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The Ultimate Guide to Ospreys

Written by: Thursa
Published: 21st March 2019

Last Updated on

March 18th marks the beginning of World Osprey Week, as we celebrate the welcome return of ospreys to the lochs and estuaries of Scotland. These imposing and stunning raptors are a rare treat for bird watchers. Only a half-century ago they were extinct here, but now, thanks to incredible conservation efforts they are making a comeback.

 
 

01. How To Tell It’s An Osprey

Fact 1: Female ospreys are 20% larger than males.
In the high blue distance, soaring over the sea, it looks almost gull-like, but as it approaches you see feathered fingers at the wing tips. Buzzard? No, bigger than a buzzard. Slightly longer body and much longer wingspan – a wingspan of nearly 6 feet! As it flies overhead its full magnificence is revealed. Bright yellow eyes set in what appears to be a thick black stripe wrapped around its head like a ragged highwayman’s mask. The unmistakeable face of an osprey.

Muscular jointed wings make a wide M shape against the sky, with a clean white underbelly, and barred brown markings on the underside of the wings and tail. If it’s a female, she will have a speckled brown ring around her shoulders like a necklace.

The face and neck feathers are thick, white and fluffy and the top half of its grey-black beak points downwards rather disapprovingly at the end.

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02. Why Ospreys Are So Rare

Fact 2: Ospreys live for 26 years on average.
Well might they disapprove; they were hunted throughout the British Isles by our Victorian ancestors until 1916, when the species became completely extinct. Victorians, not content to see this amazing creature in the wild, liked nothing better than to stuff an osprey and put it on display in their living rooms.

Osprey eggs were also highly collectible, and as they became rarer the price got higher. Thieves went to great lengths to get their sweaty hands on an osprey egg. Even today, though the ospreys have tentatively returned to our shores, many of their nesting sites need protection.

It wasn’t until 1954 that a single pair of ospreys began to nest in Speyside. The last record of Ospreys breeding in that area had been in 1899, so you can imagine the amazement of bird watchers. Conservationists at the Royal Society for the Protection of Birds launched ‘Operation Osprey’, and mobilised everything they could to protect the birds as they bred.
This led to more sightings and now Scotland has a growing population. But elsewhere in the British Isles the numbers remain scarce. In Glaslyn Valley in Wales a rare nesting pair are given round the clock surveillance to protect them from potential egg stealers.

Because of the rareness of these birds and their imposing presence, ospreys have reached a kind of mythical status. The sight of an osprey in the sky more than equals expectations.

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03. Where Do Ospreys Live?

Fact 3: During incubation it is mostly the female who stays on the nest while the male hunts. When he returns to the nest with his catch, he will incubate the eggs while the female flies off to stretch her wings and hunt for herself.
Ospreys always settle near water – rivers or inland lakes, coastal lagoons and estuaries. They make their nests on sea cliffs, in the tops of trees or on man-made structures like pylons. They like a high flat position with 360° visibility.

Having established their nest in the first season, sometimes using an abandoned nest and ‘redeveloping’ it, adult pairs return every March or April to the same nest to breed. A pair of ospreys mate for life and every year will add to and develop their nest. It is possible to see a well-established nest 6 feet in diameter and up to 13 feet deep. Almost the size of a New York starter apartment.

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04. Where Do Ospreys Migrate?

Fact 4: On migration flights ospreys travel extraordinary distances. One female was tracked from Speyside to Gambia, a journey of 4232 miles, making the whole trip in just 7 days!
In mid-august they take off on the long flight to their African winter home; most settle on the North African coast, but some will cross the Sahara desert pressing on in to West Africa, while others turn westward to winter in Spain or Portugal.

Migrating birds have an innate internal GPS system which appears to be fully operational even on their first migration. Research suggests that during the first summer of their lives the birds learn the layout of the stars, especially the North Star, enabling them to navigate. We know about the presence of magnetite receptors in the beaks of all migratory birds, including ospreys. These receptors manage – we don’t yet know how – to sense the Earth’s magnetic fields and use these for navigation, setting a precise course back to the same nest each season.

It’s a remarkable feat, considering that without a map to guide us we humans would do far worse finding a single nest on a large continent. Strong evidence suggests that scent plays an important role, as well as topographical landmarks – the meandering of rivers, or the line of a mountain range. They may be aware too of infra-sound: geological creakings, the patterns of wind and sea, and the sub-atomic sighs that human ears are too dull to comprehend.

Sometimes the vagaries of weather and solar activity can interfere with this navigational precision. Gales can blow them off course, and solar wind surges can distort the Earth’s magnetic field. The sight in 1954 of a pair of ospreys in Speyside may have been the result of migrants being blown off course, or confused by solar activity on their way to Scandinavia. Lucky for us.

