Ospreys proficient at nabbing fish

Ospreys are fascinating birds. Their crisp plumage, large yellow eyes, loping flight and incredible hunting skills make them an interesting species to observe.

The population of these fish-eating hawks rebounded following the ban on DDT in 1985. They can now be commonly seen patrolling waterways and lakes across North America, with most large Alberta lakes and rivers supporting healthy numbers.

Ospreys build their nests in tall trees and on a variety of human-made structures, including oilfield equipment, buildings and power poles.

Power poles are dangerous, as the nests can catch on fire and the birds risk being electrocuted. To address this problem, power companies and local conservationists have worked together in many areas to place deterrents on poles and to erect wooden nesting platforms. These alternate nesting locations are readily used by the birds and represent a win-win situation for all involved.

Ospreys have remarkable adaptations that enable them to fish effectively. They can dive into the water from a height of 40 metres and will plummet, feet first, below the water surface to snag a fish.

They grab the fish with their sharp talons, then use the backward-pointing spines on the soles of their feet to prevent it from slipping out.

If the fish is large, they struggle to get airborne again. Interestingly, they maximize aerodynamics while in flight by using an opposable outer toe to rotate the fish, so it is facing forward as they fly.

The males provide most of the food for the female and young. He usually eats the head of the fish before delivering the rest of the carcass back to his family.

Since Ospreys arrive later in the spring than local Canada geese, ownership battles often erupt when an osprey pair discovers that a goose has taken up residence on “their” nest.

If the nesting goose refuses to leave, some pairs have been known to delay nesting until the goslings fledge.

Recent research using satellite transmitters has revealed that juvenile ospreys will wander, loiter and even get lost on migration, while adults fly faster and take more direct routes to and from their wintering grounds.

Our western birds overwinter in Central America, while eastern birds migrate all the way down to South America.

I have seen many osprey nests and have observed that the bulky nesting material often includes large tangles of discarded baler twine and fishing line.

At a nest near Sylvan Lake, I also noticed that one adult had a piece of twine wrapped around its foot. These are sobering examples of how discarded plastic poses a hazard to our environment and wildlife.

The next time you see an osprey fishing or sitting atop a nest, take a bit of time to observe and appreciate these magnificent wild neighbours.

Note: Ellis Bird Farm closes for the season Monday.

Myrna Pearman is the biologist and site services manager at Ellis Bird Farm. She can be reached at mpearman@ellisbirdfarm.ca.

 

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