Western painted turtle (Chrysemys picta bellii) COSEWIC assessment and status report 2012: chapter 8
Courtship and mating in Painted Turtles begins almost as soon as the turtles become active in spring and continues throughout the active season (Ernst et al. 1994). There is a peak in successful copulation in the late summer and early fall (Gist et al. 1990). Male painted turtles actively court females; a male will follow a female and when facing, vibrate his elongated foreclaws on either side of the female’s face. He may repeat this courtship behaviour numerous times, often swimming away between bouts, enticing the female to follow. Responsive females may reciprocate by vibrating their claws near the forelimbs of the males. Courtship lasts up to 15 minutes, after which the female sinks to the bottom of the pond followed by the male. Once submerged, the male mounts the female from behind and moves his tail under her to copulate (Gregory and Campbell 1987). Male and female C. picta generally avoid each other except when courting and mating (Munoz 2004).
The Painted Turtle mating system is promiscuous and, as such, a small proportion of clutches have multiple paternity (13% in Illinois; Pearce and Avise 2001). Females also have the ability to store viable sperm for two to three consecutive years; however, the majority of C. p. bellii females mate prior to each nesting period (Pearce and Avise 2001). There is a small, but statistically significant, higher rate of hatching success in clutches with multiple paternity (Pearce and Avise 2001).
In Canada, Painted Turtles begin nesting in June (late May where the climate is mildest) (Ernst et al. 1994; Schwarzkopf and Brooks 1987). Females usually dig their flask-shaped nests within 200 m of water in open soil (Ernst et al. 1994) but may respond to absence of predators and travel further from water if risk of depredation (both nest and adult) is low (Spencer 2002; Spencer and Thompson 2003). At the microhabitat scale, females select nest sites that optimize incubation conditions and suitability of habitat for neonates (Schwarzkopf and Brooks 1997; Kolbe and Janzen 2001). For example, in New Mexico where risk of dessication and overheating is high, Painted Turtles nest under canopy cover and near standing water (Morjan 2003a) while in northern populations, where length of growing season may be a limiting factor, Painted Turtles usually nest on open south-facing slopes (Schwarzkopf and Brooks 1997; Weisrock and Janzen 1999).
Oviposition in northern populations of C. picta generally occurs in late afternoon and evening, when temperatures are warmest. Females void cloacal water on their chosen nest sites and excavate the 10-cm deep, flask-shaped nest using only their hind feet. Following oviposition, the female fills in the nest cavity with the excavated soil and packs it down with intricate dance steps of the hind limbs (R. Brooks pers. comm. 2005). The entire nesting process generally takes one hour. Females do not always complete nesting in the first chosen location (20% of attempts completed at Revelstoke Airport, B.C.; Maltby 2000). This low success rate is due to poor substrate conditions and interference by predators or other disturbances. Painted Turtles commonly lay a single clutch of eggs within a single active season in Canada, but a significant proportion also lay a second clutch 1-2 weeks after the first (Gregory and Campbell 1987; St. Clair et al. 1994; Samson 2003). Clutch frequency is inversely related to latitude, with two or more clutches laid in a season in warmer parts of the species’ range (Iverson and Smith 1993; St. Clair et al. 1994). C. picta clutch size ranges from one to 23 eggs; the C. p. bellii subspecies lays the largest clutches (Ernst et al. 1994). Individual eggs are up to 35 x 22 mm in size and weigh up to 9 g when laid; they are elliptical, with a white, slightly pitted shell that calcifies during incubation (Ernst et al. 1994). Painted Turtles trade off reproductive potential of the female against growth potential of offspring because of the constraint imposed by the fixed size of the pelvic aperture in female turtles (Rowe 1994). Clutch size and reproductive frequency do not increase with age, but egg size and hatchling size do, concomitant with an increase in the size of the pelvic aperture (Lindeman 1991; Rowe 1994; Congdon et al. 2003; Samson 2003). Female Painted Turtles supplement their eggs with 50-60% more lipid than is required for hatching and emergence to enhance the potential survival of their offspring (Zug 1993). This excess helps to meet energetic needs prior to the hatchling encountering favourable feeding conditions (Zug 1993). The size of the energy reserve available to hatchlings is related to the thermal regime of the previous winter (Costanzo et al. 2004).