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05. Is Osprey Vision Better Than Humans?

Fact 5: Ospreys have a special transparent eyelid than protects their eyes when they are diving into water. They can also close their nostrils!
Like most raptors (birds that eat prey) ospreys have binocular vision. That is their eyes are sufficiently close together to enable them to see as we do. Birds that are predated tend towards monocular vision, the ability to see objects with one eye at a time, to almost have eyes in the back of their heads – useful if you’re potentially someone’s lunch.

Monocular vision is by no means a lesser ability though. Pigeons for example have been proved to see twice as well through one eye than they can through their limited binocular range. The opposite is true of humans.

An osprey’s round yellow eyes have black pupils which dilate from 2.5mm to 5mm wide, the same sized pupil as a human eye.
There is much ornithological argument about how well ospreys, and indeed all raptors, can see. Many fabulous claims are made, that they have from 3.5 to as much as 8 times better vision than humans.

In truth we know certain facts, the rest is conjecture. The facts are that raptors have a much denser supply of photoreceptors packed into their tiny retinas than humans do. That, and the shape of their eyeball, more tube than ball, means an osprey eye has a greater magnifying effect, or depth of field, than a human eye.

The downside is that their eyes, not being spherical, don’t revolve in their sockets like human eyes do, so are not capable of the almost instant visual field of 120° that humans enjoy. It’s like comparing apples and oranges. Human eyes have evolved to do better at scanning wide landscapes for predators or prey, osprey eyes for zooming in on fish.

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06. What Do Ospreys Eat?

Fact 6: Ospreys have been known to dive up to 3 feet below the surface of the water in pursuit of a tasty fish.
You’ve got it. Fish. An average adult will catch 2 to 3 fish a day, and 5 or more when they have a family to feed. One of the ospreys at Loch Garten RSPB Reserve in Abernethy, a father of 3 chicks named Odin, caught 9 fish in one day, setting an old-time osprey record. (They probably still talk about it around the nest).

From rivers they enjoy trout, perch or pike, and smaller fish, while from a sea loch or estuary they will hunt for flounder and mullet. Very occasionally they go after salmon.
Ospreys, for their skills, are sometimes called Sea Hawks. The Italians call them Falco Pescatore, the fisher falcon. Though it’s not strictly of the falcon order. Ospreys (Pandion haliaetus) belong to a genus all their own called Pandion, from the order of Accipitriformes, an order that includes hawks, eagles and vultures – but not falcons. Falcons and kestrels belong to Falconiformes, an order that more closely resembles parrots.

Occasionally ospreys will have a nibble on the odd rodent, or small mammal, or even another bird. But only when they are in Africa. In the UK they always eat fish. They just can’t get enough. And what well adapted fishers they are too. Their wings are so powerful they have been seen to grab a large fish up to 4 pounds in weight, almost equal the body weight of the bird (though they usually go for fish between 5 and 10 ounces), and while the fish pulls desperately for deeper waters, the osprey uses its strong and massive wingspan to get itself out of the water and airborne again.

Like the owl, an osprey’s outer toe is fully reversible, making it ideal for grabbing and holding on to a slippery fish. Taxonomists, who often like to decide what genus a bird belongs to by the arrangement of its toes, were very puzzled by this, which is why Pandion haliaetus has its own genus.

The battle between osprey and fish can sometimes end with the fish dragging an older, perhaps weaker osprey down to the bottom of the sea or river to drown. It is not uncommon for old ospreys to end their lives this way. A large salmon or sturgeon has from time to time seen off an overreaching osprey.

The black markings between or above the eyes in the centre of the head are thought to reduce glare from the surface of the water as an osprey dives, and its feet are perfectly adapted with adhesive miniature spines, called spicules, on the undersides, and long curved claws so that they will not let go; once they have grabbed a fish, that fish has had its chips.
As they take off again with their prey the osprey will turn the fish’s head so it faces forward and pierce its brain with a claw, both to stop the fish flailing about and to reduce wind resistance.

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07. Where To Find Ospreys In Scotland

Fact 7: The collective noun for osprey is a ‘duet’, referring perhaps to their monogamous natures.
Over the latter part of the 20th century breeding pairs of Osprey have increasingly returned to their historical nesting sites in Scotland. With careful conservation, the original 1954 pair in Speyside have founded a dynasty of around 32 nesting pairs. A collection of ospreys regularly breed at Rothiemurchus in Aviemore, where intrepid wildlife photographers are invited to shoot for beauty instead of sport.

