GRAY TREEFROG
Hyla versicolor
 
INTRODUCTION
The gray treefrog is one of two arboreal frogs in Rhode Island. The other species capable of climbing trees, the spring peeper (Pseudacris crucifer), is much smaller and active much earlier in the year than the gray treefrog. Adults treefrogs are stout bodied and have long, deeply webbed toes with large terminal adhesive toe pads, which combined with a mucus secretion enable these frogs to climb vertical surfaces. The color of gray treefrogs varies according to temperature. In the warm summer months, adult gray treefrogs are typically silvery white with hues of light green, allowing them to blend in flawlessly with lichen-covered trees. In cool conditions, this species becomes a deep charcoal gray. These well camouflaged frogs spend the majority of their time well above the ground, making them difficult to observe; however, during the breeding season they can frequently be located by their loud thrilling call. According to Taigen and Wells (1985) choruses of gray treefrogs are one of the loudest measured for North America.
 
IDENTIFICATION

  • Adults are the only moderate-sized frog (about 2 inches long) with terminal toe pads in Rhode Island.
  • They are sometimes green, but typically an ashy shade of gray with mottled patterns of darker gray and black pigments.
  • The inner thigh and lower flanks have "flash patches" of brilliant yellow-orange mottled with black.
  • The skin is blanketed in tiny warts.
  • Recent metamorphs are a bright lime-colored green with darker green patterning; they are the only small frog that are bright lime green in Rhode Island.

    Sexual dimorphism
  • Females are slightly larger than males.
  • Males have dark throats; throats of females and juveniles are speckled with a few black spots.

 
SIZE

AGE / SEX
SVL (SNOUT-VENT LENGTH) (cm)
SAMPLE SIZE
AVERAGE
RANGE
Std. deviation
ADULT FEMALE
4.8
4.1- 5.7
0.5
15
ADULT MALE
4.6
4.0- 5.4
0.4
24
JUVENILE
NA
NA
NA
NA
METAMORPH
1.8
1.2- 2.5
0.3
44

AGE / SEX
MASS (g)
SAMPLE SIZE
AVERAGE
RANGE
Std. deviation
ADULT FEMALE
12.1
4.7- 19.7
4.5
15
ADULT MALE
9.3
5.3- 14.4
2.5
24
JUVENILE
NA
NA
NA
NA
METAMORPH
0.4
0.2- 1.1
0.2
44



 

 
RELATIVE ABUNDANCE
Rhode Island
Treefrogs are relatively common in Rhode Island. They were detected at 20% of 119 randomly-selected pond west of Narragansett Bay (Paton and Egan 2001).
Regional
In New England, gray treefrogs are widely distributed (Klemens 1993; DeGraaf and Yamasaki 2001). They are very cryptic, so are heard much more often than seen (Klemens 1993).
 
DISTRIBUTION
Rhode Island
Gray treefrogs are found throughout the state (Paton and Egan 2001).
Regional
Gray treefrogs occur throughout New England with the exception of the northern half of Maine (Davis 1999b). They were collected from sea level up to 518 m (1,700 feet) in the Berkshire Mountains of Massachusetts by Klemens (1993) and occur at higher elevations if habitat is suitable.
General
Gray treefrogs occur throughout the eastern United State and into parts of southern Canada. They range as far north as southern Manitoba and as far east as Kansas and Texas. Hyla chrysoscelis, the diploid progenitor of Hyla versicolor, is found throughout southern, southeastern, and central United States (Klemens 1993). The two species are largely allopatric (Klemens 1993).
 
HABITAT NON BREEDING
As their name implies, gray treefrogs are arboreal. They spend the majority of their time in trees and shrubs in both coniferous and deciduous habitats (Vogt 1981). While aloft, treefrogs can be difficult to impossible to spot, for they are extremely cryptic- as they blend with tree bark and moss and lichen coverings. Treefrogs are known stay in one tree for many weeks where food sources are abundant and cover from the hot sun is available in the foliage (Dickerson 1906).

During the winter, treefrogs hibernate on the ground under tree roots, rotten logs, rocks, or leaf litter (Davis 1999b). Treefrogs have the ability to manufacture their own type of "antifreeze" by producing glycerol. This trait enables them to survive temperatures as cold as -6°C (21.2°F ) (Davis 1999b).

Unfortunately, there is little information available on non-breeding habitat requirements for gray treefrogs.


Gray treefrog camouflaged


 
HABITAT BREEDING

Gray treefrogs prefer ponds with medium to long hydroperiods (semi-permanent to permanent) in deciduous woodlands (Paton and Egan 2001). In southern New England, Klemens (1993) found gray treefrogs in shrubs and red maple swamps, but they were also collected in grassy pasture ponds, quarry and sand pit ponds, and even in ponds surrounded by manicured lawns and housing developments. Paton and Egan (2001) found treefrogs using a similar variety of habitats. Klemens(1993) also collected individuals in sandy, xeric pine barren habitats, both at coastal and inland locations.