Incubation averages 76 days in natural and artificial nests (72-104 days in the Pacific Northwest; Nussbaum et al. 1983). Offspring sex is determined by temperatures experienced by the embryo during a critical period of incubation (temperature-dependent sex determination, TSD) (Ewert et al. 1994). Eggs incubated at higher temperatures (constant temperatures ≥29˚C) produce female hatchlings, whereas lower incubation temperatures (≤26˚C) produce male hatchlings (Schwarzkopf and Brooks 1985). At a pivotal temperature of 28˚C, an approximately equal number of males and females are produced, and between 26-28˚C both males and females are produced in varying ratios. Bobyn and Brooks (1994) reported that incubation temperatures below 25˚C reduce hatching success, post-hatching survival and hatchling growth rates in the Snapping Turtle (Chelydra serpentina), and that temperatures around 25-27˚C enhance hatchling performance. Temperatures above these values tended to correlate with increasingly reduced hatchling performance and survival as the temperature increased. In Painted Turtles, which have only one pivotal temperature, compared to two in the Snapping Turtle, it appears that the optimal temperatures for growth and survival of embryos and hatchlings are around 28-30˚C, which corresponds to temperatures which produce the larger sex, which is the female in this species.(Schwarzkopf and Brooks 1985, 1987). Freedberg et al. (2004) found that higher incubation temperatures were positively correlated to enhanced righting ability in two species of TSD turtle, including C. picta.
Survival of Hatchling Painted Turtles is related to winter nest temperatures (Packard et al. 1997). Following hatching in late summer and early fall, hatchling Painted Turtles usually remain within the shallow subterranean nest until the following spring (Gregory and Campbell 1987; St. John 2002). Thus, hatchlings must often cope with subzero temperatures during winter months (Packard and Packard 2003).
Adult painted turtles hibernate aquatically in ponds or streams, whereas hatchlings usually overwinter terrestrially within the natal nest chamber, approximately 10 cm or less below the ground surface (Ultsch 1989). The eggs hatch in the fall, but the hatchlings do not emerge from the nest chamber until the following spring, and so they may be exposed to temperatures as low as -10˚Cduring hibernation. In northern regions with sparse or transient snow cover, hibernating hatchlings may be exposed to temperatures below the freezing equilibrium temperature of their body fluids (-0.6˚C) for extended periods of time during hibernation (Costanzo et al. 2000). For example, Nagle et al. (2000) recorded a C. picta hatchling mortality rate of 45% during a cold, snowless winter in Michigan with soil temperatures of –7 to –9˚C, and a mortality rate of less than 3% in three consecutive mild winters with snow-insulated soils that remained above –2˚C.
The winter survival of hatchling Painted Turtles exposed to subzero temperatures may be promoted by both freeze-tolerance and supercooling. Because hatchlings apparently tolerate freezing only if body temperature remains above -4˚C(Storey et al. 1988; Churchill and Storey 1992; Costanzo et al. 1995), survival at temperatures lower than this is only possible if hatchlings remain supercooled (Packard et al. 1997). Although hatchling Painted Turtles can supercool extensively in the lab (to -15˚C; Costanzo et al. 1998; 2000), in nature supercooling may be constrained by environmental ice nuclei that seed the freezing of their body fluids. Freezing is inevitable in sandy soils (which have high water potential) with high water content, whereas supercooling is promoted in dry, organic soils (Costanzo et al. 1998). Interaction with ice nuclei in the winter microenvironment of the nest chamber (e.g., ice, sand crystals, bacteria) determines whether hatchlings remain supercooled or freeze (Costanzo et al. 1998). These interactions may ultimately account for variation in winter survival rates among populations.
There is no documented post-hatching care in this species (Zug 1993). Frazer et al. (1991) reported age specific juvenile annual survival rates of 0.21 to 0.51 in Michigan, with survival to adulthood being estimated at 0.9%. St. Clair (1989) suggested that the mortality rate is constant for all age groups (aside from hatchlings). However, recent long-term studies of C. p. marginata in central Ontario show that annual survival of juveniles gradually rises from about 0.7 at age 1 to adult rates of about 0.98 by age 4 (Samson 2003). Summer growth of young turtles is rapid, and they can attain a plastron length of 83 mm in three to five years depending mainly on food supply (Nussbaum et al. 1983). Growth rate begins to decrease as sexual maturity is approached, and adults have slow, indeterminate growth rates (Samson 2003).
In the more central parts of the range of Chrysemys picta bellii within the U.S.A., males usually take four years to mature whereas females normally take five years at southern latitudes and seven or eight years in colder climates (St. Clair et al. 1994; Cooley et al. 2003). In central Ontario, C. p. marginata males matured at 8-10 years and females at 12-15 years (Samson 2003). It is likely that these values are similar to those of Western Painted Turtles in much of the central and eastern parts of their range in Canada. However, both sexes can attain maturity within two years when environmental conditions are highly favourable for growth and development (Frazer et al. 1993; Lindeman 1996), usually in the warmer (southern or coastal) parts of their range (Gregory and Campbell 1987).
