Big Night is a mass migration of thousands of salamanders, wood frogs, spring peepers, and other amphibians that make their annual spring commute to vernal pools and other wetlands to breed. Although it is called Big Night, it rarely occurs on just one evening. Before getting into details about this amazing event, I would like to explain what a vernal pool is since it is central to this phenomenon. Vernal pools, also called vernal ponds, spring ponds and ephemeral wetlands, are water bodies, that are variable in size, and usually only exist for a short time. The name comes from the Latin word, ‘Ver’, which means, ‘production of spring’. These temporary bodies of water are seen throughout the eastern part of our country and may exist between fall and summer. Most of the water that collects in them is from snow melt or rain accumulation. By mid to late summer, they usually dry up. Whatever name they go by, these water bodies are absolutely essential for the life cycle of many of our invertebrates, (animals without spines), and amphibians, which are cold blooded vertebrates (animals with spines), that exist both in water and on land. Vernal pools provide many services and are an important component of the forest community. Besides serving as the destination point for the mating and breeding of many species, the nutrients from the fallen leaves of the surrounding trees support a rich food web. As the leaves decompose in the water, they become food for many invertebrates, amphibians and reptiles, (vertebrate animals with dry, scaly skin). These nutrients are ingested and cycled through these species and at their death are returned to the forest. The one aquatic vertebrate that is always absent in a vernal pool is fish. Fish would eat the eggs that are laid in these water bodies. The wet-dry cycle of vernal pools prevents these water bodies from having permanent populations of fish. “Big Night”, as referred to by herpetologists, (a person who studies reptiles and amphibians), is quite easy to predict. It occurs on the first or second consecutive rainy night when the ground has thawed and the temperature at night consistently reaches between 45 to 50 degrees Fahrenheit. In Ipswich, Massachusetts, where I live, that happens around March 17th or soon after. In my local on Big Night, hundreds and sometimes thousands of mole salamanders, (including the spotted salamander, the blue spotted salamander, the Jefferson salamander and the marbled salamander), the wood frog, and the spring peeper, emerge from their winter protection under leaves, under fallen logs or from tunnels in the soil and migrate en masse. Some of these winter habitats are as far away as a half-mile. No matter where these species are coming from their destination is to return to the exact pool of their birth. These are obligate species, (Their life cycles have evolved, adapted and 100% depend to the temporary conditions of the vernal pool). Their physical appearances and behaviors have also evolved with the wet-dry cycle of these water bodies. Once at their destination, they will spend a few days or weeks courting mates through song and often elaborate dances. In some communities including my own, this much loved and anticipated migration, sends teams of volunteers, including children from schools, to assist the frogs and salamanders safely across busy roads at night so to avoid becoming road kill. Some towns will even close specific roads to traffic on these nights. SPRING PEEPERS - I am going to focus on just two of the many main characters of Big Night, the spring peeper and the spotted salamander. The spring peeper is one of the first woodland frogs to dig itself out of its winter subterranean home. Every year I anticipate their sounds as a most welcomed harbinger of spring. Their shrill peeps, repeated roughly every second, are a love song that not only catches my attention but that of potential mates. As hundreds migrate to their water body destinations, a deafening chorus of shrill peeps rises in unison from the edges of water bodies. Spring is officially heralded in. As often as I have approached these water bodies to catch the sights and action this raucous noise proclaims, I am disappointed. At the site, silence is my only reward. Literally not a “peep” will I hear. However, with a little diligence and lots of patience, if I look under leaves at the edge of the pond or look up a foot or two from the ground on the bark in the nearest trees and shrubs, I will be rewarded with the sight of this small, ¾” being. They have smooth skin in shades of tan, brown, green or gray with lines that form an X-shaped pattern on their backs. Their bellies are white to cream colored and between their eyes they have a dark line. Female peepers are more or less silent with the male peeper doing all the singing. A male peeper repeats his sharp mating call about 4,500 times a night during breeding season. Besides the high-pitched whistle call that the male uses to attract a mate, the peeper has other distinctive sounds that are made to warn other males away from his territory, defense sounds and sounds that tells another male frog that he has mistakenly grasped another male frog. After breeding season, which can be from March to June, peepers leave their ponds and return to the woods where they will spend most of the year. They spend the summer and fall living on the forest floor eating spiders, mites, ticks and a variety of insects. They in turn are food for snakes, salamanders, large carnivorous insects, raptors and other birds. As winter approaches, they dig down into the soil below the frost line or dig under a log or find refuge in holes or loose bark in trees to hibernate. The cycle will begin again as they leave their winter shelter in the