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| NATIVE AND INTRODUCED CALIFORNIA FISHES, 2005 CDFG |
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| Click Image Above to ENLARGE Details. |
The American Bullfrog (Rana catesbeiana):
was introduced to Western North America, and California in particular,
during the late 1800's (Hayes & Jennings 1994, etc.). The larval bullfrog (tadpole) pictured below, can take
at least 2 years and sometimes upto 3-4 years to transform, or metamorphosize, into a juvenile froglet (young, tailless frog),
also known as a "metamorph".
Bullfrogs require at least 1 meter of permanent water depth to breed in the spring and summer, are diurnal and nocturnal
and prefer warm vegetated banks and thick vegetation for cover. The water must last for at least 1-3 years for
tadpoles to metamorphosize. Aquatic Resource Specialists' herpetologist Bradford Norman is
a co-author on an up-coming paper on bullfrog predation habits and diet types at the San Luis National Wildlife Refuge
Complex, Los Banos, Merced County, California (Olds, et al., 2005), In press).
| Click Image to ENLARGE. |
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| BULLFROG TADPOLE - AN INVASIVE SPECIES IN CALIFORNIA COMPETING WITH NATIVE AMPHIBIANS. |
This specimen is a first year tadpole, no hind limbs yet. Hind limbs develop first and
fore limbs erupt just before metamorphosis (which ends when the tail is completely re-absorbed) (see Gosner, 1960,
Herpetologica for standard tadpole staging key).
The tadpoles can be at various stages of development in any given water body where they breed and
succeed, as the picture below illustrates. Over 200 can be collected alive in unbaited traps on the San Luis National
Wildlife Refuge Complex during the summer months, as the bullfrogs breed there in good numbers. Bullfrog tadpole numbers
and densities were especially high in Chester Marsh, Winton Marsh and Three Partners Ponds; tadpoles
were present in low densities in Sand Slough, Salt Slough, and Swan Lake; bullfrog tadpoles were absent from our San Joaquin
River mainstem sites in a Summer 2004 aquatic trapping study focusing on Giant Garter Snake (Thamnophis gigas), a Federally-listed
Threatened Species, and a California State-listed reptile species.
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| A Trap Full Of Bullfrog larvae, Summer 2004, Chester Marsh, San Luis National Wildlife Refuge, CA. |
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| CHESTER MARSH: BULLFROG LARVAE PARADISE IN CENTRAL VALLEY CALIFORNIA. |
Many adult bullfrogs were seen as road mortalities along Highway
165, which runs through the San Luis Refuge. At the newly constructed barracks, I was able to document at least
3 cases of juvenile bullfrog mortality in the parking lot. I saw at least 3 adult bullfrog mortalities on Wolfsen Road and
at least 6 adult mortalities on the main Highway 165 to Los Banos from the Refuge Barracks, and on the way to Turlock, across
the Merced River. These observations confirm the migratory nature of this species during summer nights, between canal
and along systems, ditches, ponds, and marshes in the San Luis Wildlife Refuge area.
| COMPARISON PHOTO FOR ADULT BULLFROG & RED-LEG FROG |
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| Click Image Above to ENLARGE Details. Credit: USFWS Protocol 2005. |
| Credit: Leonard et al, 1993. |
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| BULLFROGS CAN PREDATE ON NATIVE BIRDS AND FROGS. ETC. |
Click Here For a Web LINK to a U.S. Government Site on INVASIVE SPECIES - NATIONAL INVASIVE SPECIES COUNCIL
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