Frazer et al. (1991) recorded a maximum age of 34 years in a Michigan study, with annual male survivorship of 0.64 to 0.83 and annual female survivorship of 0.29 to 0.50. However, these studies likely underestimated survival because of low recapture frequencies. Long-term research in southeast Michigan (Congdon et al. 2003) and central Ontario (Samson 2003) on C. p. marginata indicate that adults have very high annual survivorship (>0.98), and that ages in excess of 50 years are often achieved.
As ectotherms, turtles need to bask to raise their body temperature to a level suitable for activity (the sun’s ultraviolet rays also help to eliminate skin parasites, and are essential for the synthesis of vitamin D3). Consequently, Western Painted Turtles spend their nights sleeping on the pond bottom or on partially submerged objects and become active during daylight hours. They bask for several hours at sunrise before feeding and may bask and forage again in the afternoon and evening. Basking time decreases with increasing ambient temperature (Lefevre and Brooks 1995). Females may bask more during the nesting season (Krawchuck and Brooks 1998). Juveniles appear to bask for shorter periods of time, possibly because their smaller body size allows them to heat faster and because they display greater predator avoidance behaviour (Lefevre and Brooks 1995). Basking substrates include mudbanks, rocks, logs, or other floating objects. There is no aggression shown during basking; individuals will even pile into stacks of several layers. It is unknown if there is social hierarchy in the wild, but a dominance hierarchy is quickly established in captivity: large turtles feed first and the least aggressive feed last (Ernst et al. 1994). Younger turtles primarily occupy the shallow portions of a pond and move to increased water depth with increasing size and age through to sexual maturity (Congdon et al. 1992). Shallow waters are generally warmer and more productive and can thus enhance foraging and growth rates.
During winter, juvenile and adult painted turtles become dormant on the muddy substrate of ponds or seek muskrat burrows or other suitable shelter (Cohen 1992). Western Painted Turtles hibernate in shallow water below the freezing limit, remaining in one location or small area throughout the winter (St. Clair and Gregory 1990). The length of hibernation and the onset of breeding are governed by water temperature. While dormant, their need for oxygen is greatly decreased (Ultsch et al. 2001), and they may absorb oxygen from the water through their skin, throat linings and thin-walled sacs in the cloaca ). It appears, however, that Painted Turtles are unable to maintain aerobic metabolism throughout an extended hibernation. Instead, they survive on anaerobic respiration, by using calcium and magnesium carbonates taken from their shell to buffer lactate accumulation in their tissues (Dinkelacker et al. 2005). Painted Turtles are the most tolerant turtle species to anoxia in Canada (Reese et al. 2004), and the Western Painted Turtle has a greater ability to tolerate and survive prolonged anoxia than does any other subspecies of this species (Ultsch et al. 1985), perhaps as an adaptation to its northern distribution and longer winters. Although a progressive lactate acidosis occurs through winter, levels are well below the maximum tolerable level for this species, even at northern latitudes (St. Clair and Gregory 1990).
Based on a study of Midland Painted Turtles in a small marsh system in southernMichigan, males and females occupy similar-sized home ranges and individuals usually favour one or two core areas (Rowe 2003). Rowe (2003) documented an average home range size of 1.8 ha in 1999 and 0.7 ha in 2000 in his study, and average daily travel distances of 39 m/day in 2000 and 102 m/day in 1999. Low annual precipitation in 2000 caused the marsh to be reduced in size and this decrease may account for the differences in distances moved. During summer, movement was not related to sex, daily water temperature, or weather conditions.
Female turtles use upland habitats during nesting. They have been known to move up to 150 m from the water (Gregory and Campbell 1987; St. John 2002). A recent movement study demonstrated that distance traveled is inversely proportional to availability of good nesting habitat near a pond (Baldwin et al. 2004). In an Algonquin Park population, almost all nests (>99%) were within 3 m of water, largely because that is the only area where suitable nesting sites occurred (Schwarzkopf and Brooks 1985; Samson 2003). However, even when other suitable nesting habitat is available further from water, most females prefer nesting close to water, perhaps because of the risks associated with nesting further from the water’s edge (R. Brooks pers. comm. 2005). Male turtles are more active in spring when they search for mates (Gibbons 1968).
Some turtles use different wintering and breeding ponds, and must travel between the two in spring and fall. In Nebraska, C. p. bellii often migrates several kilometres from shallow or dry marshes and basins to permanent water bodies during dry summer months (Ernst et al. 1994). Long-distance migrations are equally possible in the drier parts of this species’ range in Canada. Movements may be overland from one water body to another or linearly along streams (MacCulloch and Secoy 1983). Long-distance homing ability seems to be well developed in the Western Painted Turtle, with successful homing distances of up to 3km having been recorded (Gregory and Campbell 1987).
