Facts about Osprey Lifecycles

Dyfi Osprey Chick in nest

Fact 51

Ospreys can live for over 25 years. The survival rate for youngsters in their first few years of life is poor - only a third make it back to the UK as two-year-olds. However, the return rate of adults of breeding age is much higher than this. Established and experienced ospreys have a successful return rate of 90%.

Fact 52

Ospreys do not generally return to their breeding grounds until they are two or three years old. It is rare for returning two-year-olds to breed - they use their second year to search around for nest sites and mates, although there are examples of ospreys having successfully bred at two years old, but these are rare. The average age is more like four or five years old.

Fact 53

Male ospreys display strong natal philopatry, this means that they return to the area (or more precisely, colony) where they were born. Female ospreys are less philopatric and will range further afield from their ancestral areas.

Fact 54

Ospreys typically lay a clutch of two or three eggs. On the Dyfi we have had a number of years where just two eggs have been laid and two chicks raised, but we've also had three fledglings (2011, 2015 and 2017). There are occasional records of ospreys laying four eggs, this happens in around 1% of clutches.

2012: Three eggs. We always take great note of the markings so that we can keep track of which egg is which.
 
 
Fact 55

Osprey eggs hatch after around 37 days of incubation. However the second egg usually hatches a day earlier at an average of 36 days. A third egg will be a day earlier still at 35 days.

Sometimes the first egg laid is not incubated, or it may be partially incubated, until the second/third is laid. This is an evolutionary strategy ensuring that the whole clutch hatch closer together than the timeframe (usually six days for three eggs) they were laid, giving all the chicks a greater chance of survival.

Fact 56

Osprey chicks typically fledge at between seven and eight weeks old. Males tend to fledge around a day and a bit earlier than females on average.

Celyn and Brenig fledge in 2015
 
Fact 57

Osprey chicks start their first migration anytime from around 80 days to 100 days. The actual age will vary dependent on the strength of the bird, the time in the season and the character of the osprey. Some birds naturally leave early for no apparent reason compared to similarly sized siblings from the same clutch.

Fact 58

Female ospreys are generally larger than male ospreys. A female would typically have a wing span of up to about 6 foot (1.83m) and weigh up to 5 pounds (2.25kg). Males are 10 - 15% smaller which is typical of most raptor species.

Fact 59

Osprey chicks grow rapidly on their pure protein diet of fish. They gain about 30g of bodyweight a day during their first few weeks of life or put another way, they double in size each week for the first five weeks or so. 

Gwynant and Deri in 2014 - food monsters
 
Fact 60

Osprey chicks don't usually fish for themselves until they start their first migration. They are not 'taught' to fish by their parents - don't listen to those old text books!