How Herps survive during winter

Presentation by Dominic Pesavento

Questions I hope to answer

• What is a herp?• What problems face

herps trying to survive in winter?

• How do certain kinds of herps survive?

• Where do they go?

What is a Herp?• Herp, herptile and herpetofauna

are all terms referring to poikilotherms (ectothermic or “cold-blooded” animals) such as frogs, toads, salamanders, turtles, snakes, crocodilians and lizards, as well as the tuatara. This group does not contain fish, however. It also excludes invertebrate poikilotherms, such as insects, but that goes without saying.

Problems facing herps in Winter• Ectothermic (cold-blooded) animals, also known as Poikilotherms,

like fish, frogs, snakes and turtles have no way to keep warm during the winter. Snakes and many other reptiles find shelter in holes or burrows, and spend the winter inactive, or dormant. This is similar to hibernation.

• Reptiles and Amphibians mostly have two choices in Winter; hibernate or die. However, as will be discussed a little later, some herps have adapted ways of resisting freezing.

Herp Hibernation• Reptiles that hibernate in winter do so by burrowing into the ground or slipping into

a crack between two rocks. They stay there until the weather warms up. Before hibernating, a reptile eats a lot of food, which forms a layer of fat in its body. The fat serves as food during hibernation.

• Reptiles and amphibians will also seek shelter underground, in old logs, under trees, and in the mud of ponds and lakes. In ponds and lakes, frogs, turtles and many fish hide under rocks, logs or fallen leaves. They may even bury themselves in the mud. They become dormant. Cold water holds more oxygen than warm water, and the frogs, salamanders, and turtles can breath by absorbing it through their skin.

Snakes• Snakes will occasionally congregate in mixed species groups.

Copperheads, rattlesnakes, and Black racers have often times been found sharing rock dens in winter.

• In less frequent cases, countless thousands of a single species, such as the red-sided garter snake, will congregate in deep caverns (such as those found in southern Manitoba’s limestone country).

Turtle hibernation• As stated previously, turtles will often move to

lake and pond bottoms and hibernate in the soil. Terrestrial turtles, such as the box turtle, prefer a less amphibious lifestyle and so must hibernate elsewhere.

• Most box turtles live in geographic areas that require them to hibernate for three to five months of the year. Hibernation allows the box turtle to live until better times return in the spring. Hibernation is not a time of cozy sleep, but a dangerous time when bodily functions are barely keeping the box turtle alive. The heart rate slows, digestion stops and the turtle cannot voluntarily move or even open its eyes. Many unprepared turtles die during this period.

• In the early fall, box turtles start their search for a safe place to spend the winter such as in the south face of a hill that is easy to dig into and above water level, or under the sheltering roots of a large tree which will be blanketed with fallen leaves by winter. A deep abandoned gopher hole also works.

Land Hibernating Frogs• While some frogs hibernate in lakes

and ponds, toads and some frogs hibernate underground. They burrow for themselves in the dirt and sleep there until spring.

• Some land hibernating frogs overwinter beneath a scant layer of leaf litter, which provides less safety from the cold than the pond bottom

• Here their fate is certain; their water permeable skin virtually precludes any possibility of avoiding inoculative freezing from ice in their surroundings.

Freeze Tolerance in Frogs

• Having no way to escape the cold or generate their own body heat, they must find other ways of overwintering. Thus, Four species of frog- the spring peeper, chorus frog, gray tree frog, and the wood frog- have been identified as being “freeze tolerant”.

• Freezing in frogs is normally initiated at about -2 degrees to -3 degrees. Perhaps, because of this, they do not produce “artificial” ice nucleators, as seen in freeze tolerant insects.

Freeze Tolerance in Frogs (cont.)• The most common cryoprotectant in frogs seems to be glucose,

rather than the polyhydric alcohols (polyols) found commonly in insects. The effectiveness of glucose in freeze protection of frogs is apparently not solely related to the presence of other solutes, for its concentration is not high enough. Instead, it is likely related to some additional function, such as membrane protection

• So far, only the grey tree frog has been found to produce glycerol (though other cryoprotectants may yet be discovered).

• Perhaps the most unusual aspect of freeze tolerance in frogs is that it is not at all anticipatory. In frogs, glucose levels show no increase until body temperature drops below the supercooling point and ice actually starts to form on the frog. Suddenly the, glycogen from the liver is rapidly converted to glucose and dumped into the bloodstream at an incredible rate until the frog is severely diabetic.

Freeze Tolerance in Frogs (cont.)• Now the frog’s body is faced with

the dilemma of timely delivery of glucose (or glycerol in the grey tree frog) to body tissues while freezing progresses. This requires effective cardiovascular functions under exceptional conditions. Within one minute of ice nucleation, heartbeat has been seen to double.

• For the frog that successfully overwinters on land, life jumps back to normal as soon as the temperature picks up (that pun was intended). Within an hour after thawing, the frog’s heartbeat resumes and returns to normal 6 hours later, at a temperature of only 5 degrees Celsius. Thus, land-hibernating frogs can slip in and out of the frozen state quickly.

Salamanders• Salamanders will often hibernate in

pond bottoms (where they acquire oxygen through their skin, just like frogs and turtles), under leaf litter, and in logs.

• However, a salamander that has acclimatized to a temperature of 15 degrees Celsius might show a metabolic response to rapid temperature changes.

• In this case, its metabolic rate decreases considerably when exposed to colder waters. However, if held at the lower temperature for a period of time, it becomes “upward adjusted”, meaning its metabolism increases gradually. The salamander soon metabolizes at the same rate it did at 15 degrees. This has been observed in red-spotted newts.

Conclusion• In closing, reptiles aren’t exactly suited for the snow. However, they

have adapted ways that allow them to survive until spring.• Some gather together in large single species groups deep within

caves, others migrate to the bottoms of ponds and lakes to hibernate, and some can even survive frozen in a cryogenic state until spring, no worse for wear.

• Herps truly are interesting creatures.