This post serves as a follow-up to my earlier remarks about chorus
frogs that breed in the late winter and early spring months. By now, we are well into summer, which means
that the spring peepers and upland and Cajun chorus frogs are silent, but other
species of frogs are extremely vocal. Mississippi
is home to quite a few taxonomic families of frogs and toads, including
Ranidae, or the true frogs (such as bullfrogs and leopard frogs), individuals
of which are largely aquatic and can be found in ponds, lakes, and streams;
Bufonidae, or the true toads; Microhylidae, or the narrow-mouthed toads;
Pelobatidae, or the spadefoot toads; and Hylidae, or the treefrogs, a group
that encompasses the chorus frogs (including the spring peeper and the upland
and Cajun chorus frogs), as well as many other species that can be heard
calling right now. Let’s take a look at
some of these hylids.
Treefrogs are distinguished by the sticky pads at the ends of their
toes, which enable them to climb. They
are typically found in trees and shrubs near sources of water. In the southeastern U.S., one of the most
common species is the American green treefrog (Hyla cinerea). As its name suggests, this frog is typically
bright green. However, like other
treefrogs, it is capable of changing color to adapt to changes in temperature
and environmental surroundings. It
usually, but not always, has pale stripes running along its sides, and its skin
is very smooth. The call is a nasally quank
that carries for a good distance. Large
choruses of this frog can be heard in almost any wet, wooded area.
Another common species is the squirrel treefrog (Hyla squirella), a small frog
with a raspy call that is reminiscent of a squirrel’s barking sound. This extremely variable species may appear
almost any color from bright green to dusky brown, depending on environmental
conditions. At first glance, a bright
green specimen of the squirrel treefrog might be mistaken for a green treefrog. However, the squirrel treefrog is smaller and
always lacks the pale lateral stripes of the green treefrog. Squirrel treefrogs were formerly restricted
to the southern half of Mississippi, but have recently expanded their range
northward.
The next three species to be discussed, the common gray,
Cope’s gray, and bird-voiced treefrogs, can be visually separated from the
green and squirrel treefrogs by virtue of their bumpy skin. Like all treefrogs, they are more likely to
be heard than seen, so it is still a good idea to learn to recognize them by
their calls.
As their name suggests, gray treefrogs are frequently
mottled gray in color, although they may also be various shades of green or
brown—again, depending on temperature and habitat. The two species of gray treefrogs, common
gray (Hyla versicolor) and Cope’s gray
(Hyla chrysoscelis), look identical
and are impossible to distinguish from each other in the hand. This is due to the fact that one species, the
common gray treefrog, is thought to have diverged from the other, the Cope’s
gray treefrog. Interestingly, common gray
treefrogs are tetraploid, meaning that they have four pairs of chromosomes
(i.e., genetic material)—twice the usual number. Tetraploidy is fairly common in plants and
invertebrate animals, but it is not as frequently observed in vertebrates. While common gray and Cope’s gray treefrogs
cannot be reliably distinguished from each other by sight, they can be easily identified by sound. Both species have low-pitched trills, but the Cope’s gray treefrog’s call is faster and more snore-like than the
drawn-out trilling of the common gray treefrog. If you are a Mississippian, though, it's possible that you will not need to distinguish between the two, since the common gray treefrog may occur in only the northernmost sliver of the state: http://maps.iucnredlist.org/map.html?id=55687. The Cope's gray occurs statewide: http://maps.iucnredlist.org/map.html?id=55448.
Bird-voiced treefrogs (Hyla avivoca) look like smaller versions of gray
treefrogs. One quick way to identify
them in the field is to look at the ventral portions of their legs; unlike gray
treefrogs, which have bright orange skin in this area, bird-voiced treefrogs
have greenish-yellow. You should have no
trouble with identification if you hear the frogs, though; the whistling,
bird-like call of the bird-voiced treefrog is drastically different from the sounds
of gray treefrogs. Also, while you could
find gray treefrogs in almost any type of forest, bird-voiced treefrogs tend to
be most common in swampy woods, especially those containing cypress and tupelo
trees. This is one of my favorite frog
species in the state.
The pine woods treefrog (Hyla femoralis) and the barking treefrog (Hyla gratiosa) are two species
found in the deep southeastern portions of the U.S. Unfortunately, I have had few encounters with
either, and have heard pine woods treefrogs only in forests on the coast. However, a friend and mentor of mine has
heard that species as far north as Newton County, Mississippi, so it is
certainly possible to find them fairly far inland. They
have strange calls—perhaps best described as sounding like hyperactive Morse code messaging. The call of the barking
treefrog, on the other hand, is throatier in sound than the green
treefrog’s call. Choruses of this
species bring to mind—well, for me, anyway—hundreds of bouncing rubber balls. The barking treefrog frequently has dark
spots and is also noticeably bumpy-skinned, making it easy to distinguish from
green treefrogs. In the hand, pine woods treefrogs could be mistaken for squirrel treefrogs, but their inner thighs have rows of pale spots, unlike those of squirrel treefrogs.
The tiny, aptly-named cricket frogs are not technically treefrogs,
as they belong to the genus Acris. Nevertheless, they are hylids, and, like
their relatives, they can commonly be found in vegetation near water. Unlike treefrogs, cricket frogs tend to stay
very low to the ground. The southern
cricket frog (Acris gryllus) and the northern cricket frog (Acris
crepitans) are the two most
common species in the state. They are
similar in appearance, and their insect-like calls are also a bit difficult to
distinguish from each other. However,
the southern cricket frog has a raspier sound than the northern. Both of these tiny frogs can be found in
grasses and herbaceous vegetation near water.
So much for the adult hylids—but what about the earlier life
stages: eggs and larvae? Well, if you peer
into small ponds, woodland pools, roadside ditches, or potholes on old dirt
roads, you might be lucky enough to see these.
Frog eggs are in clusters, while toad eggs are in strings. Tadpoles may take a month or more to fully
metamorphose. May the summer months be
hopping!
Sources
Species Profile: Cope’s Gray Treefrog (Hyla chrysoscelis), Savannah River
Ecology Laboratory, http://srelherp.uga.edu/anurans/hylchr.htm
Species Profile: Pine Woods Treefrog (Hyla femoralis), Savannah River
Ecology Laboratory, http://srelherp.uga.edu/anurans/hylfem.htm
