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Sea birds hunting

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Sea birds hunting

Postby Lary » Wed Jul 03, 2013 1:12 pm

I was watching some sea birds hunting the other day, terns in particular and I was wondering, how do they perceive fish underneath the water surface?
The surface of the water is often choppy or churned up, plus the reflected light from the sky, yet they are still able to accurately get fish.
Last edited by ilago on Wed Jul 03, 2013 7:43 pm, edited 1 time in total.
Reason: Edit: Duplicate post removed
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Re: Sea birds hunting

Postby fsm » Wed Jul 03, 2013 4:41 pm

Seabirds such as terns and gulls that feed at the surface or plunge for food have red oil droplets in the cones of their retinas. This improves contrast and sharpens distance vision, especially in hazy conditions. Birds that have to look through an air/water interface have more deeply coloured carotenoid pigments in the oil drops than other species.

This helps them to locate shoals of fish, although it is uncertain whether they are sighting the phytoplankton on which the fish feed, or other feeding birds.

Birds that fish by stealth from above the water have to correct for refraction particularly when the fish are observed at an angle. Reef Herons and Little Egrets appear to be able to make the corrections needed when capturing fish and are more successful in catching fish when strikes are made at an acute angle and this higher success may be due to the inability of the fish to detect their predators. Other studies indicate that egrets work within a preferred angle of strike and that the probability of misses increase when the angle becomes too far from the vertical leading to an increased difference between the apparent and real depth of prey.

http://en.wikipedia.org/wiki/Bird_vision

Vision and Foraging in Cormorants: More like Herons than Hawks? (pdf)
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Re: Sea birds hunting

Postby Helix » Wed Jul 03, 2013 5:06 pm

I wonder how often they miss?!

This might be a situation where the reflective guanine in fish skin and scales work against the fish. That flash of silver close to the surface is a giveaway.

For a different style of fishing, have a look at the way skimmers get their food. They fly with their lower beak in the water. When they hit something, they snap the beak shut. The beak is asymmetrical --- the lower part is longer than the upper.

Here's a video of the American species: http://ibc.lynxeds.com/video/black-skim ... ming-canal
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Re: Sea birds hunting

Postby Lary » Sat Jul 06, 2013 4:23 pm

That is really interesting, thanks for the info!
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Re: Sea birds hunting

Postby roughbarked » Sun Jul 07, 2013 1:51 am

I wonder how often they miss?!


Birds standing in still or slow moving water probably hit more often and birds that dive into the sea have been filmed chasing the target down rather than spearing them direct but again it is the flash of silver that is likely to be the fish's downfall?
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