The marvelous eyes of the Osprey
Blog vol 6.42. The marvelous eyes of the Osprey
There are some amazing creatures with some crazy vision. I am a big fan of the show, Wild Kratts, where Chris and Martin use creature power discs to enable them to become creatures, such as an osprey (Season 3, Episode 7). Ospreys are raptors that have high-speed flight, sharp uniquely angled talons for gripping fish, and specialized anti-glare vision to see the fish through water reflections.
It is in the eyes. Like all raptors, in each eye they have two foveas (place on the retina of sharpest vision, humans have one fovea) for prey detection, and they have densely packed cones for finer acuity. Ospreys, sometimes called Seahawks because of their diet of live fish, have other unique adaptations.
1. Ospreys have three eyelids. The third lid is a nictitating (nictitate means “wink”) membrane which is semi-transparent and sweeps horizontally across the eye to protect the eye when fishing (and when feeding their rambunctious young) and to also act as goggles to see when beneath the water.
2. Ospreys are born with black eyes, then they change to blue, and then to amber brown.
3. Ospreys have four types of colour receptors, unlike humans who have three; the extra receptor gives them ultraviolet perception.
4. Ospreys have dark feathers in front of the eye which help reduce glare from the water surface.
5. Ospreys also perceive through the prismatic effect of the refractive index of the water to compensate for the true location of the fish under the water (try catching something under the water surface, not easy). In other words, their visual system compensates automatically to locate fish, ours does not .
Thay are so cool to watch. All you need is a good set of binoculars or a telephoto lens on a camera, a nesting site, and some time on your hands. There are elevated platforms on Christie Lake on Middletown Road outside of Dundas especially made for osprey nesting. You can visit anytime and watch the show, with the best time being when the fledglings are taking their first awkward flights. So special.
To think that this species was almost wiped out by the indiscriminate use of the insecticide DDT in the 1940’s and 50’s. Accumulation of DDT up the food chain resulted in reduced calcium absorption and thinner eggs and loss of hatchlings. Unfortunately, birds like ospreys, who only lay 1-3 eggs at a time, were almost wiped out. Fortunately, that has changed and we can continue to enjoy this marvelous creature.
Til next week,
The good doctor
