Sunday, April 7, 2013

Ask the frog staff: How many tadpoles actually survive into adulthood?


Hi Mark. A frog friend and I were at the lily pond today and it was rife with tadpoles of various sizes and stages. Two questions:

1) It looked like the two ducks might be feeding on them ... do they?
2) How many tadpoles actually survive to frog adulthood?


— Christine C.

This particular topic has come up a lot recently, and one of our visitors beautifully photographed a heron eating a rather large bullfrog out of the lily pond in the Children's Garden. It was a graphic interaction, but demonstrates how vital amphibians are in food webs and one of the reasons we use to illustrate how important it is to keep amphibians around. Almost everything eats them, or their tadpoles, or their eggs ... or all three.  Many animals eat frogs exclusively (including some frog species!), and the herons at the Garden obviously love them. I have seen ducks eating tadpoles quite rapidly. In fact, my amphibian class last summer quantified how quickly different aquatic birds could consume tadpoles of different densities.

One of the main purposes of tadpoles (as primary consumers) is to convert plants into protein for other animals to then consume. That's at least one reason why most amphibians produce hundreds (or thousands) of tadpoles in a season. The thought is that out of all of that production, 2 will survive into adulthood to replace mom and dad.

The bullfrogs here at the Garden (like the one pictured below) all found their way here naturally and are hardly 'our' frogs ... They have chosen the Garden as their habitat to live and breed, and as in any habitat, nature prevails. Bullfrogs regularly eat other frogs, and also insects, lizards, birds, snakes (including rattlesnakes!) and small mammals. We are fortunate that the Garden provides a habitat for wildlife to persist amidst the urban landscape.

The incredible photographs posted below were taken by Jan Wendler, a frequent visitor to the Garden.

Heron snatches prey

The heron now has to rotate its prey to the proper orientation for swallowing (head first) Not an easy task without hands!

Thanks again to Jan, for all the wonderful photographs ...