Five months under ice: biologging reveals behaviour patterns of overwintering freshwater turtles

Abstract

Winter in temperate regions is characteristically the coldest period of the year. Species in these regions adapt to freezing temperatures with physiological or behavioural mechanisms to mitigate the threats of cold exposure. For aquatic species, taking refuge under the ice minimizes the risk of experiencing freeze injury. The Northern map turtle (Graptemys geographica; LeSueur 1817) is one species which overwinters under the ice of lakes and rivers. Here, we observed the behaviour of free-ranging map turtles at a known overwintering site throughout an entire winter using biologgers equipped with tri-axial acceleration, temperature, and depth sensors. We observed that map turtles maintain localized locomotor activity at the overwintering site continuously during the winter. The extent and patterns of locomotor activity and habitat use varied between adult females, adult males, and juvenile females. Adult females were observed at the shallowest depths, coldest temperatures and moved the least whereas juvenile females were observed at the deepest depths, warmest temperatures and moved the most. All groups remained at temperatures near freezing (0.98 –1.39C) and at average depths ranging from 1.34 – 1.7m. These behavioural patterns are consistent with a strategy to survive the winter while remaining aerobic and likely reflect differences in physiological demands.

Overwintering under ice: A novel observation for an Australian freshwater turtle

“…While the winter activities of North American freshwater turtles are well documented (Robichaud et al., 2023 ), observations of Australian chelids have largely been limited to areas where winters are relatively mild (Seebacher et al., 2004 , Van Dyke et al., 2023 ) or in laboratory settings (Chessman, 2019 ). Freshwater turtles are widespread along coastal Australia, with 25 native freshwater species across the continent (Van Dyke et al., 2018 ).…”

Overwintering Behavior and Predation in Common Musk Turtles (Sternotherus odoratus)

“…Although overwintering turtles reduce their activity substantially, several species remain somewhat active in winter (Taylor and Nol 1989; Greaves and Liztgus 2007; Plummer and O'Neal 2019; Robichaud et al 2023). Studying overwintering activity can help us to understand how turtles behave to cope with the challenges associated with overwintering, such as gas exchange (e.g., Plummer and O'Neal 2019; Robichaud et al 2023). Understanding the behavior and ecology of turtles in winter can thus offer important insights on the distribution and abundance of turtles at northern latitudes.…”

“…The average water temperature recorded 30 cm above the substrate at turtle locations was 0.9°C. Other temperate turtles have also been reported to overwinter in water around 1°C (Greaves and Litzgus 2007; Rollinson et al 2008; Edge et al 2009; Robichaud et al 2023). Selecting cold temperature during the winter may be a means to behaviorally reduce metabolism and thus the demand for oxygen at a time when dissolved oxygen may become limited.…”

“…Some radiotagged turtles travelled considerable distances under the ice indicating that, at least in our study population, some individuals are active in winter. Several species of freshwater turtles have been reported to be somewhat active in winter (Taylor and Nol 1989; Greaves and Liztgus 2007; Plummer and O'Neal 2019; Robichaud et al 2023), but few studies have measured the distance travelled by turtles under the ice. Greaves and Litzgus (2007) reported that wood turtles ( Glyptemys insculpta ) travelled up to 10 m between relocations (7–12 d apart) and Edge et al (2009) reported that Blanding turtles ( Emydoidea blandingii ) moved < 1 m under the ice between relocations (interval unspecified).…”

“…Both species are considered anoxia intolerant in winter (Ultsch 2006) and may thus be expected to seek similar overwintering habitats and behaviors. However, in Opinicon Lake, hundreds of northern map turtles overwinter gathered together in a shallow and rocky area with limited aquatic vegetation (Feng et al 2020; Robichaud et al 2023). The propensity of northern map turtles to form large overwintering aggregations may indicate that overwintering habitats with sufficient dissolved oxygen are limited (Graham and Graham 1992).…”