Intruding Ospreys at Dyfi

2020 Intruders - 12 in all, a new record

(5th column refers to age when seen)

Intruder Ospreys

When an osprey encroaches on the Dyfi nest that is not usually part of the Dyfi family, we get very excited!


LOOK OUT!! An intruder approaches Monty and Nora's nest in 2012 - ring number Blue 12. We would see this bird again...


Active nests act like huge magnets to other ospreys, especially singletons - those birds that do not have a mate or a nest of their own. Ospreys prefer to inherit or displace another bird for its nest rather than having to build one from scratch. There's a good reason for this too - if they come across a successful nest, it must mean that it is in a good location with plenty of food; someone else has made the nest location decision and got it right, so why bother risking it yourself?

We get dozens of 'Intruding ospreys' every year, the trick is trying to identify them. The best clue to an approaching intruder is not by eyesight, it's by the reaction of the Dyfi ospreys themselves. Their eyesight is much better than ours and they can spot an intruder literally miles away. They are our alarm system for the guys in the 360 Observatory to look up and for the camera operator in the office to (Ed: start panicking) get ready to start searching the skies!


Have a look at this video - this is the typical response that we look out for when another osprey encroaches into the Dyfi osprey air-space:

The osprey in the video is Glesni and that frantic wing flapping behaviour is called 'mantling'. The rapid alarm calling we call 'chipping' and ospreys only 'chip' at other ospreys, no other species, so we always know there is an intruder osprey about when we hear these chips (we could have put a fish & chip joke in here but we are far too professional for that).

Between 40 - 50% of British ospreys are ringed, so at least half of the intruders we will never manage to identify. Of the remaining ringed birds, only a handful venture close enough to the nest for us to be able to make a positive ID - they really need to perch somewhere; something that most intruders are not happy doing with two other ospreys going berserk at them!

So here is the list of ringed birds that have 100% positively been identified as intruding the Dyfi nest since 2011. Every autumn we'll add the current season's intruders to the list:

Here are some interesting facts we've learned from these intruding ospreys:

       1. Around 80% of the intruders are female. These are no doubt birds looking for a male holding a nest and territory. Most just pass on through quietly, while others will make more of a fight for the nest - like Blue 24 for example.


Blue 24 dive bombing Brening, a 2015 male youngster


   2. All of them are young birds, around three years old on average. This again tells us that these are non-paired up ospreys trying to breed and settle down for the first time.

Glesni (left) is surprised to find a two-year-old Scottish female just popped onto her nest - not happy!


 3. Around half the intruders are English birds, but there are two Welsh birds there, both Glaslyn ospreys: White YC (2008) seen as a three year old in 2011 - he successfully raised chicks in Cumbria in 2014, but failed at the same nest in 2015 due to disturbance. The other is Blue 80(2012) spotted at the Dyfi nest as a two-year-old adult in 2014 looking for nest sites. He returned again to the Glaslyn nest in 2015 where he paired up with his mother for around a week before he was displaced by another male who subsequently successfully bred at the nest, producing two chicks in 2015 (unringed osprey named 'Aran").

Blue 80 being ringed in the Glaslyn as a chick in 2012 and near the Dyfi nest as a two-year-old adult in 2014 looking for nest sites.


       4. Blue CU2 was a Scottish two-year-old male spotted in August 2014; we nicknames him Jimmy!. He returned to Wales in 2015 looking for a nest site and looked as if he was going to pair up with the Glaslyn female for a few days before moving on.
He didn't go far, he was regularly seen around Llyn (lake) Brenig just 25 miles to the east possibly building his own nest. Sadly, Jimmy was found electrocuted a few weeks later on 11th May 2015 near the village of Pentrefoelas, just to the west of Llyn Brenig.




The Dyfi ospreys regularly use electricity poles to perch on, especially Blue 24 and Monty.



Blue 24


Following on from Jimmy's sad demise, we are greatly indebted to Scottish Power who helped us put anti-perching devices on all the electricity poles where the Dyfi ospreys perch. 


Intruder Videos

Each year we try and identify as many of the intruding ospreys as possible. Follow the links below to the videos of each years visitors:






Of the 100 or so 'intruder events' we record each year however, only a handful of ospreys are positively identified, most go about their way and we have no idea who they are.

Finally, here's an interesting one...

4th June 2015: Everything seems normal, all the Dyfi birds are present, but we have one too many! Who is it?

Down you come son...