by Darcy Thomas
“There’s an Osprey” I pointed out to my sister as our kayaks sliced through the serene waters of Smith Lake. We stopped paddling and watched as this beautiful raptor circled the shallow waters of the lake scanning for fish beneath the surface.
Ospreys have incredible vision. Visual adaptations that allow them to spot fish below the water include two fovea in each eye that give them a wide angle of sharp focus, a structure in the eye called a “pecten”, composed of photoreceptor cells that enable greater visual resolution, and special muscles called Crampton’s muscles, allowing their ocular lenses to see prey at great distances. The dark feathers in front of the eye also reduce glare from the water.
Spotting a fish, he swept back his wings and plummeted toward the lake, swinging his legs forward at the last minute to enter talons first. He came up empty having missed the fish and was soon circling and scanning again. Once more he dove and came up without the prize. On the third dive the osprey plunged and disappeared underwater.
Osprey often get soaked catching a fish and are still able to fly away with their prey because their oily, dense plumage provides waterproofing. Occasionally, a large fish will pull an Osprey underwater completely. Ospreys weigh three to four pounds and are capable of carrying a fish equal to their own weight. They close their nares to prevent water from flowing in and are adapted with a nictitating membrane or semi-transparent eyelid that acts like goggles, allowing them to see underwater. They grasp the fish with reversible outer toes, two facing forward and two facing back, and tiny spines or “spicules” on the feet assist in gripping a slippery fish. On rare occasions the talons dig deeply into a fish that is too large for the Osprey to carry, and the spines and curved talons make it difficult to release. The bird can get pulled under the water by the heavy fish and drown.
As we waited for the Osprey to rise with his meal, the surface of the water calmed becoming glassy and smooth. It was taking too long.
“I think he’s drowning,” I said in alarm.
Osprey are designed for fishing and fish make up almost their entire diet. They are successful in their catch at least one in every four dives. Ospreys have long, powerful, narrow wings that help them lift from the water with a heavy fish in their talons. Fish are carried facing forward to minimize wind resistance, and are taken to a perch where they can feast or to a nest where they drop it for their chicks to eat.
We kept our eyes on the spot where the bird had gone under. As the seconds dragged on we wondered if we were about to witness the drowning of one of these amazing birds. Suddenly, in a great burst of water and wings, the Osprey emerged carrying a huge fish. His wings beat heavily as he struggled to rise above the lake’s surface. He kept hitting the water, and with agonizing effort, the Osprey carried his fish from the lake but only a few feet above the water. It was too much for him to gain lift. Dropping the fish, he flew to a distant tree to perch for a well-deserved rest.
Osprey are a conservation success story after recovering from a decimated population caused by use of DDT, which poisoned the birds and thinned the shells of their laid eggs. But the Osprey still faces challenges. They pick up baling twine and other discarded plastic lines to incorporate into their nests. Sometimes, as they become entangled in the twine, they suffer slow, painful deaths from starvation, injuries, infection, or immobilization. Baling twine is thin, plastic rope used to tie up hay bales and can be orange, blue, pink, or green. Last year, an Osprey died dangling from his nest at the Creston Fish Hatchery. In 2021, a chick from a nest in Charlo died after being entangled in baling twine. These tragedies are all too common, but also easily prevented. You can help by picking up twine and disposing of it where Osprey can’t get it. Help spread the word about baling twine and Osprey! Please visit https://www.owlresearchinstitute.org/osprey-and-baling-twine
References available upon request.