 
HYDROLOGY
Gray treefrogs prefer ponds with medium to long hydroperiods though they will breed in ponds with shorter hydroperiods (Paton and Egan 2001).

 
MOVEMENT CHRONOLOGY

Adult gray treefrogs start their migration to breeding sites in late April, with the majority of the animals arriving by mid to late May (Paton and Crouch In press). As with all other pond-breeding amphibians in our area, gray treefrogs only migrate to and from breeding ponds on rainy nights. However, this species is particularly difficult to monitor because they easily climb over drift fences. As is the case with spring peepers, gravid females and their male suitors are much more likely to be captured when immigrating to breeding ponds, than after females have deposited their eggs. Presumably the lighter females have an easier time climbing over the fences.

In Rhode Island, gray treefrogs metamorphs emigrate from breeding ponds from mid-July through early September (Paton and Crouch In press).


treefrog climbing over driftnet fence



 

 
REPRODUCTION
Gray treefrogs are one of the last frogs to breed in Rhode Island (only green frogs and bullfrogs breed later). Their breeding season extends from early May through mid-June, so they have a relatively prolonged breeding period. Males arrive at breeding ponds first and attract females with their loud, prolonged call. Males call during both the day and night, although intensive vocalizations occur only at night. Typically, males initially call from trees and shrubs at the perimeter of breeding ponds. Males will sometimes compete for the best perch sites (horizontal branches with minimal vegetation) by butting, kicking, shoving, or jumping on each other (Davis 1999b). As the night progresses, they climb down to the ground and head towards breeding ponds where they establish calling territories at the edge of the pond. Females, who do not call, are lured to the ponds about 1 hour after the chorus begins (Ritke et al. 1990). Females eventually select a male, approach him at a leisurely pace, and initiate amplexus with a nudge (Littlejohn 1958). DeGraaf and Yamasaki (2001) found that 20-35 days elapse between the first appearance of adults and the first eggs in ponds.
 
EGG MASS
Gray treefrogs oviposit eggs in shallow water near the shoreline (Hausfater et al. 1990). Females deposit from 1,800 to 2,000 bicolored- brown and yellowish- eggs (Wright and Wright 1949). The eggs are deposited in packets of 10-14 eggs that are attached to vegetation near the surface of the water (Martof et al. 1980). The small packets are widely distributed, and thus, are difficult to find. The egg usually hatch in 4-5 days (Davis 1999b).
 
LARVAE
Gray treefrog hatchlings are very small about 6 mm in length and are yellowish in color (Dickerson 1906). At this stage, they can quite easily be mistaken for a spring peeper tadpole (Pseudacris c. crucifer); peepers and treefrogs are the only two species in Rhode Island that have lateral eyes. Treefrogs tadpoles develop rapidly, so that in less than three weeks the tadpoles have not only reached maximum length but also have rear leg buds (Dickerson 1906). As large tadpoles, the treefrog has a bright, high-arching red tail- this feature makes them readily distinguishable, no other tadpole in Rhode Island has a red tail. The agile tadpoles tend to stay in shallow water, where they seek cover in vegetation. Metamorphosis typically occurs within 45-65 days (Wright and Wright 1949).

Gray treefrog tadpole

 
METAMORPHS



Young metamorphs are about 7 mm long and bright lime green- a very different coloration from adults. Metamorphs change quickly after transformation -they adopt adult colors and measure approximately 1.7 cm as they emigrate from breeding ponds (Paton et al 2000). In Rhode Island, they emigrate from breeding ponds from mid-July through early September (Paton and Crouch In press).

Gray treefrog metamorph

 
JUVENILES
Sexual maturity: Gray treefrogs mature in three years (Degraaf and Yamasaki 2001).
 
FOOD
Adults
Adults feed on small insects, plant lice, mites, snails (Davis 1999b). They forage in trees and on the ground (DeGraaf and Yamasaki 2001).
Larvae
Tadpoles are filter feeders, they trap suspended particles of phytoplankton, periphyton, and other detritus (Davis 1999b).
 
PREDATION
Adults
Adults fall prey to various vertebrates (Klemens 1993).
Larvae
Gray treefrog tadpoles are consumed by aquatic invertebrates (Klemens 1993).
 
CONSERVATION CONCERNS
Raithel (pers. comm.) believes that gray treefrogs are extremely sensitive to anthropogenic change, and local populations have been affected by habitat loss and fragmentation. Populations seem to be more common in large blocks of habitat. Because they often breed in permanent ponds, stocking these ponds with fish could have negative impacts on populations. Klemens (1993) discussed the decline of gray treefrogs in urban or suburban areas in Connecticut. Klemens generally found more ponds with treefrogs in rural areas of the state.
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