American Toad Succumbs To Winter Challenges
Last fall most American Toads burrowed below the frost line, digging backwards one to two feet into the ground before beginning their winter hibernation. This spring, as soon as the temperature is consistently above 40°F., they will emerge.
Unfortunately, it seems that the pictured toad emerged too early during one of our warm spells this winter (of which there were many). One can’t know for sure, but it looks as though this is what happened, and without an adequate food supply it died of starvation or froze when the temperature dropped back down. To the left of the desiccated toad is some scat which looks very much like American Toad scat to me.
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American Toads Preparing For Winter
In the Northeast, sometime in September or October you realize that you’re no longer seeing American Toads. This is because they are taking steps that allow them to survive over the winter. These steps consist of either finding another animal’s burrow or digging their own (up to 20 inches or so deep) in order to hibernate below the frost line.
As the photograph illustrates, toads dig their tunnels facing forward, using their hind legs to do the digging. Special hardened knobs on their hind feet assist them in this endeavor. As they dig deeper, the tunnel in front of them collapses. When deep enough to hopefully avoid being frozen, they stop digging and hibernate until the soil begins to warm. Come April or May, American Toads dig their way up to the surface of the ground and head for breeding ponds. (Photo by Ashley Wolff)
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Big Night Approaching
Every spring there comes a day when the temperature approaches or exceeds 45 degrees, and a gentle spring rain occurs and extends into the night.* These conditions signal the impending nocturnal migration of many amphibians to their breeding pools. Spotted Salamanders, Jefferson/Blue-spotted Salamanders, Wood Frogs, Spring Peepers and an occasional American toad rise from their state of hibernation to crawl out of the dirt and make their way to wetlands (often vernal pools) where they will breed and lay their eggs. So many migrate en masse that the first night that this migration takes place has been dubbed “Big Night.”
It goes without saying that in many cases, roads have to be crossed when going from hibernaculum to breeding pool. This poses a major threat to the frogs and salamanders that are on the move, and roads often become slick with their carcasses due to unwitting automobile drivers. If you are out driving on the first warm, wet evening this spring, drive slowly while keeping an eye out for lumps in the road, and if you see them and have a flashlight or head lamp handy (to find the frogs and salamanders, as well as to announce your presence in the road to other drivers), stop and lend them a hand (usually there are concentrated areas where crossings occur). (Perhaps a group of well-marked volunteers could gather to monitor and assist migrating amphibians at major road-crossing locations in your town.) It should be obvious which direction the frogs and salamanders are all headed in, and they can be placed well off that side of the road. (Photo: left to right, Wood Frog, Spring Peeper, Spotted Salamander)
*With one to two feet of snow on the ground and vernal pools still frozen over in many parts of northern New England, this event will most likely not occur with the impending warm, rainy weather, but will happen in the next few weeks.
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American Toad Parotoid Glands
One of the adaptations that allowed the first amphibians to spend time on land was their skin, as it helped prevent them from drying out. It also served as an effective defense mechanism.
The skin of the American Toad contains multiple glands, both mucous and granular. Mucous glands are scattered all over a toad’s body and secrete a transparent mucus secretion that acts as a lubricant in water and also helps keep their skin moist on land. Granular glands contain a toxin that deters many predators, and is a toad’s main way of defending itself. (In addition, the toxin also protects a toad’s skin from microorganisms as well as helps repair wounds.)
Sometimes clusters of granular glands form a pad, or “macrogland.” American Toads have two such pads, or s parotoid glands, which are located behind their eyes. When threatened, a toad adopts a defensive stance, inflating its body and standing with its hindquarters raised and its head lowered, a position which makes its parotoid glands the first thing that an attacking predator encounters. The secretion from these glands generally induces very serious inflammations of a predator’s eyes or digestive tract, as well as vomiting. Some predators are immune to this toxin, while others, like the American Crow, have figured out a way to prey on toads without consuming any poison — it punctures the toad’s skin with its beak and then pecks out the toad’s liver without ingesting any toxin.
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Amphibians Migrating
Vermonters were witness to a record-breaking (early) amphibian migration in the Champlain Valley last week on March 1st, when night temperatures were in the low 50’s. Not only did it occur a week earlier than any other previous major migration, but records show that migration for the earliest amphibians in Vermont is now approximately two to three weeks earlier than it has been during the last decade. (as reported by Jim Andrews, www.VtHerpAtlas.org).