Small juvenile Painted Turtles feed primarily on tadpoles and invertebrates such as aquatic insects, crayfish and snails. When they grow larger they switch to bigger prey such as frogs and fish and they also scavenge (Gregory and Campbell 1987). As turtles mature and their growth rate declines, individuals become increasingly omnivorous, feeding on live animals and carrion as well as the abundant wetland plant life (Gregory and Campbell 1987). Cooley et al. (2003) suggested that northerly populations exhibit a greater degree of carnivory than southerly ones. Like most aquatic turtles, C. picta swallows its food with more ease when submerged because of its fixed tongue (Gregory and Campbell 1987). Feeding begins when water temperatures reach 15 to 18°C in April or May and ceases when temperatures drop below this threshold in September; feeding may also stop when water temperatures exceed 30°C (Ernst et al. 1994).
The egg stage is the most vulnerable phase of the turtle’s life cycle because: (1) predators can easily dig up the eggs; (2) nests are, generally, predictably situated close to the water’s edge or along roadsides; and (3) many wildlife species, including predators of turtle nests, travel along linear landscape features such as roads or shorelines (Spackman and Hughes 1995). Predation on Western Painted Turtle eggs is commonly high; up to 90%. For example, a family of skunks preyed on 80 to 100% of the Western Painted Turtle eggs along Elizabeth Lake in Interior B.C. during at least three consecutive years (Clark and Grueing 2002; Clarke pers. comm. 2004). Macartney and Gregory (1986) encountered 28 predator-destroyed nests in Kikomun Creek Provincial Park during a 3-month study. Predation rate on nests decreases with increasing distance from the edge of ponds (Kolbe and Janzen 2002b; Marchand et al. 2002) and is greatest on nests within 50 m of the water (Kolbe and Janzen 2002b; Marchand et al. 2002; Marchand and Litvaitis 2004). Nest distribution seems to affect predation, with clumped nests being preyed upon at a higher rate than scattered ones (Marchand and Litvaitis 2004). Aside from the pond edge effect, landscape composition (500-2,000 m from ponds) and the type of habitats surrounding ponds (up to 250 m from water) apparently have little influence on predation rates (Marchand and Litvaitis 2004).
Predators of painted turtle eggs include raccoons (Procyon lotor), coyotes (Canis latrans), mustelids (fishers, Martes pennanti; badgers,Taxidea taxus; otters, Lutra Canadensis; mink, Mustela vison; and weasels), skunks,black bears (Ursus americanus), squirrels, ground squirrels, chipmunks, corvids (ravens, Corvus corax, and crows, Corvus brachyrhynchos), and domestic cats and dogs (see Marchand and Litvaitis 2004; Clarke and Gruenig 2002; Maltby 2000). These species can also prey on hatchlings and small juveniles at the water’s edge. Predators of small turtles within the water include the semi-aquatic mustelids, raccoons, bullfrogs (Rana catesbeiana), great-blue herons (Ardea herodias), gulls and large fish. Mammalian predators (coyotes, raccoons and some mustelids) also feed on larger juveniles and adults, primarily when they are on shore. Otters kill hibernating turtles and can devastate local populations when the turtles overwinter in groups in exposed areas (Brooks et al. 1991).
Rates of parasitism may be high in shallow, warm water bodies. For example, 10 to 40% of adult Western Painted Turtles can be infested with leeches (Placobdell spp.) at any given location (MacCulloch 1981). Nine different species of Monogenea (Polystomoides pauli and Neopolustoma species), four species of Digenea (Eustomus chelydra, Spirochis kirki and S. parvus, Allassostomoides chelydrae), and three nematodes (Spiroxys contorta, Serpinema trispinosus and Amphibiocapillariaserpential) are known to parasitize Painted Turtles (Platt 2000). Leeches can transfer protozoan parasites to other individuals of the same or different species of turtles (Siddall and Desser 2001).
High elasticity of adult survival and low elasticity of fecundity in turtles implies that conservation efforts that reduce mortality of adults are likely the most effective way to stabilize declining populations (Heppell 1998). A barrier/wall-culvert system was introduced by the Florida Department of Transportation because of high numbers of roadkills (Dodd et al. 2004). This barrier system reduced mortality of adult turtles by 65%. B.C. Hydro’s Columbia Basin Fish and Wildlife Compensation Program (CBFWCP) has also been successful at protecting Western Painted Turtle females through various forms of fencing, crossing or interpretive signage and/or working with government to protect known nesting areas (R. Clark pers. comm. 2004). If an abundance of nesting habitat is available, especially beyond 50 m of the water line (where predation rates drop), this type of conservation strategy could be very effective at protecting local populations.
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