little wetlands, each place they call from pretty well represents a single population. You can put the location of the populations you hear on the public record by sending the records to your state, provincial, or national herp atlas - e.g. EMAN's Frogwatch, the Ontario Herpetofaunal Summary, the New York Herp Atlas (or State Museum), Vermont Herp Atlas, or the Quebec Herp Atlas,or to us (bckcdb@istar.ca - Eastern Ontario Biodiversity Museum, Box 1860, Kemptville Ontario K0G 1J0). In this way you'll be helping to accumulate records that will document changes if they do occur.

Record the time you listened, air temperature, wind and precipitation, sources of distracting noise, and all species of Anurans (Frogs, Toads, etc.) that were calling (or that none were heard). In our records we record all Anurans, Birds, and Mammals that we hear and all Amphibians and reptiles we see while we are listening. Intensity of calling is indicated by the Wisconsin calling index (Index One = individuals can be counted; no overlapping of calls, Index Two = Calls of individuals are distinguished, but some calls overlap, and Index Three = full chorus; continuous calls) or by counts of individuals. We listen at a site until we are satisfied that we have heard all calling anuran species, usually from 2-5 minutes, but sometimes as long as 10 minutes if there is a lot of noise. We record starting and finishing times of the visit; air temperature and wind, sky, and distracting noise are described at each stop.

Step 2: follow a listening strategy. The usefulness of records of Chorus Frogs in detecting changes in status depends on selecting the sites you visit in such a way that you'll be helping a future analyst, who will find your records embedded in the mass of an atlassing database, to detect a change in the occurrence of the species at sites in your area. The only detectable change to a thriving population is decline, so ideally the selection of sites should be unbiased, including by chance those with good, small, and nonexistent choruses, but this would be general anuran monitoring, not anything specifically directed at Chorus Frogs.

So, once you've heard Chorus Frogs at a site, continue to listen there in subsequent years, recording and reporting all the species you hear, so your records document loss and recolonization as well as occurrence.

Elements of a listening strategy may include:

1) keep listening at places where you've recorded calling Anurans in the past, in order to continue the series of auditions.

2) listen at as many places where you've previously heard Chorus Frogs as possible each year,

3) in the calling season drive slowly with the windows open and record every place you hear Chorus Frogs (adding these sites to the 'previously heard' list in (2),

4) Use Peepers as evidence of the absence of Chorus Frogs. Peepers may seem ubiquitous, so that there's little point in sending herp atlases records of every place they're calling, but since Chorus Frogs have longer calling hours than Peepers, a record of a Peeper chorus serves as an indication that you listened for Chorus Frogs but didn't hear any.

Step 3: Check all the places within a 15 km radius of your home that have been recorded in the past. For those who want to try something a little more ambitious, managers of the herp atlasses have offered to send observers lists of places within a radius of their home (or other central location) where Chorus Frogs have been recorded in their databases in the past, so an observer (strictly 'auditor') can recheck every place where the species has been known. Or even more ambitiously, all the places where Peepers have been recorded as well. The resulting new records would go back into the atlas databases, so that anybody doing an historical analysis would find repeated visits to the same site. Send your central co-ordinates to us at bckcdb@istar.ca, and we'll forward the request to the appropriate atlas.

Step 4: Write up your results. Just as you don't really understand anything until you've taught it to someone else, you don't really understand a situation until you've pulled together everything you know, and everything you can find out, tabulated, thought about, & analysed it, and written an account of it. Province- or region-wide analyses of data are important, but they don't replace local accounts of the changing fortunes of species, as observed by local observers. If you have accounts of changed status of Chorus Frogs, we can post them here with the papers presented at the meetings, and there are local natural history and herpetological society newsletters where summaries can be published. With the internet, 'experts' are as close as a block-and-copy, and in the more obscure branches of knowledge (of which we must admit 'Chorus Frog population status' is presently one), 'experts' are always glad to see anyone else taking an interest in the subjects dear to their heart, and to provide any help that they can. - F. W. Schueler - 10 March 2001