Naturespeak A naturalist's view of the world

March 12, 2009

Polly Wolly Doodles Underway

Filed under: Uncategorized — wykes @ 9:03 pm

Spring Peepers and Chorus Frogs are traditionally the first of their kind to announce the seasonal turn from winter into spring. These diminutive amphibians often begin their vociferous breeding season well before the ice is completely off the ponds and marshes. They may be the first calling frogs of the season, but they are not the first active frogs of the season – that honor rightly goes to Bullfrogs and some Green Frogs. The adults of these two species remain in their restful hibernaculums well into the spring season, but their tadpoles remain active under the ice all winter.

Any question about the first tadpole of the season, like the equivalent question about the first Robin,  is basically unanswerable because you’d need to see the last one of the previous season before coming up with the correct answer.  They are with us through every month of the year. Because bullfrog tadpoles take multiple seasons to complete their development they have to spend at least one, and often two or three winters, in order to complete their conversion into adult frogs. Green Frogs hatched out after early July usually end up spending one winter as tadpoles before metamorphosing the following summer (earlier season hatchlings get the job done before winter just like all other local frogs).

I chalked up my first frog sighting of the season a few days ago as the ice finally released it’s prolonged grasp on the coastal marsh.  The silty bottom of the wetland teamed with wiggling Bullfrog tadpoles (see here in this video clip). I’m not sure what to call this gathering of pre-frogs  since “school” is a fish term and “pod” and “ipod” have already been taken. Given the makeup of the assemblage, I think a “herd” or a “doodle” would be appropriate. Saying that you’ve seen a doodle of pollies has a certain ring to it, don’t you think? Anyway, these pollywogs were going about their daily underwater duties as they have been doing all winter long.  Those doodle duties consist of swimming, feeding, and of course, breathing.

Structurally, Bullfrog tadpoles/pollywogs  are basically heads with tails (see above) .  As swimmers they are not quite up to fish status. Equipped with finned tails but no lateral fins or stabilizers, they are only able to propel themselves forward by vigorous undulations.  This creates a side to side rocking motion of the rotund body and head. The name pollywog, as a matter of fact,  comes from an American slang corruption of the old English term meaning “head wiggler. The mottled olive skin, large size,  and like-colored tails mark these individuals as Bull Frogs rather than the very similar looking Green Frog pollys.

The bull part of this species name refers to both the large size and the snorting call of the adults. The giant tadpoles can get to be 6 inches long, but as you can see they can be found in all stages of tadpoleness at this time of year.  All stages have equally ample appetites. Probably the best way to describe their  food habits is to call them opportunistic omnivores. Basically, this means they will eat anything from microscopic plants and diatoms, to dead animal matter and dead cousins. Zipperlike teeth enable them to scrape surfaces and even nip off live vegetation. Living under the ice through the long dark months of the cold season requires the ability to literally eat dirt at times! There’s no mystery as to why they become strict  predators upon becoming adults.

Perhaps the most remarkable thing about under-ice living is the ability to derive oxygen from the water even when the place is sealed over like a tomb. Young tadpoles are primarily gill breathers, but they can breath through their skin if need be. They also start lung breathing abut half way through the growth cycle.  One of their important adaptations consists of low or no oxygen respiration. The truth remains, however, that even in iced over marshes there are always a few air access holes provided by the friendly neighborhood muskrats! The ‘rats will enforce a fee for their services on occasion, and eat a few of the tadpoles. As a rule, Bullfrog tadpoles don’t taste very good so they are not hit hard by most predators.

One thing that remains clear as we consider these wintering pollywogs – tadpoles are neither delicate nor are they harbingers of spring. They are incredible examples of nature’s one upmanship ability over the seasons.

1 Comment »

  1. Hmmm, don’t wood frogs beat the chorus frogs to it? They’re explosive breeders (which brings all sorts of unsavory images to mind), mating only for maybe two weeks very early in the season. I’ve been doing Ann Arbor’s frog and toad survey for a few years, but it’s at night, by calls, so I rarely see my anuran friends!

    Comment by Monica — March 17, 2009 @ 11:56 am

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