Tuesday, June 10, 2008

Amphibians of the San Gabriel River

Amphibians (frogs, toads, and salamanders) are just one group of animals found along the San Gabriel River. These fascinating creatures typically spend part of their life in the water and part on land although, as we will see, there are exceptions to this biphasic life style. Male frogs call during the breeding season to attract females and each species has a unique call. Summer nights along the river are often filled with the melodious calls of frogs and toads. Listed below are a few of the amphibians that can be found along the San Gabriel River.

Georgetown Salamander
The Georgetown salamander (Eurycea naufragia) is a spring- and cave-dwelling salamander that occurs only in the San Gabriel River basin in Williamson County—it is found no where else in world. Brownish in color, the salamanders are shy, usually hiding under rocks or leaves. Adults are only about 2-3 inches long. Unlike most amphibians, the Georgetown salamander is unable to live out of water and is entirely aquatic throughout its life. We know of its presence at only about a dozen sites along the San Gabriel. The Georgetown salamander is currently a candidate for listing as an endangered species, which means that some people have proposed that it be added to the endangered species list, but it has not yet been listed as endangered by the US Fish and Wildlife Service.

Northern Cricket Frog
The northern cricket frog (Acris crepitans) is the most common amphibian found along the San Gabriel River. Its call, which sounds similar to knocking two stones together, can be heard at all times of day and night in many places on the river. Adult cricket frogs are very small—only about an inch long in body length—and vary in color and pattern; many are gray or brown with greenish spots. The frogs frequent rocky shores and vegetation along the shores of the San Gabriel.

Green Tree Frog
Green tree frogs (Hyla cinerea) are one of the most beautiful amphibians on the San Gabriel River. Adults are usually about 1 to 2 inches in body length and bright green, with a white strip running down each side. Their toes have small suction cups that allow green tree frogs to climb reeds, bushes, and small trees near the water’s edge. Green tree frogs have a distinctive call that sounds somewhat like a goose honking. They often call in large choruses among reeds in shallow water, their calls filling the night air and traveling long distances.

Rio Grande Leopard Frogs
Rio Grande leopard (Rana berlandieri) frogs are found on western portion of the San Gabriel. Adults are green or brown with large spots, giving rise to the name leopard frog. The call of the Rio Grande leopard frog sounds like a snore, often punctuated with one or more squeaky grunts. These frogs breed over an extended period, in spring, summer, or fall following warm rain.

Southern Leopard Frogs
Southern leopard frogs (Rana sphenocephala) are cousins to the Rio Grande leopard frogs; the two species are very similar in appearance, but their calls are easy to differentiate. While the Rio Grande leopard frog’s call is a snore, the southern leopard frog sounds more like a laugh. Both species often add a squeaky grunt to the end of their call. The southern leopard frog is a more easterly species and it is most often found east of Georgetown on the part of the river that passes through the Blackland prairie. The southern leopard frog breeds in late winter and spring, although it can sometimes be heard well into the summer months.

Gulf Coast Toad
The most common toad of central Texas, the Gulf Coast toad (Bufo nebulifer) is found in a variety of habitats, including rivers, ponds, roadside ditches, and urban neighborhoods. These toads are usually 2 to 4 inches in body length and brown or gray, with dark strips running along each side. Its call is a long trill, lasting 2-6 seconds. It can often be heard along the San Gabriel after late spring and summer rainfall.

Cliff Chirping Frog
The cliff chirping frog (Syrrhophus marmockii) is unusual in that it lays its eggs on land. The tadpoles complete development within the egg and little miniature frogs hatch from the eggs. The cliff chirping frog is confined to the Edwards Plateau of Texas. Adults are usually ¾ to 1 ½ inch in body length and greenish, mottled with brown. The frogs inhabit cliffs and rock crevices along the river. They are especially common below the dam at Lake Georgetown, living in and among the large rocks used to construct the dam. The call is a bird-like chirp that sometimes becomes a short trill.

Bull Frog
The largest frog of central Texas, the bull frog (Rana catesbeiana) prefers slow and deeper water. It can be found along the San Gabriel where the water has been deepened by low-water dams. Usually light or dark green, this species is easily recognized by its large external ear drum. Its call is a series of slow, deep, vibrant notes that sound like “jug-o’-rum”.

My students at Southwestern University and I are currently conducting surveys of frogs along the north San Gabriel River between San Gabriel Park and Lake Georgetown. Our goal is to better understand how increasing urbanization of the river corridor affects the frogs and toads found there.


Mahlon Arnett said...

Found a Gree Tree frog on our porch. We are about1.5 to 2 miles from the San gabriel River - do have two ponds. Are these frogs common travelers, found all over is is he just an adventurer?
We have Leopard frogs, toads, Spring Peepers and others here. Beautiful choras at night. Once in a while a Bull frog shows up too.
Mahlon Arnett

Ben Pierce said...

Thanks for your interest in the blog. Green tree frogs are fairly common in this area, particularly east of I35. They often occur in ponds and along creeks, so the one on your porch might not have come from the river. I suspect it might be from your ponds. Do you hear them calling at night? They sound kind of like geese honking.

I am interested to hear all the frogs you have on your property. You may not have spring peepers--this is a little far west for them. You might be hearing Strecker's chorus frog, which sounds somewhat similar to peepers. Strecker's chorus frogs usually call in early spring--January, February, and March, sometimes as early as November or December if it rains and is warm. If you do have peepers that would be very interesting.

Kyle said...

When we were getting rid of our pool there was about 300 tadpoles in it. I could only save about 30 to 40 in a green bucket. I live about a 15 minute walk from the san gabriel river. they are a dark green to a muddy brown color with a few tiny dots on them.

Ben Pierce said...

Hard to say what these tadpoles are without seeing them. If they are fairly large, they probably hatched from eggs last fall and are most likely one of the leopard frogs, most likely the Rio Grande Leopard frog. How long were they in your pool and how big are they?