Alderleaf Wilderness College

Alderleaf Commons: Forum & Online Community

At Alderleaf, we have many native amphibian species appearing in healthy numbers.  As of last year, we first noticed a bullfrog had shown up in one of our ponds.  The bullfrog (Rana catesbiana) was a very large individual, and it likely overwintered in that little pond.  Bullfrogs are not native to the West coast, but have been extensively introduced.  They prey on many of native animals, including our native amphibians. 

Some people are very strongly against the bullfrog, and want to see it eradicated.  Although, bullfrogs by themselves are probably not responsible for the serious decline of many amphibians in the USA, they are an additional factor that might compound the more serious threats of pollution, introduced disease agents and habitat loss. 

They are legally hunted without a permit in WA state, and have no season or bag limit.  It so happens, bullfrogs are also good to eat.  The is part of what encouraged their introduction in the first place, since they are much larger and produce much bigger frog-legs for the market than any of our native West coast frogs.

Since at Alderleaf, we really want to do whatever we can to help support the health of native animals, we want to control the presence of bullfrogs on the property. 

Northern red-legged frog (Rana aurora) are a large, native species that is endemic to the moist, coastal forests and adjacent wetland habitats of the Pacific Northwest.  It has experience considerable decline in some areas.  They appear to be doing relatively well at Alderleaf.

I remembered that I had the opportunity during a wetland restoration project to compare the 2 species side by side.  It so happens I had a camera on me at that time.  Here they are...



These two frogs are likely close to the same age and definitely both juveniles.  Notice the differences between them.  The red-legged frog has a more pointed head, less upward angled eyes (eyes angle more directly to the sides), a pale line on the upper lip that runs to just behind the eye.  A flesh ridge runs from the back of its eye to its rump, on each side of its body.  Meanwhile, the bullfrog has more upward facing eyes, a less pointed face, and a ridge/fold of flesh that runs from behind the eye to the front of the foreleg.  No fleshy ridge on its back running from eye to rump.




Now, notice the distinct inner thighs and inner legs of the aptly named red-legged frog.  Notice how much paler the bullfrog legs appear. 

Though these 2 individuals look quite different from each other, they can appear much more similar in color especially in older animals. This can cause some confusion.

Views: 812

Replies to This Discussion

An effort to limit the spread of bullfrogs on Vancouver Island, BC is currently underway. Here is their page which talks about the red-legged frog:

http://web.uvic.ca/bullfrogs/page3.htm

Now if you wanna see some BIG bullfrogs on the same site, check here:

http://web.uvic.ca/bullfrogs/page4.htm

and here:

http://web.uvic.ca/bullfrogs/page4id.htm
Also found it particularly interesting how the pond edge habitat had a strong effect on whether bullfrogs outcompeted other native frog species. See the comparison at the bottom of the page:

http://web.uvic.ca/bullfrogs/page4impacts.htm
Here is a quote from a book recently published by the SEATTLE AUDUBON SOCIETY called Amphibians of the Pacific Northwest:

"A large size, a voracious appetite, ability to use human-altered aquatic habitats (including the ability to tolerate polluted conditions), a capability for moving long distances (more than 1.6 km), a number of eggs (per mass) much larger than any other amphibian and the potential to reproduce more than once annually would seem to make Bullfrogs a problem as an introduction to the Pacific Northwest. However, no regional studies to date have succeeded in clearly identifying Bullfrogs as a problem. Bullfrog traits allow them to do well in fish-rich, warm-water habitats. Human-altered habitats in the Pacific Northwest are often rich in introduced fishes and have warmer water. These conditions tend to disfavor native amphibians, so the effects that Bullfrogs may have on the native fauna are hard to distinguish from those of introduced fishes and other habitat alterations. Disentangling these effects remains a challenge to understanding the actual impact of the Bullfrog in the Pacific Northwerst."

I think this is a pretty enlightening paragraph. It is indeed difficult to figure out exactly what the effect of bullfrogs on our native fauna might be. After all, everything is connected and it is very difficult to isolate the effects of any one animal in a complex ecosystem.

I do think, however, that some habitats provide much better opportunity for bullfrogs to out compete native amphibian species. Specifically, lowland, warm-water areas with less or little shoreline plants as mentioned in the last link above.

I also wanted to mention that for those of you who have heard the myth that bullfrogs have no natural predators in the Pacific NW, think again! Adult bullfrogs are eaten by great blue herons, otters, mink, coyotes and larger bullfrogs. Young bullfrogs are eaten by garter snakes, kingfishers, and green herons. And... also eaten by humans! That is infact what originally brought bullfrogs to the Pacific NW region: farming for frog legs.

RSS

© 2017   Created by Alderleaf Wilderness College.   Powered by

Badges  |  Report an Issue  |  Terms of Service