Notes on the movement and aquatic behavior of some kinosternid turtles
Notas sobre el movimiento y comportamiento acuático de algunas tortugas kinostérnidas
Gerardo Antonio CORDERO1 and Christopher W. SWARTH2
1 Department of Ecology, Evolution, and Organismal Biology, Iowa State University. 251 Bessey Hall, Ames IA, 50011, USA. E–mail: gcordero@iastate.edu.
2 Jug Bay Wetlands Sanctuary, Anne Arundel Recreation and Parks. 1361 Wrighton Road, Lothian, MD 20711, USA. E–mail: cswarth@jugbay.org.
]]>Recibido: 06/09/2009
Aceptado: 11/01/2010
RESUMEN
Las tortugas semi–acuáticas de la familia Kinosternidae han evolucionado varias adaptaciones en respuesta a cambios ambientales desfavorables, los cuales incluyen el movimiento terrestre de larga distancia en búsqueda de refugios durante sequía, y la tolerancia a altos incrementos de salinidad acuática. Sin embargo, el comportamiento y movimiento acuático de estas tortugas ha recibido poca atención.
The behavior of kinosternid turtles is characterized by long distance terrestrial movement in response to fluctuating aquatic conditions. For instance, Ernst et al. (1994) speculated that Kinosternon flavescens was capable of traveling as far as 8 km on land based on its presence in farm ponds and the location of the nearest permanent body of water. Hall & Steidl (2007) observed movements of 500 m or greater by Kinosternon sonoriense in desert springs, including movements by adult males of up to 2.7 km. Stone (2001) also reported evidence of long distance movement by K. sonoriense individuals, of which 13 traveled distances greater than1 km. In Mexico, Kinosternon leucostomum individuals occupying a temporary lake were reported to travel distances of up to 600 m to nesting and aestivation sites (Morales–Verdeja & Vogt 1997). Similarly, 17 Kinosternon scorpiodes traveled distances of up to 500 m away from a riverine marsh during the dry season in Costa Rica (Teska 1976).
Terrestrial movement has been studied extensively in Kinosternidae of eastern North America, where most observations have taken place within ephemeral bodies of water and adjacent terrestrial habitats. As a result, recorded long distance movements were associated with drought conditions or interpond migration. During the latter, the greatest terrestrial distance traveled by K. subrubrum was estimated at 900 m (Larese–Casanova 1999). Long distance movement is not restricted to the terrestrial environment in this family, and aquatic movement has received little attention. Nevertheless, a study of Sternotherus odoratus provided an estimate of mean aquatic home range size of 155 ha (minimum convex polygon) for males (Edmonds 1998). Additionally, homing behavior studies of this species demonstrated its ability to travel up to 1.1 km in water (Adres & Chamber 2006).
In addition to exceptional movement capability, kinosternid turtles are adapted to variable salinity conditions. Such is exemplified by K. scorpiodes of San Andres Island (Forero–Medina et al. 2007), which is located at approximately 180 km due east of the Nicaraguan Coast. However, in comparison, more information is available on estuarine kinosternid turtles of North America. The presence of K. subrubrum on Atlantic coastal barrier islands has been well documented (see reviews by Gibbons & Coker 1978; Mitchell 2007). Also, there is evidence from physiological studies to suggest that kinosternid turtles are better suited to low salinity or brackish water conditions than most freshwater turtles of the North American Atlantic coast (Dunson 1986; Dunson & Seidel 1986). These studies focused on Kinosternon baurii, and subsequent behavioral work revealed the use of terrestrial retreats in response to increasing salinity levels (Dunson 1981).
]]> Observations of behavioral responses to fluctuating aquatic environmental conditions, though not related to salinity, have been made for Kinosternon subrubrum on the Coastal Plain of Maryland, USA (pers. obs.). During low tide cycles a significant area of a freshwater marsh was drained and exposed for periods lasting up to 4 hrs. Then, observed turtles sought cover in mud or decaying vegetation. While in a burrow form, some turtles created a small opening in the mud for breathing and remained still. Presumably, burrowing behavior would serve as a predator avoidance or thermoregulatory strategy. On the other hand, turtles appeared to be more active and were, in some cases, observed swimming during high tide cycles. Often, turtles would lodge themselves tightly through the stems of Nuphar advena and Peltandra virginica as they maintained a firm grip with their forearms. Such action would function positively in resisting current velocity and water level fluctuations given that this species is not optimally adapted for swimming (Davenport et al. 1984). Unlike most freshwater turtles of the region, K. subrubrum rarely basks, but individuals were most frequently observed doing so during high tides.It is possible that adaptive strategies for coping with estuarine bimodal disturbance regimes may vary within and among populations. For instance, it is not clear whether K. subrubrum shifts its position in conjunction with low tidal cycles as an alternative to burrowing, and behavioral responses of populations in high salinity estuaries may resemble those of K. baurii. Additional observational studies of other kinosternid species, particularly in the neotropics or in coastal zones, may reveal similar or novel adaptive strategies in response to fluctuating aquatic environments.
ACKOWLEDGEMENTS
Observations of K. subrubrum were made while conducting research in the Jug Bay Wetlands Sanctuary, Maryland, USA; we thank the staff and volunteers for their support. Funding was provided by the Friends of Jug Bay Research Fellowship.
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