Bullfrogs in the NBG 2013

After several years of observations, with a little funding from the Rhode Island Rivers Council I began a video project to record wildlife in Providence’s North Burial Ground, with an emphasis on the tadpoles in a little drainage swale near the maintenance building.   The Misadventures of an Urban Naturalist tells some of that story. There is also a larger and permanent pond in the burial ground, and it may be the best wildlife watching place in all of Providence The Bullfrogs of the larger pond were always of interest, but in some ways I used them as a back up, something else to focus on in case the drainage swale went dry and produced no tadpoles.  As I noted above, the larger pond has an abundance of wildlife, 3 types of heron, ducks, geese, cormorants, kingfishers, and swifts, as well as songbirds in profusion, muskrats, occasional otters, a growing population (from 6 to 14 over the last few years)  of painted turtles, several varieties of fish, and bullfrogs.
The size of the pond, the inaccessibility of various parts of the shoreline, and the murkiness of the water means that unlike the drainage swale certain parts of the bullfrog life cycle are inaccessible.  The most obvious missing piece is that I have never seen, let alone filmed, the early stages of bullfrog tadpole life.  Fowler’s Toads and Gray Tree Frogs complete their breeding cycle in one season.  They mate, the eggs are laid, the tadpoles develop and the frogs and toads hop away from the pond between May and August.  Bullfrogs overwinter as tadpoles the first year.  Bullfrogs mate later in the season, so the tadpoles are in the water from July until the following July.  I have never seen the newly hatched  tadpoles in the late summer.  They do not appear to swim near the surface close to shore, so I have no idea where they are.
What I do see of tadpoles is the tadpoles that have overwintered in the pond beginning in May, once the water warms up.  They float near the surface, swim around,  jump out of the water, and are generally visible nearly every day.  What gets my attention is the jumping, and the video that accompanies this essay reflects that fascination with jumping tadpoles, including the use of slow motion so the motion can be seen a bit more clearly.
In the spring, in addition to the tadpoles, there are the frogs that have overwintered.  I have a collection of shots of the various frogs that have overwintered, the rogues gallery.  There is nothing systematic about these shots, I take them when I find a frog in range,.  I know there are not very many frogs in the pond in the spring, but it would take a much more scientific approach than I can muster to actually determine the population size.
The transformation from tadpole to frog in early July is fast.  I have found only one shot that shows a Bullfrog tadpole with legs, in contrast to the abundance of footage I have of Fowlers Toads and Gray Tree Frogs with legs,   It seems like one day there is an abundance of jumping and milling tadpoles, the next day there are no tadpoles, but the shoreline of the pond is covered in small frogs.  To give some sort of reckoning of the new abundance I came up with the idea of capturing on film how many take off when I go near them.  I have shots from 2 locations, in the northwest corner of the pond near the outflow and looking north from the peninsula/point in the center of the pond on the western shore.  Slow motion is again used to show more details.
After the new frogs show up the herons become more common (Green and Night as well as Great Blue) and the population slowly dwindles under the predation until they go to sleep for the winter in the bottom of the pond, waiting for spring and the chance to do it again.  I retreat into editing, waiting for spring and a chance to see the pageant of life played out in a pond again.

 

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