Friday, March 20, 2009

A Sign of Spring--Frog Eggs

Yesterday we stopped at a desert spring to look for frog eggs. Every March, Columbia spotted frogs (and northern leopard frogs) lay eggs in waterbodies in our valley. They are very picky about where they lay their eggs--the water has to be the right temperature, depth, and velocity. 

We looked around the edges of this spring. It has just warmed up, the trees are still bare, and we haven't seen many migratory birds, so it seems too early for frogs to be going about mating and laying eggs, but that's what they do.

We looked and we looked. In some places the algae was really thick on top of the water.

Eventually, we found some Columbia spotted frog (Rana luteiventris) egg masses. The egg masses can have from 150 to 500 eggs in them. One pair of frogs lays each egg mass, so the egg masses provide a good estimate of how many frogs are in the area--just count the number of egg masses and double it.

The black embryos develop into tadpoles in a few weeks, and then the hundreds of tadpoles swim out into the spring. Mortality is really high for the little tadpoles. They are a tasty snack for fish, birds, and garter snakes. Yet enough survive to keep the frogs thriving at this spring.

Columbia spotted frogs are known for their affinity to water. When they get spooked, they disappear under water. What is amazing about this spring is that it is a long way off from any other spotted frog locations, at least ten miles. So have the frogs here survived since much wetter times (like 15,000 years ago, when there was a huge lake that covered the valley bottom)? Or do the frogs get frisky and hop across the desert from time to time?

1 comment:

The Incredible Woody said...

I love listening to frogs. That is one thing I miss about our house in east Tennessee. We were near a pond and I loved to fall asleep listening to the frogs!!

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