Ospreys are a bird of prey from the Accipitriformes family. These raptors are experts at hunting fish, which forms the backbone of their diets.
Ospreys are distributed across much of the world and are found on every continent except Antarctica. Identifying Ospreys is relatively simple due to their white bodies and contrastingly dark wings, but identifying juvenile Ospreys is a little more tricky.
Juvenile Ospreys quickly lose their natal down, which gives way to their juvenile plumage. Osprey juvenile plumage is similar to adult plumage, but their dark wings and upperparts are tipped with white edges.
This fine barring identifies late juveniles from mature adults. Additionally, juvenile’s white undersides have a buff-brown wash which looks dirtier than adults’ undersides, except when the adult plumage becomes worn and turns a similar color.
Another way to identify juvenile Ospreys is to look at their eyes. Juveniles have darker orange eyes, whereas adults have yellow eyes. Dark orange eyes with white-tipped, barred or spotted upperparts confidently identify a juvenile Osprey.
Of course, there is much more to learn about juvenile Ospreys - read on to find out!
Close up of a young Osprey fledgling in the nest with spread wings
Ospreys breed as early as March. Baby Ospreys emerge from their eggs between March and May and are covered in a thick natal down that lasts until May to July. Ospreys molt their natal down after just a week or two, and their juvenile plumage is complete after around 50 to 60 days, when most chicks begin to fledge.
Juvenile Ospreys look remarkably similar to adults, with only minor differences. One of the key differences is their white barred spotted or tipped wings and upperparts. In addition, since adult Ospreys have dark upperparts, the white juvenile barring is quite conspicuous compared to the more darkly colored uniform adults.
Also, juveniles’ upperparts are lighter brown than adults. It’s very tricky to distinguish between juvenile female and male Ospreys, but females are up to 20% larger with longer tails and sometimes have darker feathers on the chest and lower neck than males.
Juveniles have a buff brown across their underside, which shows up against their white bodies. This brownish tinge helps identify juvenile Ospreys from adults while they’re in flight.
Juvenile plumage lasts for around 18 months, at which point Ospreys molt into their adult definitive plumage.
Juvenile Osprey perched on a post
Young Ospreys grow quickly, attaining around 90% of their adult size and weight by the time they fledge after 50 days or so.
A fledged juvenile Osprey that can fly competently is a similar size to an adult, measuring around 60cm (24in) long with a wingspan of 180cm (71in).
Juvenile Ospreys undergo around three highly variable molts that see them transition from their basic juvenile plumage to their definitive adult plumage.
Firstly, Ospreys molt their natal down, which happens within just days of hatching. Ospreys possess their juvenile plumage after around 60 days, which is when they’ll begin to fly competently.
The first juvenile molt occurs around December and includes around 35% of feathers on the body and upperparts. The second molt and third molts occur throughout winter and into spring of the second calendar year.
Juvenile plumage may persist for over two years but is typically replaced by adult plumage after 18 months or so.
Juvenile Osprey in flight
Juvenile Ospreys waste no time in practicing their fishing skills. One study in Florida found juveniles attempting to catch fish just five days after fledging.
Ospreys made the first successful catch 11 days after fledging, and all Ospreys in the study had succeeded in catching a fish by around day 21.
Juvenile Ospreys attempt to catch the same fish as adults but aren’t fully competent for about 5 to 6 months. Interestingly, some juvenile Ospreys were found foraging with their siblings and are thought to learn some foraging skills by observing them.
Juvenile Osprey with a caught fish from the water
In one North American study, juvenile Ospreys made their first catch 11 days of fledging when they were just over two months old. All juvenile birds in the study had successfully caught a fish by day 21.
Ospreys’ hunting abilities are considered innate, as human-released birds seem to hunt by instinct without watching their parents. However, some Ospreys are observed watching their siblings hunt, from whom they may learn some foraging skills.
Ospreys have a lengthy fledging period of just over 50 days. After fledging, they remain close to their parents for another month or two, or up until it’s time to migrate in early-to-mid fall.
Juvenile Ospreys remain in their wintering grounds for 1 to 2 years, while adults return the following spring to breed. So, young Ospreys become independent fairly quickly, especially compared to other young raptors that may remain with their parents for a year.
Three Juvenile Ospreys at the nest with adult female parent
Juvenile Ospreys migrate in fall, but unlike adults, they remain in their wintering grounds for more than one winter. In fact, some birds in Europe were found to winter for two or even three wintering seasons before returning in spring.
Juveniles also take different migratory routes and tend to follow coastal or over-water routes rather than travel across the land.
Osprey migration is complex, and the reasons why juvenile Ospreys behave differently during migration and wintering are poorly understood. Longer migratory routes might indicate that birds are practicing their long-distance flight, for example.
Close up of a perched young juvenile Osprey
Ospreys remain in the nest for about 50 to 55 days. Both parents take close care of the young. After fledging, young Ospreys quickly become independent and can hunt after two to three weeks.
They remain close to their parents for another two months or so until it’s time to migrate in fall/autumn. Juvenile Ospreys usually migrate alone, whereas adult Ospreys sometimes form small groups.
Ospreys fully molt their juvenile plumage after around 1.5 to 2 years. After that, they still have a other 1 to 2 years before they’re sexually mature and ready to breed.
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