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The sensory ecology of polarized light

For orientation, birds use a number of different compasses based on the geomagnetic field, stars, the sun and the related pattern of skylight polarisation. In collaboration with scientists at Eötvös University in Budapest we have performed measurements of polarized skylight under different sky conditions and studied the orientation of birds and insects.

Dark coat preferred over white

Horses with different  coat
Photo: Gabor Horvath

It has been shown that birds use polarized light for detecting open waters in high arctic pack-ice areas, and also that skylights affected by for example forest fire smoke have a disorienting effect on animal orientation. Furthermore, according to Icelandic Sagas, Vikings used a sunstone to tell the direction to the sun at sea while sailing in mist and under overcast conditions, a physical prerequisite which we have shown is reasonable given low degrees of linearly polarized skylight is transmitted through clouds.
 
Studying insects, we have found that tabanid flies (horse flies) use reflected linearly polarized light to find hosts for a blood meal, preferring horses with black coat reflecting linear polarized light, over horses with depolarizing white coat. We plan to continue this project with extended work on the sensory ecology and evolution of parasite-host interactions and measurements of polarized skylight during orientation studies. We will also study the use of polarized light cues for orientation and food detection in birds.

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Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden