Boreal Chorus Frog, 

Pseudacris maculata


Other names for this frog include the Western Chorus Frog, Pseudacris triseriata. Adults reach 41 mm, while newly-transformed frogs are 10 to 12 mm.  Toe tips are not expanded, and the dorsal pattern of stripes may be incomplete or interrupted.  The white lip stripe is distinct, and the canthal streak extends through and behind the eye to the shoulder.  The pattern should distinguish this species from all other Arizona hylids.  The call is a slow, short rasping, with a rising inflection lasting 0.5 to 2 seconds.  The sound is like stroking the small teeth of a pocket comb.

The Boreal Chorus Frog ranges from disjunct populations that are found in southern Ontario, southern Quebec, northern New York, and northwestern Vermont.  Elevational range is from near sea level to 3,670 meters. The exact distribution and natural history of this undescribed chorus frog (see below) needs to be determined.  The species present in Arizona is a high-altitude species and occurs on the Mogollon Rim, in the White Mountains, and in the Chuska Mountains.

The Boreal Chorus Frog is a terrestrial, cold-tolerant frog that can survive freezing. Females deposit clusters of 20 to 100 eggs on vegetation in shallow water and may produce as many as 1,500 eggs in a season.

Habitat includes wetlands and meadows without moving water and adjacent upland habitats, where they may overwinter.  Periods of inactivity may be spent in water with dense vegetation, under objects on the ground, or in rodent burrows.  Breeding sites include marshes, rain pools, glacial kettle ponds, snowmelt pools, bog ponds, marshy edges of lakes and reservoirs, flooded areas, and other bodies of water with little or no current.  Breeding pools may be temporary or permanent and usually have aquatic or wetland plants or submerged terrestrial vegetation.

An examination of the phylogenetic relationships of the North American chorus frogs (Pseudacris) from 38 populations found Pseudacris triseriata had multiple ancestors (Moriarty and Cannatella, 2004).  The western populations of P. triseriata were related to the Boreal Chorus Frog, P. maculata.  Therefore, I am referring to this frog as Pseudacris cf. maculata, or the Boreal Chorus Frog, until somebody comes along and describes it as a new species or synonymizes it with an extant species.

skin behind the head.  Toe pads are small, but visible; webbing on the feet is greatly reduced and is absent between the fingers.  A white tubercle is present on the hind feet.  In adults the dorsum is tan-brown with dark brown spots, which sometimes fuse to form stripes.  Juveniles are pale green with scattered flecks on the dorsum. New metamorphs and juveniles are superficially similar in appearance to the Arizona Treefrog.  The call is a loud, low-pitched wonk, wonk, wonk, or quack, quack, quack that lasts 0.2 to 0.3 seconds.

The Lowland Burrowing Treefrog occurs from south-central Arizona southward into Mexico and along the Pacific coast to Colima, and west to central Jalisco and Michoacán.  It ranges from near sea level to about 1,500 m.  It lives in burrows in open mesquite grassland close to washes.  The species is part of the Sonoran Desert scrub and semi-desert grassland fauna.

This subtropical frog spends much of the year underground.  The paradox in its name hints at the story of a lineage of treefrogs that became subterranean during the dry season but could still exploit arboreal habitats when active.  The relatively small head, with the skin fused to the skull, is involved in an unusual behavior.  This is an adaptation for phragmosis, a behavior whereby the frog flexes its head to plug the opening to its burrow.  By closing the burrow opening with its head, the frog reduces water loss and the risk of predation.  It has robust limbs with long digits, and a single, large tubercle used for digging is located on each hind foot.  Beetles and orthopterans are important in the Biology, based on a small sample.

Reproduction occurs in temporary pools formed by monsoonal rains.  Sexually mature males have a heavily pigmented throat patch, and large, slightly bilobed     vocal sac.  The species migrates between aestivation sites and breeding sites.  In a monsoonal downpour near Guadalajara one night, JCM observed hundreds of these frogs moving across the road to breeding ponds.  During the day, it takes refuge in holes it excavates or in rodent burrows in hard clay soils, where the humidity is high.

Aestivating Lowland Burrowing Treefrogs form a transparent cocoon made from layers of skin (Ruibal and Hillman, 1981).  During cocoon formation, the frog is motionless, with all limbs folded tightly against the body.  The presence of the cocoon is not obvious, due to its close adherence to the body and its transparency. The cocoon is perforated at the nostrils but otherwise covers the entire body.  The cocoon skin softens when placed in water and the frog’s movements allow it to escape from the chamber.  Examination of a cocoon fragment revealed a multi-layered structure with a total thickness of 0.05 mm and about forty-three cell layers visible in the vertical section.  The cocoon allows the frog to better control water loss or water uptake during aestivation.