Fig. 2: The placement of the magnets (and shams) on the anterior carapace of hatchling (a) Blanding’s turtles and (b) snapping turtles showing the maximum distances from the magnet to the tip of their snouts (photos by Jerry Olson).<\/p><\/div>\n The research group looked at a few different categories of hatchling turtles for testing: Na\u00efve hatchlings that had never been exposed to environmental cues, arena-experienced hatchlings that were able to roam the arena before testing, and natural-experienced hatchlings that were captured while dispersing from their nests in the wild. Half of the turtles in each group\u00a0had magnets glued onto their backs to disrupt the Earth\u2019s magnetic field, while the rest had shams as a control. The first test arena consisted of a 100-m diameter mowed field, with open, light horizons on the East and West sides, and trees on the North and South sides that created a dark horizons. These different horizons were created to mimic the typical environmental cues for the two turtle species (light for snapping turtles and dark for Blanding\u2019s turtles). Other arenas were constructed that had tall corn crops on all sides that blocked the horizon. Groups of hatchlings were released into the arena, and their location was recorded after 1 hour. The researchers were most interested to see if the hatchlings\u2019 movements had directionality meaning they had a target location. The use of a corn field arena also allowed the researchers to disrupt the turtles\u2019 visual cues and only look at the possibility of a magnetic compass.\u00a0<\/strong>The researchers hypothesized if hatchlings did have a magnetic compass, then the turtles with magnets disrupting the magnetic field would not be able to maintain their previous heading compared to the control groups.\u00a0<\/strong><\/p>\n Fig 1. Aerial photograph showing the placement and shape of the (a) field arena in relation to the large dark tree rows and open ends of the field and (b) the corn arenas in 2012 and 2013 (hexagon=release area, and horizontal arrows indicate the location of irrigation wheel tracks and indicate the primarily E-W orientation of the corn rows).<\/p><\/div>\n They\u00a0found that overall, visual environmental cues rather than a geomagnetic sense were the most important factors in hatchling turtle orientation.<\/strong> Na\u00efve turtles released into the field arena exhibited directionality towards the man-made horizons, but this\u00a0was not seen in those released in the corn arena. The corn arena blocked the typical visual cues that allows the turtles to have a target location, so their dispersal was more random.\u00a0The arena-experienced group did show more directionality in the corn arena compared to the na\u00efve group, meaning that they were able to learn directionality from their short dispersal into the field arena. Tests with natural-experienced turtles showed that a geomagnetic compass was not used as they did not orient themselves towards the horizons created in the arena but instead maintained the previously established orientation when released into either arena. This orientation was instead based on their previous knowledge of the relation of the sun to their target location.\u00a0The presence or absence of a magnet had no effect on the directionality of any of the hatchling groups\u2019 movements.<\/strong><\/p>\n The researchers concluded that freshwater turtle hatchlings rely on a sun compass rather than a geomagnetic compass to orient themselves towards target habitats. This reliance is learned, however, as natural-experienced turtles could maintain the proper dispersal heading rather than move towards the man-made\u00a0horizons in the arena. The results of this study do not prove that a geomagnetic compass does not exist in freshwater turtles.<\/strong>\u00a0They\u00a0instead highlight\u00a0the importance of environmental cues in a hatchling\u2019s ability to orient itself in the proper direction.\u00a0<\/strong>Hatchlings learn from their surroundings, and use the sun to orient and navigate towards target areas. They can use this knowledge later on in life when they are displaced or need to travel to important areas again. More studies exploring the possibility of a geomagnetic compass in freshwater turtles should be done to confirm or deny its use and presence.<\/p>\n <\/p>\n For more information about this topic\u00a0see the full article:<\/strong><\/p>\n Congdon, J. D., Pappas, M. J., Krenz, J. D., Brecke, B. J., & Schlenner, M. (2015). Compass Orientation During Dispersal of Freshwater Hatchling Snapping Turtles (Chelydra serpentina) and Blanding’s Turtles (Emydoidea blandingii). Ethology<\/i>, 121<\/i>(6), 538-547.<\/strong><\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" We\u2019ve all heard of the five senses: sight, touch, smell, sound, and taste. Some animals, such as certain types of fish, reptiles, or mammals,\u00a0can also use an internal compass to navigate through their environment. This can be in the form … Continue reading ![\"Screen](\"http:\/\/pages.vassar.edu\/sensoryecology\/files\/2015\/05\/Screen-Shot-2015-05-13-at-11.27.13-PM.png\")
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