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GRAY
TREEFROG
Hyla versicolor
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| 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. |
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| 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.
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| SIZE |
| AGE / SEX |
SVL (SNOUT-VENT LENGTH) (cm)
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SAMPLE SIZE
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AVERAGE
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RANGE |
Std. deviation
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| ADULT FEMALE |
4.8
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4.1- 5.7 |
0.5
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15
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| ADULT MALE |
4.6
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4.0- 5.4 |
0.4
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24
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| JUVENILE |
NA
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NA |
NA
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NA
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| METAMORPH |
1.8
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1.2- 2.5 |
0.3
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44
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| AGE / SEX |
MASS (g)
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SAMPLE SIZE
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AVERAGE
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RANGE |
Std. deviation
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| ADULT FEMALE |
12.1
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4.7- 19.7 |
4.5
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15
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| ADULT MALE |
9.3
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5.3- 14.4 |
2.5
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24
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| JUVENILE |
NA
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NA |
NA
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NA
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| METAMORPH |
0.4
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0.2- 1.1 |
0.2
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44
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| 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).
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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).
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| DISTRIBUTION |
Rhode Island
Gray treefrogs are found
throughout the state (Paton and Egan 2001).
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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). |
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| 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.
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Gray treefrog camouflaged |
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| HABITAT BREEDING |
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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.
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| HYDROLOGY |
Gray treefrogs prefer ponds
with medium to long hydroperiods though they will breed in ponds
with shorter hydroperiods (Paton and Egan 2001).
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| 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).
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treefrog climbing over driftnet fence |
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| 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. |
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| 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). |
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| 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 |
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| METAMORPHS |
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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 |
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| JUVENILES |
| Sexual maturity: Gray
treefrogs mature in three years (Degraaf and Yamasaki 2001). |
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| 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).
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Larvae
Tadpoles are filter
feeders, they trap suspended particles of phytoplankton, periphyton,
and other detritus (Davis 1999b). |
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| PREDATION |
Adults
Adults fall prey to
various vertebrates (Klemens 1993).
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Larvae
Gray treefrog
tadpoles are consumed by aquatic invertebrates (Klemens 1993). |
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| 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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