Our established pair of #FoulshawOspreys, Blue 35 and White YW, has successfully raised youngsters at Foulshaw Moss for ten years. 

In this, their eleventh year, they became parents again when three little down, covered osprey chicks came into the world on 18, 19 and 22 May.

During the incubation weeks, just one or two fish deliveries a day were adequate to keep mum well fed. 

Since hatching, the pair must now use all their energy to feed the chicks so that they grow into full sized young ospreys ready to the leave the nest in just a few weeks. 

They will likely fledge between seven and eight weeks after hatching and set off on their migration south in late August or early September.

So there is a lot of feeding to be done. Catching the fish for the family is the responsibility of dad (White YW) while feeding the chicks is generally down to mum (Blue 35), although dad has had a go .... when allowed.

Fishing -  what do ospreys eat?

The nest isn’t far from water so dad has plenty of choice for fishing fairly close to home. He will hunt for freshwater or marine fish and doesn’t seem to have a preference. 

In general, ospreys are opportunists and concentrate on catching fish that are most available, regardless of their species. They will catch any size of fish from 50 grams to near their own body weight of 2 kg. 

Experienced ospreys, like YW, are more likely to use their energy hunting for larger prey. This fish looks pretty big.

Not all forages are successful but experienced ospreys will have perfected their fishing skills over the years and a bird such as YW is more than likely to catch their prey 70% to 90% of the time. 

Ospreys’ bodies have adapted for catching and eating fish and we’ll have a look at “osprey morphology” in a later blog.

Foraging

How does YW decide when and where he will fish? Will he venture up the river Kent, explore the estuary at Arnside, find a well stocked lake or go out to sea at Morecambe Bay? He has to take into consideration the weather, the tides and fish movement. 

Unlike seabirds which can dive deep head first into the water, he's a shallow fisherman and can only catch fish that are close to the surface: normally no deeper than one metre. 

He may be looking for surface swimming fish in deeper water or fish that hug the bottom in shallower water. If it’s stormy, the water surface will be choppy obscuring the fish, making it more difficult for him to see his prey. 

Does he wait until the tide turns when there are more fish around? So he has a lot to consider before going hunting: meanwhile on the nest there are hungry chicks waiting to be fed and a mate shouting at him for a meal. 

The Catch

Watching the spectacle of an osprey fishing is an amazing experience. It will fly back and forth hunting for prey, hovering, flying, hovering again until it spies its target. 

Then it plunges down towards the water, legs and talons reaching forward in front of its head, wings tucked back. It thrusts its legs into the water, grabs the fish with its talons, and then heaves into the sky with strong beats of its water soaked wings and body. 

A quick shake and a turn of the fish to face the front and it flies off back to the nest.

Case study of osprey feeding times and fish deliveries

For seven days from 29 May the nest was carefully monitored to find out how many and what kind of fish YW brings to the family and how many mealtimes the chicks had. At the start of the survey, the chicks were 11 days, 10 days and 7 days old.

Over the course of the week, YW delivered twenty fish to the nest: 10 flounder, 9 trout and one teeny roach. So the average fish delivery during this time was just under 3 a day!

Flounder and trout are definitely favourite but other fish that have been seen outside of the study period are the occasional mullet, pike and salmon. 

There is quite a bit of detail in the chart which helps to paint a picture of life on the nest and how mum and dad work so well together to make sure their chicks are well fed. 

The times of the fish deliveries are shown when mum feeds the youngsters. If dad brings in a large fish it normally lasts through several mealtimes and sometimes overnight as well. Often the fish is left on the nest after feeding so that mum can feed again when the chicks wake from their food coma.

At other times dad flies in when mealtime has finished and takes the fish remains away to enjoy on the roost tree. He either finishes the fish or brings the remains back onto the nest for the next mealtime. 

Mum snatches mouthfuls of fish whenever she can and often finishes off the fish remains: skin, bones and spines. She probably is the least well fed during this time and will have plenty of opportunity to rebuild her strength once the chicks have fledged.

There were a total of forty-nine mealtimes across the week giving an average of 7 a day. The earliest breakfast was just after 4 am at daybreak: most breakfast times were close to 7 am with one a little later at 8.40 am. Supper times ranged between 7 pm and 9 pm. 

As the days are long there are plenty of daylight hours for dad to go fishing. In reality, he does seem to spend a considerable amount of time on the roosting tree: something we can see this year on the new roost camera!

On day 1, it was raining heavily when dad delivered breakfast at 8.40 am. Mum decided not to move from protecting the chicks until the rain eased at 10 am, when they had their first meal of the day. 

Day 2 started with plenty of fish remains on the nest which lasted until dad caught a generous sized fish at 11.14 am which kept the family fed until the supper meal just after 8 pm. 

On day 6 and day 7 there were large gaps between fish delivery times. This wasn’t caused by bad weather but pestering crows about on one day and intruders the next, which kept dad busy and attentive protecting the nest rather than going fishing.

If you watch the live stream you'll have noticed that some fish come to the nest intact and very much alive whilst others arrive without their heads after YW has had a feed. The reasons for the difference aren’t totally apparent.

It might be that YW is very hungry and can’t wait for his turn; or maybe the head is the tastiest part of the fish that he feeds on first or perhaps eating the head immobilises the fish which helps avoid flapping accidents in the nest.

If dad delivers straight to the nest, he may be aware of how hungry the chicks and B35 are. Of the fish delivered during the week, 4 flounder and 3 trout were delivered without heads.

Our #FoulshawOspreys parents have successfully raised twenty nine ospreys already and they continue to be attentive, working hard to make sure their family is well fed. 

My thanks to each one of the knowledgeable Foulshaw osprey volunteers for their help with this blog. If you are able to make a visit to Foulshaw Moss, they will be on hand to make it more interesting, fun and informative.