The Rana Dilemma

Back in 2009, I noticed a large concentration of bullfrog tadpoles in the northwest corner of the Wetlands. The tadpoles were congregated around a pipe which drains the higher ground above, particularly the Red Wolf Enclosure. I didn’t know why the tadpoles were gathered in this location but speculated that it was due to either the concentrations of dissolved oxygen in the water, higher temperature, algal growth (their main source of food), or a combination of those things. Something had to be a draw in that little corner of the Wetlands. Although their seemed to be more algae growing near the pipe, the oxygen levels and temperature showed no significant differences from other areas of the Wetlands (thanks Trish).

In subsequent years there have been other concentrations of tadpoles at another drain pipe on the west side of the Wetlands as well as a mass of shiners (fish) in a patch of smartweed just off the boardwalk, also on the west side of the Wetlands. I’ve concluded, rightly or wrongly, that the concentrations of these two aquatic creatures are for security reasons, to get away from predators.

This year it’s tadpoles again, in the smartweed next to the Main Wetlands Overlook.

These tadpoles are nearly on dry land.

The fear of being eaten must be greater than the fear of drying out and wilting away, a large percentage of the tadpoles are out of the water on the muddy banks of the Wetalnds. However, I doubt that any of them will actually dry out, the heron, mergansers, and even the resident raccoons will probably get to them before they completely desiccate.

This is easy pickin’s for any predator that happens by.

The predators in the Wetlands know that the tadpoles are where they are, they are the reason they are there. The heron, mergansers and raccoons visit the area after hours, after all the people have gone home. As soon as the Museum closes the birds and raccoons move in. Even before I make my rounds to check that all visitors are clear of the area before closing each night, I see our predatory friends making their way over to the west side of the Wetlands. It must be difficult for them to wait the entire day for us humans to leave so that they can begin their feasting. Indeed, I often see them inching their way towards the buffet during open hours.

What heron, merganser or raccoon could resist this hardy stew? I’m even tempted.

The number of tadpoles will twindle with time as the various predators devour them. If you want to see what a mass of bullfrog tadpoles looks like in person, stop by the Main Wetlands Overlook and peek over the railing into the smartweed, you’ll see them wiggling around in the shallow water there.

Have fun!

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