A day filled with frogs

Recently I helped Arthur (a friend in my lab doing Tadpole Ecology) out by assisting him in the field for a day. Basically we were inspecting various ponds that he is studying. We were walking the aquatic pond perimeters, searching for amphibians (measuring successful captures), and egg masses. At this time, the wood frogs (WF) and boreal chorus frogs (BCF) were in full chorus; bringing music to my ears (and deafening me at times). I had a lot of fun with Arthur and got to see things (associated with amphibians) that I have never seen before.

I was able to find Arthur a large patch of chorus frog egg masses. This was exciting because I have never seen BCF egg masses before. It was also exciting for Arthur because last year he didn’t see a single mass and now this year we found > 76! Arthur collected these egg masses and took them home to hatch so that he can perform an enclosure experiment. Unfortunately, most of these eggs have died L He will have to find the cause of this high egg mortality before he goes back into the field to collect more eggs.

After I found the BCF egg masses, I saw the largest gathering of wood frogs in my life. There were probable over 100 frogs in a 7 by 4 meter quadrate! It was surreal! Among these frogs was a WF egg mass nursery, containing well over 200 egg masses. The interesting thing here was that male WFs were actually crawling over the masses and sitting on them. You would think that this kind of interference would be stressful for the eggs. However, wood frog eggs are thought to be able to withstand various stress factors since they are laid in cold water which experience periodic freezing and thawing. I mentioned this to my supervisor, and she thinks that the male WFs may be sitting on the egg masses to provide deposit more sperm over them, hoping to fertilize ones that were unsuccessful the first time.

At this same location I saw my first wood frog mating ball. If you are not familiar with the term mating ball in amphibian biology, I will fill you in. It’s when you have a female in the middle and various (2 to >2) males attached to her. Males will be on her back, stomach, head, butt, etc, trying to successfully mate with her. Poor female! ;) In these mating balls, the female has a reduce chance of living.

What was really exciting about this ball was my ability to see the hind limbs of both sexes. As I got really close to examine this ball, I noticed the webbing on the female and male hind limb. The female had concave webbing while the males had convex. This is quite interesting because a couple years ago Arthur mentioned that he read that you can use this diagnostic feature to identify sexes in the off breeding season. However, during my 2005 field season, I looked for this trait but NEVER found it. I wonder, since I saw the webbing on male and females (in mating ball formation) in the water, water is the medium that allows the webbing to be distinct and in air the webbing isn’t as extended so the trait is masked.

During this trip I also got to see various raptors, bison (so cool), a dead porcupine (which was the first time I have ever seen one), ground squirrels, and lots and lots of amphibians. It was a fun and fulfilling day.