Osprey Facts

Ospreys are large majestic birds of prey that were hunted to extinction in the UK a hundred years ago. Forty years later they made a come back and we have learnt a lot more about them by studying them since rather than shooting them first and asking questions later. The more we learn about this amazing species the more tools we have in the tool box to help them recover from world wide declines.

Here are some basic osprey facts.

Scientific Name: Pandion Haliaetus

Races or subspecies:

• Pandion haliaetus haliaetus : Europe, Asia, North Africa
• Pandion haliaetus carolinensis : North America
• Pandion haliaetus ridgwayi : Caribbean
• Pandion haliaetus cristatus : Australia, South-east Asia

Appearance:

• Head: White with speckled crown and black eye stripe.
• Body:  Dark brown upperparts, underbody all white, apart from rusty-buff to brown streaked breast band, more prominent in females, absent in some males.
• Flight feathers from below: Pale grey, barred overall. Dense black carpal patches and long black tips to primaries.
• Undertail: White and dark-barred.
• Eyes: Yellow (orange when young)
• Wings: Long and narrow with four long finger-like feathers.
• Adults: Like most birds of prey, the females are slightly larger and heavier than males, usually between 10% and 15%. 
• Juveniles: Similar to adult but lighter brown above, with feathers edged creamy white. Less marked below. Eyes orange.

Dark, orange eyes characteristic of juvenile ospreys                                                                                                             © Emyr Evans

Average measurements of an adult osprey:

• 	Male	Female
  Length (cms)	56-60	57-62
  Wingspan (cms)	147-166	154-175
  Tail (cms)	19-21	20-23
  Weight (kgs)	1.4-1.6	1.6-2.2

Age at first breeding: Average 3 (extremely rarely 2) to 7 years

• Clutch Size:Usually three, sometimes two, rarely four.
• Single brooded.
• Egg size:62-46 mm, slightly larger than a hens egg.
• Fresh weight of egg: 72 g
• Incubation period:35-40 days
  • Incubation by both sexes, but in the main the female.
• Fledging period: Average 53 days
  • Generally 49-56 days – males tend to fledge a little earlier than females
• Plumage:
  • First down plumage at hatching.
  • Second down from 11 days.
  • First complete feathers 42 days
  • Full adult plumage around 18 months.
• Food:
  • Exclusively live fish.
  • Salt and Freshwater prey taken.
  • Catches fish near surface, diving feet first. 
• Confusion Species:
  • Greater Black-backed Gull
  • Lesser Black-backed Gull
  • Heron

Osprey Trivia:

• Ospreys are the only bird of prey species in the world that feed exclusively on fish.
• Ospreys are found on every continent except Antarctica.
• British Ospreys usually migrate to West Africa during the winter, as our waterways stand a chance of freezing over. Most UK ospreys overwinter in Senegal, Gambia and Mauritania.
• Ospreys plummet feet first towards a single fish in the water from up to 40 metres.
• Osprey pairs that lose their eggs or young frequently build “frustration” eyries.
• Ospreys generally mate for life, unless one of the pair does not return. Occasionally they will “divorce” their partner if they are not satisfied with the way their mate behaves (a bit like humans!).
• Fledged osprey young sometimes visit nearby nests to be fed by other parents.
• Sometimes ospreys will bring objects to their nests as adornments. Dead crows have been recorded in Britain on a few occasions, in America they have recorded rag dolls, hula-hoops and toy boats!.
• Ospreys are often more bonded to their nest than their mate.
• Ospreys have four reversible toes, arranged in pairs. The first and fourth are directed pointing backward and the second and third pointing forward. Other birds that have this same adaptation are woodpeckers, parrots and owls.

The reversable toe arrrangement in osprey feet (Zygodactyly)                                                                                            © Emyr Evans

Egg Statistics ☛