Loch Garten in Abernethy, Loch of the Lowes in Perthshire, the Tweed Valley Osprey Project in Borders, and Caverlock Wildfowl and Wetlands in Dumfries, are all doing their part in welcoming back Ospreys, and numbers in Scotland have swelled to around 224 nesting pairs in total. Though there is still more work to do to make the population sustainably robust, those early pioneers of RSPB’s ‘Operation Osprey’ should be proud.

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08. Sightings at Highland Titles

Fact 8: The wings of an osprey contain more feathers and are generally more powerful than other large raptors, so they can catch and carry off larger quarry.
After building our lochans in the Highland Titles Nature Reserve, and stocking them with fish, we were delighted in 2016 by our first sighting of an osprey hunting in our very own Loch Fois. They have been returning every year since, using the reserve as part of their hunting ground. An osprey’s hunting grounds are roughly within a 20 mile radius of its nest, but it will go further afield. So we think our osprey might be from a nesting site in Loch Arkaig on the edge of Loch Linnhe, about 22 miles from Highland Titles, as the crow (or osprey) flies.

As Ospreys gradually died out in the early 20th century, a breeding pair still used to return annually to Loch Arkaig in Lochaber, until 1908. After that a single osprey kept returning to the same nest until 1913, having lost his mate in ways we cannot know. One spring he didn’t turn up at all, and the surface of Loch Arkaig felt the beating wings of osprey no more. Until now.

In 2016 Loch Arkaig came under the care of the Woodland Trust. Noticing that ospreys were starting to return to the area and attempting to breed, they took steps to help. Ospreys like the reassurance of a ready-made nest, so volunteers built nesting platforms and secured them to the tops of Scots Pine trees. The naturally flattened shape of the Scots Pine is ideally suited to the sort of tree top nest favoured by an osprey.

In 2017 they had their first settler, a single male. They named him Lonesome Louis. Three weeks later he had found himself a mate, whom the volunteers called Aila. They laid their first 3 eggs, and produced 2 chicks: Lachlan and Pean.

Unfortunately Pean was killed by a power line while wintering in Spain in January 2019. He had become a local celebrity in the Marjal de Pego-Oliva Natural Park, a Spanish wildlife reserve, but landed on an overhead cable that was not properly insulated and was tragically electrocuted.

After Louis and Aila lost all their eggs to a pine marten raid in May last year, and now this, it brings home to us how fragile the lives of these magnificent birds can be. More breeding must be encouraged to ensure their continued survival.

 
Picture of the osprey at the Highland Titles Nature Reserve.

Highland Titles is supporting Ospreys

Stewart Borland, Estate Manager on the reserve, has been working on this very problem and over the winter he and the hard working volunteers on the Highland Titles Nature Reserve have built their first osprey nesting platform on the top of a spruce. Now it is a game of wait and see as we eagerly await the return of the ospreys from Spain and Africa in March and April. Any day now! Stewart says:

“Caring for the land over the last decade has inevitably progressed to caring for the wildlife, and endangered animals has become a priority for us here at Highland Titles. The creation of Loch Fois, which we then stocked with wild brown trout was the catalyst, and I can’t describe how excited I was to see the first osprey on the Reserve, and to have it return three years in a row is a testament to the work we’ve done here.”

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About the author

Written by: Thursa


Comments on this post

  • Lady Julia
    07/04/19 - 19:28

    What a wonderful write-up! Enjoyed learning about this wonderful creature and efforts of so many to bring back this species. Keep up the good work, and here’s hoping for that mate to show up.

  • Polly Turner
    25/09/19 - 14:18

    An interesting and informative read. Just to say that in 2017 Aila and Louis produced one chick, Lachlan, Pean was from a second nest at Loch Arkaig.

  • susan gilbert
    25/09/19 - 19:50

    Thank you, what a lovely write up! In 2019 Louis and Aila had two chicks, Maillie and Rannoch, who were ringed and successfully fledged. There are photos on Friends of Loch Arkaig facebook page.

  • Liz Bracken
    26/09/19 - 11:54

    An interesting read, but Loch Arkaig can hardly be described as being “on the edge of Loch Linnhe”. It’s approximately ten miles as the crow flies. It is however less than two miles from Loch Lochy a freshwater loch in the Great Glen. Also the nesting platform at Loch Arkaig was occupied by breeding ospreys long before 2016. In the two years before Louis and Aila took over the nest, the resident ospreys had failed to produce chicks and did not return in 2017. Ospreys have been breeding in this area for at least ten years to my knowledge and probably more. As someone has previously mentioned Louis and Aila only fledged one chick in 2017, Lachlan. Pean came from a nest at the other end of the loch. I’m interested to know where Loch Fois is located as I can’t find any reference to it? Here’s hoping you have success with your new osprey nesting platform.

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