The ecology of overwintering among turtles: where turtles overwinter and its consequences

Abstract

Turtles are a small taxon that has nevertheless attracted much attention from biologists for centuries. However, a major portion of their life cycle has received relatively little attention until recently - namely what turtles are doing, and how they are doing it, during the winter. In the northern parts of their ranges in North America, turtles may spend more than half of their lives in an overwintering state. In this review, I emphasise the ecological aspects of overwintering among turtles, and consider how overwintering stresses affect the physiology, behaviour, distributions, and life histories of various species. Sea turtles are the only group of turtles that migrate extensively, and can therefore avoid northern winters. Nevertheless, each year a number of turtles, largely juveniles, are killed when trapped by cold fronts before they move to safer waters. Evidently this risk is an acceptable trade-off for the benefits to a population of inhabiting northern developmental habitats during the summer. Terrestrial turtles pass the winter underground, either in burrows that they excavate or that are preformed. These refugia must provide protection against desiccation and lethal freezing levels. Some burrows are extensive (tortoise genus Gopherus), while others are shallow, or the turtles may simply dig into the ground to a safe depth (turtle genus Terrapene). In the latter genus, freeze tolerance may play an adaptive role. Most non-marine aquatic turtles overwinter underwater, although Clemmys (Actinemys) marmorata routinely overwinters on land when it occurs in riverine habitats, Kinosternon subrubrum often overwinters on land, and several others may overwinter terrestrially on occasion, especially in more southern climates. For northern species that overwinter underwater, there are two physiological groupings, those that are anoxia-tolerant and those that are relatively anoxia-intolerant. All species fare well physiologically in water with a high partial pressure of oxygen (PO2). A lack of anoxia tolerance limits the types of habitats that a freshwater turtle may live in, since unlike sea turtles, they cannot travel long distances to hibernate. Hatchlings of some species of turtles spend their first winter in or below the nest cavity, while hatchlings of other species in the same area, including northern areas, emerge in the autumn and presumably hibernate underwater. All hatchlings are relatively anoxia-intolerant, and there are no studies to date of where hatchling turtles that do not overwinter in or below the nest cavity spend their first winter. Equally little is known of the ontogeny of anoxia tolerance, other than that adults of all species are more anoxia-tolerant than their hatchlings, probably because of their better ossified shells, which provide adults with more buffer reserves and a larger site in which to sequester lactate. The northern limits of turtles are most likely determined by reproductive limitations (time for egg-laying, incubation, and hatching) than by the rigors of hibernation. Mortalit...

A unique life history among tetrapods: An annual chameleon living mostly as an egg

“…1). Some other reptile species may hatch before emergence and overwinter inside the nest as hatchlings (32). However, in chameleons, this scenario appears unlikely because the group is mostly characterized by long incubation periods; delayed nest emergence, after hatching, has never been observed for any captive chameleon (26,28).…”

Post-Emergence Movements and Overwintering of Snapping Turtle, <em>Chelydra serpentina</em>, Hatchlings in New York and New Hampshire

“…V. Lamoureaux (personal communication), while studying the use of seeps as hibernacula for Green Frogs (Rana clamitans) in New York (Lamoureux and Madison 1999), found one adult and three juvenile (9.5 -11 cm) Snapping Turtles leaving a seep area in late April, where they apparently overwintered, and moving toward a nearby pond. Dunson (1986) radiotracked four snapping turtles in a tidal marsh area in Virginia, and they all moved to seep/spring areas on higher ground, which remained unfrozen throughout the winter, suggesting that the use of seeps as hibernacula may not be limited to immature turtles, although almost all reports of hibernacula of adult Snapping Turtles are of those covered by standing or flowing water (Ultsch 2006).…”

“…The typical approach of a study of overwintering behavior, a number of which have been done with adult turtles (reviewed by Ultsch 2006), has been the use of radio telemetry, permitting tracking of the turtles throughout the hibernation period, including entrance and exit. Recently, transmitters small enough to attach to hatchlings have become available, which allows tracking of the animals from the nest to their wintering grounds, although battery life is not yet long enough to track the turtles until the following spring.…”

Over-wintering Characteristics of West-Central Wisconsin Blanding's Turtles, <em>Emydoidea blandingii</em>

“…Two physiological over-wintering strategies are presently recognized among northern freshwater turtles: those that are anoxia-intolerant (death < 50 days), and those that are anoxia-tolerant (death > 100 days) (Ultsch 2006, Ultsch andReese 2008). Even within a species, tolerance among individuals varies by locality.…”

“…Reese et al (2004) demonstrated that Painted Turtles displayed varying tolerance to anoxia depending on whether individuals were from the northern or southern edge of their continental range. Ultsch (2006) believed that Blanding's Turtles are anoxia-tolerant because they share similar over-wintering habitats with Snapping and Painted Turtles. The species' winter metabolic rate (oxygen demand) is reported to be between the values of Painted and Snapping Turtles (Graham and Butler 1993).…”