Spotted Salamanders, Four-toed Salamanders, Eastern Red-backed Salamanders, Blue-spotted Salamanders, Jefferson Salamanders, Spring Peepers, Wood Frogs and even an American Toad were on the move. According to Andrews, “this is a concern if the weather turns really cold and the ground and ponds refreeze. If that happens, many of the early migrants (that are not freeze tolerant) could freeze and die. If the weather stays relatively mild, with only short cold snaps, they should be fine.” Weather since these sightings has been unseasonably cold, and one can only hope they survived. (Photo: Spotted Salamander, Ambystoma maculatum)
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American Toad Eggs Hatching
American Toads lay their eggs in double strings (one from each ovary) which can be three or more feet long and may contain 4,000 – 8,000 eggs. It doesn’t take long for toad eggs to hatch – just one week, or two at the most. The gelatinous strings begin to disintegrate, and tiny, dark tadpoles are released into the water. If nothing untoward occurs, the tadpoles will attach themselves to underwater vegetation or their egg mass for a few days, and hang vertically with their heads up.
Many aquatic predators, including Eastern Newts, consume both American Toad eggs and tadpoles. The pictured newt waited patiently nearby until tadpoles wiggled their way out of the gelatinous egg string and then immediately snatched and ate them. In another week toad tadpoles will be crowding the shallow shoreline water, and in two more weeks they’ll be metamorphosing into little toadlets.
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Spring Peepers Peeping
The sound of a peeping Spring Peeper in December (yes, this occurred in Vermont this week) conveys to one and all that climate change is not a figment of our imagination. Amphibians are extremely sensitive to small changes in temperature and moisture due to their permeable skin and shell-less eggs. Certain species, including Spring Peepers, Grey Tree Frogs, Wood Frogs, American Bullfrogs and American Toads, are emerging and mating earlier in the year than they did historically. Causal relationships have been found between irregular climate conditions (drought, increasing frequency of dry periods and severe frosts) and decreasing (extinction in some cases) of certain amphibian species.
Behaviorally and physically, warming temperatures are having an impact on amphibians. A recent laboratory study investigated changes in amphibian metamorphosis time due to pond desiccation and whether amphibian immune systems become compromised as a result of these changes. They found that amphibian immune responses became increasingly weaker and white blood cell counts were increasingly lower with higher desiccation. As a result of climate effects, immune systems are weakened, making it more difficult for amphibians to fight off diseases.
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September Snub-Noses
Frogs and toads that hatched from eggs laid this past spring are now two to four months old, and are growing rapidly. Like snakes, frogs and toads shed their skin as they grow — unlike snakes, they eat their skin. Periodically toads and frogs stretch their bodies and then pull their loosened skin off in one piece, much like we pull off a sweater. Using their feet, they then stuff their skin under their tongue and swallow it. When frogs and toads are young and growing fast, they usually shed their skin more often than when they are older and their growth slows down. Not only is their skin a valuable source of nutrients and protein, but if it’s eaten, there is no sign left behind for predators to find.
Most young toads and frogs, with the exception of the Gray Treefrog, look like miniature adults. (Gray Treefrogs are emerald green in their youth, unlike the mottled gray/green adults they will become.) There is one characteristic at this stage that they don’t share with their elders, however, and that is their snub noses. If you’re wondering if the frog or toad you saw is a small adult or a youngster, take a closer look at its nose! If it’s unusually short and blunt, there’s a bit of growing left to do.
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Carrion Beetles Feeding
When an organism dies, such as the pictured American Toad, a series of decomposers appear and break it down. Some of the first insects to arrive at the scene are blowflies, and they lose no time in laying eggs which rapidly hatch into larvae, or maggots. A bit later, carrion beetles move in. Both of these insects live in dead carcasses, where they eat raw flesh and fungi. There is great competition, believe it or not, for rotting bodies, and carrion beetles such as the pictured American Carrion Beetle (Necrophila americana) have managed to find a way to eliminate some of it. They carry tiny mites on their backs which travel from carcass to carcass with the beetles, devouring the eggs of maggots as well as the smallest maggots themselves. In addition, carrion beetles secrete a strong offensive odor that irritates other insects and predators, a second effective way to reduce the number of insects competing for a corpse.
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