A compass without a map: tortuosity and orientation of eastern painted turtles ( Chrysemys picta picta) released in unfamiliar territory I.R. Caldwell and V.O. Nams Abstract: Orientation mechanisms allow animals to spend minimal time in hostile areas while reaching needed resources. Identification of the specific mechanism used by an animal can be difficult, but examining an animal’s path in familiar and unfamiliar areas can provide clues to the type of mechanism in use. Semiaquatic turtles are known to use a homing mechanism in familiar territory to locate their home lake while on land, but little is known about their ability to locate habitat in unfamiliar territory. We tested the tortuosity and orientation of 60 eastern painted turtles (Chrysemys picta picta (Schneider, 1783)). We released turtles at 20 release points located at five distances and in two directions from two unfa- miliar lakes. Turtle trails were quite straight (fractal dimension between 1.1 and 1.025) but were not oriented towards water from any distance (V-test; u < 0.72; P > 0.1). Turtles maintained their initially chosen direction but either could not detect water or were not motivated to reach it. Furthermore, paths were straighter at larger spatial scales than at smaller spatial scales, which could not have occurred if the turtles had been using a correlated random walk. Turtles must there- fore be using a reference stimulus for navigation even in unfamiliar areas. Re ´sume ´: Les me ´canismes d’orientation permettent aux animaux de passer le moins de temps possible dans les espaces hostiles, alors qu’ils recherchent les ressources qui leur sont ne ´cessaires. Il peut e ˆtre difficile d’identifier les me ´canismes spe ´cifiques utilise ´s par un animal, mais l’examen du trace ´ de ses de ´placements en terrains familier et inconnu peut fournir des indices sur le me ´canisme en question. Il est bien connu que les tortues semi-aquatiques, se de ´plac ¸ant au sol sur un ter- ritoire familier, utilisent un me ´canisme d’orientation pour retrouver leur lac d’origine; mais, on sait peu de choses sur leur habilete ´a ` trouver un habitat dans un territoire non familier. Nous avons teste ´ la tortuosite ´ et l’orientation chez 60 tortues peintes de l’est (Chrysemys picta picta (Schneider, 1783)). Nous avons rela ˆche ´ les tortues a ` l’un de 20 points de libe ´ration. Ces points de libe ´ration se trouvaient a ` cinq distances et dans deux directions par rapport a ` deux lacs non familiers. Les trace ´s des de ´placements des tortues sont remarquablement rectilignes (dimension fractal de 1,1 a ` 1,025), mais ils ne sont pas oriente ´s vers l’eau, quelle que soit la distance (test de V; u < 0,72; P > 0,1). Les tortues maintiennent l’orientation choisie initialement et elles n’arrivent pas a ` percevoir la pre ´sence d’eau ou alors elles ne sont pas enclines a ` s’y diriger. De plus, a ` des e ´chelles spatiales plus grandes, les trace ´s des de ´placements sont plus rectilignes qu’a ` de plus petites e ´chelles spatiales, ce qui ne se produirait pas si les tortues se de ´plac ¸aient selon un trajet ale ´atoire corre ´le ´. Les tortues doi- vent donc utiliser un stimulus d’orientation dans leurs de ´placements, me ˆme en terrain non familier. [Traduit par la Re ´daction] Introduction To survive and reproduce, animals must locate necessary resources (i.e., food, shelter, others of the same species). Simply depending upon random movements for this purpose can be energetically inefficient. For this reason, most ani- mals have evolved mechanisms and strategies to orient to- wards goals in their environment (Able 1991). When orientation is towards the site where an animal lives and has its shelter, den, or nest, it is referred to as homing (Papi 1992). If an animal is displaced far enough from where it lives that its home location is no longer detectable, or if its home is destroyed, the goal of orientation becomes habitat rather than home. Although the goal has changed, the princi- ple remains the same. The animal must locate suitable habi- tat as quickly as possible or risk death. This is especially important in situations where there are well-defined patches of suitable habitat separated by inhospitable or unfavourable areas. Animals use various orientation mechanisms to locate the nearest habitat patch. Mechanisms proposed for turtles in- clude geotaxis (movement either up or down an incline; Em- len 1969; DeRosa and Taylor 1982), olfaction (Emlen 1969; Graham et al. 1996; Lebboroni and Chelazzi 2000), use of light characteristics (movement towards or away from light, orientation using gradients of light polarity or wavelength; Yeomans 1995; Lebboroni and Chelazzi 2000), use of local topographic landmarks (Emlen 1969), use of a sun compass (DeRosa and Taylor 1976, 1982), and use of a magnetic compass (Mathis and Moore 1988). The first three of these suggested mechanisms (geotaxis, Received 24 November 2005. Accepted 21 June 2006. Published on the NRC Research Press Web site at http://cjz.nrc.ca on 13 September 2006. I.R. Caldwell 1,2 and V.O. Nams. Department of Environmental Sciences, Nova Scotia Agricultural College, Box 550, Truro, NS B2N 5E3, Canada. 1 Corresponding author (e-mail: i.caldwell@fisheries.ubc.ca). 2 Present address: Project Seahorse, Fisheries Centre, University of British Columbia, 2202 Main Mall, Vancouver, BC V6T 1Z4, Canada. 1129 Can. J. Zool. 84: 1129–1137 (2006) doi:10.1139/Z06-102 # 2006 NRC Canada