Vernal ponds open, many critters respond
It was just a couple of weeks ago as I walked around on a mild WinSprin (winter-spring) day and I went to see how the local vernal ponds were doing. All were covered with ice, some even with a layer of snow over the frozen surface. They appeared a bit low and smaller than I like to see, but probably had ample water for their next phase. March turned into April and with about 13 hours of daylight each day and temperatures that regularly reached into the 40s and 50s early in the month, the ice lost its grip. The ponds were thawing.
Since they appear as small bodies of water we call them ponds and in the spring, they are often referred to as vernal ponds (vernal meaning spring). They vary greatly. Some have water permanently for years, but most hold water for only the months after the coming of spring and are usually devoid of water by midsummer. This location on those warm days may give the appearance that they never were here.
Despite these conditions there is plenty of life in these ponds, which are frequently temporary. The inhabitants of these sites need to adapt to such a changing life. Whatever the length of the pond's aquatic phase, nearly all are small and shallow and often do not even appear on the regional maps.
The vernal ponds that I visit are mostly in woods but they may appear in fields, yards and at the edges of other bodies of water such as swamps and lakes. Because of an ephemeral existence, they may be seen as unimportant and therefore some have been plowed under, paved over or just not noticed. But these small changing wetlands are the home to a plethora of critters that live all or part of their lives here.
Perhaps the best known of these sometime residents are the newly awakening frogs. My walks to the vernal ponds in mid-April are associated with the songs of a trio of early-rising frogs: wood frogs, chorus frogs and spring peepers. The gray to reddish-brown wood frogs, at 3 inches, are the largest. They make clucking sounds while the 1-inch chorus frogs produce a creaking song (often compared to the noise made by running your thumb over the teeth of a comb) and the equally tiny spring peeper gives its high pitches to the group.
After a winter under leaves and snow on land, they quickly come to the vernal ponds where the males call to get the attention of females and together they form egg masses, usually in gelatinous covering. Since the ponds will not be here in a couple of months, the hatching tadpoles need to develop rapidly and leave the water as territorial frogs in the next several weeks. Salamanders, here, too, quietly mate and lay eggs.
There is far more in the ponds that these amphibians. Each time I return to these vernal waters I find more. Many kinds of insects, both adults and immature, use these ephemeral wetlands as their home. The adults of water boatmen, water striders, whirligig and diving beetles swim here. They wintered either in deeper-water sites or hibernating on land. In a similar way is the life of the fishing spider that I see running over the surface. Other insects hatch from eggs in the water, usually on the bottom, and now move about. These aquatic larvae include damselflies, dragonflies, caddisflies, midges and the ever-present mosquitoes. In usual insect fashion, they survive tough conditions and go through their growing phases to reach adulthood, often within a week or month.
Being temporary, most vernal ponds do not host a population of fishes and therefore these youthful frogs and insects are able to grow up without fish predators. But though the anurans and insects are abundant and I find more every time that I look, there are other residents that are marvels of adaptation.
The crustaceans known as water fleas, only about the size of a dot, swim here. This is no surprise and it seems like nearly any amount of water has some. But there is a large crustacean present, too, the fairy shrimp. Being an inch long, orange and swimming with an undulating motion, they are easy to find. Mysteriously, they appear only in spring ponds. Hatching from eggs that were dried in the pond bottom, they emerge to swim, feed and mate in spring. Not seen here at other times, I always locate them in this time of year. Equally surprising are the snails and tiny clams that live here now. Both are able to cope with the absence of water in the warm and cold times within this pond site.
I'm not the only one to visit these little ponds. I often see wetland birds such dabbling ducks, sora rails and sandpipers. But swamp sparrows, warblers and thrushes show up to feed, too. Shrews, mice and raccoons search here as well.
In April, the sunlight penetrates the woods to these aquatic sites, but soon they will be in shade. Warming days will evaporate the water and by midsummer, the vernal ponds of April will be just a memory. But now, with the plentiful and varied life adapted to such changing conditions, I expect they will do fine in later weeks.