Seafinding in sea turtle hatchlings

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Seafinding in sea turtle hatchlings
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Seafinding in sea turtle hatchlings
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Silhouettes, Beach Slope, and Light Cues
When hatchlings emerge from their nests in the
dunes of the beach, what information could they
use to determine the oceanward direction?

• Towards land, the dunes and associated vegetation
  form a dark silhouette.
• The beach slopes down in the direction of the
  water.
• Ambient light is reflected from the ocean, making
  that region brighter.

http//www.unc.edu/depts/oceanweb/turtles/beach1.h
tml
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Seafinding experiments

• Hatchlings oriented down-slope when no light was
  present. If light was present and the horizon
  around the tank was level, hatchlings ignored the
  slope cues (implying that the slope cues aren't
  as important).
• Hatchlings oriented to the side of the arena
  where the intensity of light was the brightest.
• Hatchlings oriented away from dark silhouettes
  that were placed close to the horizon.

Salmon, M., Wyneken, J., Fritz, E., and Lucas, M.
(1992). Seafinding by hatchling sea turtles Role
of brightness, silhouette, and beach slope as
orientation cues. Behaviour 122, 56-77.
http//www.unc.edu/depts/oceanweb/turtles/beach2.h
tml
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Neural control architectures
Simple Braitenberg vehicle in sufficient for
sea-finding problem
turtles eye view of natural visual scenes
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Turtles Eye View of Natural Visual Scenes
From Witherington and Martin 1996
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Seafinding in sea turtle hatchlings
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Simple cross-wired solution is not robustunder
natural conditions

• Problems
• orders-of-magnitude variation in background
  intensity
• gradients too weak (resulting radius of
  curvature r too large)
• spatial and temporal input variability (scene
  structure, noise)

r
IL
IR

• Solutions
• sensory input ? internal model ? motor output
• optimal spatiotemporal filtering of visual input

velL
velR