Pseudacris triseriata (Western Chorus Frog) in Vermont
Jim Andrews and Mark Ferguson
Since its discovery in Vermont in 1975 the Western Chorus Frog (Pseudacris triseriata) has all but disappeared from its former limited range along Lake Champlain in Grand Isle and Franklin Counties. From a distribution that spanned six towns in two counties (see Vermont Herp Atlas map) it appears to be now limited to a few individuals at one site. For a period of thirteen years (1986-1999) it was not heard or seen at all. The two males heard calling during the spring of 1999 were not relocated in 2000. Although limited visits were made throughout the 1975 range of this species, the majority of the recent relocation efforts have been concentrated in the town of Alburg.
What follows is a brief review of our knowledge of P. triseriata in Vermont and our efforts to locate this species. It is a combination of the notes of Jim Andrews and Mark Ferguson and materials in their files. Additional efforts may have been made by Mark DesMeules, Chris Fichtel, Steve Parren or others over the past 15 years.
April 29 and 30, 1975: Fred and Paul Schueler, on a road survey of the distribution of P. triseriata from Syracuse, New York, through the St. Lawrence and Lake Champlain lowlands, hear the species in the towns of Alburg, Swanton, St. Albans, Highgate, Georgia, and North Hero, but not south or east of there. These data are not published (copies of field notes now deposited with the Vermont Herp Atlas). Five specimens from a grassy pond at the intersection of US Hwy 2 and Vt 78, 3 km SE of Alburg, are deposited in the Canadian Museum of Nature collection (CMN 16840).
1984: Francis Cook's review of The Reptiles and Amphibians of New England (Rudis and DeGraaf, 1983) points out the omission of Vermont P. triseriata in that publication. This is our first knowledge of this species in Vermont and of the Schueler records.
May 18, 1985: Mark DesMeules locates P. triseriata near the sites where Schuelers' specimens were collected. One male was observed and an estimated 12 were heard calling. This site is adjacent to a municipal landfill.
April 22,1986: P. triseriata were relocated at the same site by Mark DesMeules. Two males were heard calling.
May 4-June 9, 1988: A more intensive study of the Alburg area was conducted in an attempt to record additional occurrences of P. triseriata. Surveys took place on five dates: May 4, 12, 26, 31, and June 9. Twenty seven sites were visited, using recording to prompt calls. Roads were driven listening for frogs of any species calling. Stops were made where frogs were heard. Habitats included cattail marshes, temporary ponds, wet grassy swales, roadside ditches, floodplain swamps, and shrub swamps. Each survey date began and ended with a visit to the known chorus frog site. No P. triseriata were detected on any date or at any site, including the known site. It was noted during the 1988 survey that vegetative cover had been stripped from the edges of the marsh in 1986. The effect this had on the population is not known. Also, the landfill was closed in 1988 due to groundwater contamination. Mark DesMeules and Chris Fichtel wrote up a report of this effort. Others including Jim Andrews and Charles Johnson joined them occasionally in the field.
May 13-July 29, 1992: Jim Andrews and interns survey selected sites in Franklin County but do not locate any P. triseriata. Survey starts later than ideal but does overlap known calling times from the region. Report written for the Nongame and Natural Heritage Program.
April 19, 1996: Jim Andrews and Alan Coulter do night-time road surveys in northern Grand Isle County. No P. triseriata heard or seen.
April 23, 1997: Jim Andrews and Greg Hellyer do a night-time road survey in Alburg and Isle LaMotte. No P. triseriata heard or seen.
May 6, 1997: Nine sites in Alburg, including the original site, were surveyed by Mark Ferguson. Survey was again done by road, with potential sites identified from topo maps beforehand. No recording was used. No P. triseriata were heard at any sites.
May 1, 1998: Mark Ferguson surveyed five Alburg sites, including the original site, by road. (Weather was very warm (15-18 C) and clouds were moving in.) At a new location, at least two P. triseriata could be heard; however, the distance from the road was too great to be 100% sure. Time was 22:30 hr. The site was posted, so he was unable to access the site at that time.
May 12, 1998: After getting permission from the landowner to access the site, Mark Ferguson returns with Jim Andrews. Again, time was 22:00 - 23:00 hr. No P. triseriata heard at the apparent location where calls had been previously detected. Other areas in Alburg and the Lake Champlain island chain were also visited that night. No chorus frogs were detected.
July 30-Aug. 2, 1998: Jim Andrews and group of Audubon teenagers (Take PART) perform active searches at a few selected sites in Grand Isle. No P. triseriata heard or seen.
May 4, 1999: Mark Ferguson returned to his probable P. triseriata site to verify its presence. (The weather was warm (13-15 C), with overcast sky and light drizzle. The air was very humid.) He entered a small headwater portion of a larger hardwood swamp, surrounded on three sides by pasture and cropland. Two males were heard calling from different spots; both were under tussocks of grass, located in an open grassy pool with water approximately 30-50 cm deep. Attempts to spot the males using flashlights were unsuccessful; they were well hidden and moved to new locations when disturbed. Fortunately, this small patch of habitat and the associated swamp are fenced to exclude cattle, with a 8-20 m vegetative buffer.
May 6, 1999: Mark returned to the site and recorded two males calling to provide evidence of their presence. The original P. triseriata site was also visited on both dates. No males were heard calling there.
April 7-May 8, 2000: Mark Ferguson attempted to determine the calling period for P. triseriata in Vermont by repeated visits to the new site. Survey dates were April 7, 18, 20, and May 8. As in 1998 and 1999, weather conditions were good to excellent during these visits. The original site was visited each date as well. Although Spring Peepers, Wood Frogs, Northern Leopard Frogs, American Toads, and Gray Treefrogs were all heard calling, no P. triseriata were heard on any date at either site.
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