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Wednesday, March 19, 2014

Wildlife Wednesday: Baja California Treefrog




Baja California treefrog in Comanche Creek 3/31/2013
Although the California drought has reached fabled proportions, recent rains and the persistence of nature remind us that we are indeed entering spring. The hillsides are turning green in all but the lowest San Joaquin Valley grasslands, flowers-though stunted- are beginning to show themselves, and where there is water amphibians are starting to appear. In honor of this last phenomenon, we have decided to dedicate this week’s Wildlife Wednesday to the Baja California treefrog (Pseudacris hypochondriaca).

Anyone who has spent time near western waterways, or watched a movie with a nighttime camping scene should be familiar with the treefrog’s “ribbit” call. It really is hard to beat a chorus of these animals serenading the night. One interesting fact about a treefrog chorus is that it will be initiated by one male, with the rest joining in (NPS). Aside from their sound, these frogs tend to be the most common amphibian found on Tejon Ranch.
http://www.californiaherps.com/frogs/pages/p.hypochondriaca.sounds.html

Until recently, the Baja California treefrog was not a recognized species and instead had been considered Pacific chorus frog (Pseudacris regilla), which got split into three species based on genetic analysis in 2006. Baja California treefrog became the southernmost Pseudacris in California, with Sierran treefrog (P. sierra) to the north and northern Pacific treefrog (P. regilla) occurring in the far northwest corner of the state. As the map below shows, Baja California treefrog can be found from Kern County south, while Sierran treefrog dominates the central-to-northern part of the state. P. hypochondriaca can also be found east into Nevada and northwestern Arizona. Apparently, a few individuals have made their way to Colorado via nursery plants (USGS). 
Image courtesy of Californiaherps. http://www.californiaherps.com/frogs/maps/pregillamap3species3.jpg


In addition to sound and range, the field observer will be able to identify Baja California treefrog by its appearance. Small in size (3/4-2in), this frog can be green, brown, or reddish. In darker individuals, it may be difficult to see the brown stripe across the eye and toward the shoulder. Some frogs may have a distinctive Y-shaped marking on top of their head. 

One amazing thing about this species is that it can change colors based on environmental conditions and nearby predators, such as bullfrogs (Lithobates catesbeianus). However, these animals are not chameleons. According to Western Reptiles and Amphibians, “[Baja California treefrog] May change from dark to light phase in a few minutes, but basic hue does not change. With darkening, a green frog becomes dark green and a brown frog dark brown.” (Stebbins 2003; 222) It is possible to see five individuals of this species that appear to have five different color variations, but they’re still all Baja California treefrogs. 

Baja California treefrog in Monte Field 3/15/2014. Note the dark stripe along the eye.

In the lower elevations and when the weather is moderate (not too hot or cold), Baja California treefrogs may be active at all times of the day. In fact, this species may be active year-round at lower elevations (California Herps). On Tejon Ranch, we have been seeing P. hypochondriacha throughout the San Joaquin Valley, and at a couple of the springs in the Antelope Valley. We expect to continue seeing these amazing amphibians through the spring and encourage all participants on our upcoming trips to spend some extra time near the waterways looking for treefrogs, toads, and other amphibians!


FOR MORE INFORMATION:
NPS Channel Islands P. hypochondriaca Factsheet: http://www.nps.gov/chis/naturescience/baja-california-treefrog.htm
USGS Nonindigenous Aquatic Species account: http://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=2781




REFERENCES:
Nafis, G. “Pseudacris hypochondriaca – Baja California Treefrog." 19 March 2014.
< http://www.californiaherps.com/frogs/pages/p.hypochondriaca.html>
National Park Service. “Baja California Treefrog.” 19 March 2014.
<http://www.nps.gov/chis/naturescience/baja-california-treefrog.htm>
Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.
USGS Nonindigenous Aquatic Species Program. “Pseudacris hypochondriaca.” 19 March 2014