Osprey (Pandion haliaetus)

Measurements: 0.55-0.58m long; wingspan 1.45-1.70m

ID: Distinctive long-winged raptor, with whitish plumage below making it resemble a large gull. Head white with dark stripe.

Several birds of prey catch fish to eat, but none do it more spectacularly, or more effectively, than the Osprey. This plunge-diving raptor is so successful that it occurs on every continent of the world except Antarctica, albeit locally in Europe. It is equally at home fishing over fresh or salt water, and it can nest anywhere from high in a tree to flat on the ground. So long as there are large fish to catch in large, clear, unpolluted waters, there are Ospreys.

By Judy Gallagher – Osprey – Pandion haliaetus, Everglades National Park, Homestead, Florida, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=66899521

Fish are difficult prey, tricky to catch and even more slippery to hold on to. Ospreys have several adaptations to cope with them, not least in their talons, their working tools. For one thing the Osprey’s legs and feet are long and very big, and fitted with sharp, hooked claws with a wide reach. And of the four toes, the outer one is reversible, meaning that two toes can face forward and two back, allowing an even spread. The toes are also interesting in having short 1mm long spines, or spicules, projecting from their lower surface; these stick into the fish’s scales, helping the Osprey to keep hold of its meal.

Fish can only be dealt with after they are caught, of course, and the Osprey’s method of hunting is simple enough. With its long wings designed for slow gliding and hovering rather than soaring, the Osprey rises to a height above the water where it can see fish coming to the surface – which can be as much as 70m up – and simply moves along slowly, checking below it, like a golfer looking for a lost ball. Once it locates prey it hovers on the spot and, more often than not, moves down a little before hovering again, fine-tuning its bearings. Once committed to the attack it closes its wings and plunges towards the surface and then, just a few metres from the waves, it suddenly lifts its wings and leads with its feet. The prey, which may be as much as a metre below the surface, is grabbed upon impact.

By Russ – Ding Darling, Florida – CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=63696719

Ospreys are not true water birds, and their first need upon procuring prey is to become airborne again. They do have special oily plumage to prevent being rapidly soaked, but they are not immune to drowning – there are several records of birds being dragged under by fish that were too big to carry. With a few powerful flaps they lift off the water, and very soon they manoeuvre the capture so that it is held under the belly with its head facing forward, torpedo-like. This reduces air-resistance as the Osprey flies to one of its favoured feeding posts to devour the meal.

Ospreys will catch any kind of fish that they can, although mainly in the range of 150-300g (up to 1.2kg has been reported). They are limited by the degree to which a species comes up to the surface, and are therefore mainly found over shallow waters. Their strike rate varies from fish to fish. Slow-moving species such as carp are caught, on average, on six out of ten occasions, whereas fast predators such as trout, only four times out of ten.

Ospreys are largely summer visitors to Europe, although a few do overwinter in the Mediterranean region. The bulk of the population leaves in September and arrives back in March, returning to the same eyrie and remaining with the same mate where possible. The nest is built up every year, and after many continuous seasons it can become very large indeed. 

From ‘Birds: A Complete Guide to All British and European Species’, by Dominic Couzens. Published by Collins and reproduced with permission.