spring to make their annual migration back to the vernal pool or body of water where they were born to mate and lay eggs. The only requirement they have is that the body of water has at least three months’ worth of water. The female usually releases 800 to 1,000 eggs one by one on vegetation. The male while clasping the female in a hug called amplexus, releases his sperm as the female is releasing her eggs. In only a few days the eggs hatch and tiny tadpoles emerge. Within three months, if they are not eaten by aquatic invertebrates and salamander larvae, these tiny, legless, plant eating-tadpoles will transform into four-legged, insect-eating frogs. They will then leave the pond of their birth and migrate close by usually no more than 600 feet to a quarter of a mile. And the cycle continues. SPOTTED SALAMANDER - Not all mating rituals involve loud proclamations. Mating of some species, like the spotted salamander, take place under darkness and total silence. Their quiet annual mass migration to their ancestral vernal pool, although a most wonderous event, escapes the notice of most humans. Spotted salamander are 6- 9” long with shiny black skin and bright yellow spots. They are the largest members of the “mole” salamander family. Mole salamanders are so named because of their subterranean existence in shrew, mole or mouse tunnels. Normally, the only time they leave their below ground home is in the spring when they awaken from hibernation and migrate to the same pool where they were born so they can perform the mating ritual and breed. Often this pool is only several hundred yards away from where they hibernate. Although this mating process can extend over a two-week period, the majority of salamander will migrate on the first optimal night. With a little luck, any given salamander will live about 20 years and thus will make this trek 20 times in its life.
Whereas the spring peeper can mate in many types of water bodies including vernal pools, the spotted salamander will only migrate and mate in a vernal pool and it must be the same one of its birth. These vernal pools are essential to the continuation of several species of amphibians including the spotted salamander! It is vital that they be free of predators, especially fish, so that the eggs and then their larvae, have a fighting chance of survival. The salamander’s entire life cycle evolves around the brief viability of such temporary watering holes and breeding, egg laying, and larval development must occur within just a few months before the pool dries up. Salamander mating starts with the males often arriving at the vernal pool a few hours before the females. In the water, groups of males, from 12-100 salamanders, (called congresses), form slithering masses. Every so often a single male will leave the group and mate with a nearby female. The pair perform a courtship dance in which they circle each other on the bottom of the pool while placing their head under each other’s tail. The male will climb on the females back and repeatedly rub his chin against hers. If lucky, he convinces the female to swim to the spot where earlier he had deposited a sperm packet on the bottom of the pool. If he is successful, the female will pick up the sperm packet with her vent, (cloaca), allowing her eggs to be fertilized internally. The female will then lay her eggs, which are in a gelatinous envelope of about 2” across, on grass stems or branches at the bottom of the pool. Each egg is enclosed in a sphere of jelly about the size of a marble. The entire cluster of eggs is further enclosed in one big gelatinous envelope. Over time the egg mass doubles in size. It is often covered with algae turning the egg masses green. Algae provides a certain type of protein for the eggs turning them white and also offering some camouflage protection. The eggs will hatch in about a month and gilled larvae emerge. At this stage of their development salamanders are called efts. Efts are voracious predators and eat midges, mayfly nymphs, fairy shrimp and caddisfly larvae. Efts in return are eaten by snakes, birds and larger amphibians. One to four months later, the efts metamorphize, (change form), into juvenile spotted salamander. They are equipped with lungs that allow them to breath air and leave the pool and begin their largely subterranean life. These juveniles wait for rain to make this migration landward just as they will wait for rain to migrate back to the vernal pool to mate in the spring of next year. Spotted salamander continue to grow throughout their lives. Their diet consists mainly of earthworms, snails, slugs and spiders. They in turn are eaten by snakes and birds Concluding thought: Vernal pools and wetlands are specific and unique ecosystems that support a web of life consisting of certain plants, insects, birds and animals. All these species are bound to each other in an intricate food web. These environments provide habitat, food, shelter and opportunities for the next generation to be born and nurtured. Without these environments, the life forms that live within them and are dependent on them, will disappear. All ecosystems on our planet are important and essential, whether they are as large as a forest or as small as a vernal pool. Further resources on vernal pools, spring peepers and salamanders: Vernal Pool Association www.vernalpool.org Call your town’s/city’s conservation commission to find where your closest vernal pool is. Read: “A Field Guide to The Animals of Vernal Pools” by Leo Kenney and Matthew Burne “Vernal Pools: Natural History and Conservation” by Elizabeth A. Colburn
0 Comments
Leave a Reply. |
AuthorConsultant, designer and educator transforming commercial and residential landscapes sustainably Archives
March 2023
Categories |