Invasive Bullfrog

Day 278: I would not have thought I had it in me to dislike a frog, but Rana catesbeiana (American Bullfrog) has given me reason to re-evaluate my position. No doubt about it, this invasive species is impacting our native frog population as well as populations of other amphibians. In fact, they have even been reported to eat birds. They are wary and fast, active and predacious both day and night, sometimes coming onto shore to hunt. Aside from out-competing native species, this exotic may also be a vector (host) for diseases which affect native amphibs. The good news is that they are primarily a lowland species. This large specimen was observed outside Eatonville. To the best of my knowledge, they have not been reported inside the Park.

Bullfrog Blues

Day 175: As mentioned in an earlier post, the Bullfrogs invading local ponds and creeks can be quite varied in colour, ranging from brown through green, sometimes even aqua blue. The colour of any one frog may change over time as a result of exposure to increasing or decreasing amounts of light, not in response to its surroundings as was once believed. This change is effected in specialized cells and by the manner in which they reflect light. The transition may take weeks or months to occur. The specimen of Rana catesbeiana shown here is entering a blue phase, and if my Bullfrog census for this city park in Yelm is any indicator, the Herons certainly won't be singing the Bullfrog Blues for lack of a hearty dinner.

Rana Catesbeiana, Bullfrog

Day 164: As much as I love the froggy folk, I find it difficult to say anything nice about Rana catesbeiana, the Bullfrog which is outcompeting native frogs in a rapidly growing number of ponds and wetlands in the Pacific Northwest. This exotic ("non-native") species is easily identified by its large tympanum (eardrum), as large or larger than the eye. Color can be quite variable, brown to brownish-green, green, or in some cases, even blue. In size, Bullfrogs can measure up to 150 mm. from snout to vent. The female is capable of laying up to 6000 eggs in a single season. Native to the eastern portion of the US, Rana catesbeiana is considered a problematic invasive in Washington.

Rana Catesbeiana, Invader

Day 303: A master of concealment, the Bullfrog (Rana catesbeiana) is under consideration to be listed as an invasive species in the freshwater ponds of lowland western Washington. A prolific breeder, this species thrives in the near-stagnant murk of surface-water retention ponds and slow-moving ditches. The bullfrog is a hunter, and will consume any prey slower or smaller than itself, including other frogs, mice, young turtles and even small birds like ducklings or hummingbirds. It has been known to cannibalize its own species.

Some sources say that bullfrogs have contributed to the decline of native amphibian species, however, surveys indicate a reduction in amphibian population even in the higher altitudes where bullfrogs do not occur. If the bullfrog is not the prime suspect in the decline, it is certainly not making it easy for native frogs to gain ground.