This past August OWCN was activated for an oil event at Toro Canyon Creek. For those who may be unfamiliar with the area as I had been, it’s a creek in the hills just north of Carpinteria. A year-round water source was created after an oil-water separator had been built back in the 1990’s to help contain an existing oil well seepage. This allowed the oil to be diverted to a tank and the separated water to feed the creek. When clean, I can imagine how incredible this small oasis could be and the wildlife it would support; however, when we were activated, much of it was filled with thick oil sludge.
While the initial animals recovered were found deceased in the oiled creek, we soon began recovering live animals, all of which belonged to 2 species of frogs (plus one Western fence lizard who happened to be in the wrong place during cleanup). These frog species, the Baja California Treefrog (Baja) and the California Treefrog are often found to be sympatric (found in the same geographic area with each other) in southern California.
Baja California Treefrog
The Baja California Treefrog was by far the most recovered at this event (89 out of 94 frogs). Prior to 2006, it was classified under one species known as the Pacific Treefrog, but was then separated into 3 separate species with the southernmost population becoming the Baja California Treefrog.
The name “Treefrog” isn’t very accurate as these frogs are more ground-dwellers of low shrubs and grasses, although like treefrogs they have the typical rounded toepads that make them excellent climbers.
It is a small frog up to 2 inches long that has many different color and pattern variations which can change in response to its background environment. The one distinguishing characteristic that does not change is the dark stripe that runs across the eyes. It is an ambush predator that feeds mostly on insects at night, waiting for prey to come its way before lunging and capturing with its sticky tongue.
During the breeding season from November to July, the frogs are found close to water sources, with the males becoming territorial. The male makes his calls usually at night to attract females, but sometimes during the day as well during peak breeding season. It is the most commonly heard frog in its range and the call (click to hear) that has been widely used in movies.
The lower recovered number of the other species, the California Treefrog, could have been attributed to their different preferred habitat. This species prefers boulder areas of which there was much less of. I would always be excited when we’d recover one of these because of the small area they inhabited, in hopes that we could help preserve their presence after the cleaning had been completed.
This frog is just a tad larger in size than the Baja. It has less color variation with a lighter brownish grey mottled pattern on top and a rougher skin texture with bumps on its back similar to toads you may be familiar with but having those rounded toepads of treefrogs. The lack of the eye stripe is the best way to tell them apart from the Baja; however, they sometimes can have a faint stripe, which in juveniles may be more distinct.
This frog prefers mostly boulder type areas for refuge and tends to move further away from water during fall and winter, becoming less active during the colder months. During the spring they return to the areas of water to breed but usually take 2 years to reach a reproductive age compared to just 1 for the Baja.
Observations from the Field
One interesting oil-related observation that was made during this event is that regardless of how oiled the frog may have been when captured, this visible oil almost immediately would slough away with its slime layer. Further investigation hopefully will be done on how much oil remains on them that cannot be seen and the effect on amphibians both short and long term.