The survival challenge that faces every American Bullfrog.
I captured this image last year. It is now May 14, 2016, and the bullfrogs have not begun to show on the same pond. And went May 20 and they still have not shown. They will begin calling within 1 week I think. That is when I will locate the first one of 2016.
Just checked last year's dates. This one was captured June 16, 2016. But the first bullfrog I photographed last year was on May 29, 2016. The aquatic vegetation is just beginning to emerge (May 14, 2016) and last winter was a exceptionally mild one, both in terms of snowfall and low temps. Most winters here on coastal Maine are much more severe than last year's. Of course, there might be no correlation between the two. But "ice-out" in southern Maine was very early this spring (late March). It usually occurs no earlier than mid-April and most often very late April.
The following is a short explanation for why the American Bullfrog really does live a precarious existence.
I have been watching these frogs my entire life. The spring-emergence of bullfrogs is quite closely synchronized with the emergence of aquatic plants. And the reason for this is that the frog must have the vegetation for escape cover. Here is why:
In the Food Web, American Bullfrogs are prey to the Great Blue Heron (GBH), both NA Bass species (Mycropterus spp.) and less occasionally the Snapping Turtle. But overwhelmingly, its greatest danger is the GBH. A bullfrog in the open is easy prey for the ever-present GBH. At their best, bullfrogs have a poor escape mechanism. Even within the cover of aquatic vegetation, I have always found that any frog is easy to spot and catch-by-hand after it has just submerged. This is for two reasons. The bullfrog lives in very shallow water, immediately adjacent to the shoreline. I have never known a bullfrog to attempt an escape onto the shoreline. When escaping perceived danger, bullfrogs go directly to the bottom, not moving too far laterally. On the bottom, they shut their eyes and simply do not move . With their eyes closed and feeling secure as they rely on surrounding vegetation, they are oblivious to anything around them..
This is the same escape mechanism the American Alligator uses in the Everglades. Both animals feel completely secure within their escape cover. And as with the gator in shallow Everglades waters, once submerged, and with its eyes shut, the bullfrog has no idea if it is being watched from above.
If a GBH sees a bullfrog as or before it is submerging, the frog has no chance for survival.
GBH's are highly effective hunters. Their long toes keep them buoyant on the soft and deep detritus. Their long legs and long body and neck, give their eyes a very lofty perspective of any fauna activity occurring in the shallows. And the GBH will spend most of its hunting-time standing absolutely still, with no head movement as it intensely scrutinizes the shallow vegetation for any movements. To any aquatic fauna that is looking upward, the GBH's plumage is cryptically colored against similarly colored foliage along the water's edge. Add to all of this that the shallow edges of a body of water are the most productive. The edge has the greatest species-diversity. And the GBH will kill and eat ANY living animal that it is capable of subduing and even some that it finds it cannot swallow. Among wading birds, the Great Blue Heron is the most assailing. There's an abundance of documentations of the GBH attacking and trying to swallow mammals that are just too large to swallow. I once knew a GBH that made its living in upland fields by spearing/swallowing Boreal Red-backed Voles.
Bullfrogs are solitary and territorial, each laying claim to a specific piece of shallow water, along the shoreline. And the shallows, along the pond edge, are the hunting grounds the GBH favors....overwhelmingly. Just a few GBH's have the potential to kill and eat ALL the American bullfrogs along a pond's edges.
Big bass cruise just outside the edge of the emergent , aquatic vegetation and they even push into and through that vegetation, toward the shore. The frogs have no chance out here. So the frogs must stay very tight to the shore and take their chances with the GBH.
I am virtually certain the bullfrog in this picture later fell prey to one of the GBH's that frequent this pond edge.