This year the osprey season has been noteworthy for a number of aggressive intruder incidents on some well known nests (more of that later). At Kielder there have been a few ‘on and off’ landings reported earlier on the blog but on Sunday there was a more sustained intrusion on Nest 2.
Mrs 37 had been relaxed on the eggs when she spotted an osprey in the sky and started mantling. An intruder’s legs hovered over the nest and the bird, thought to be female, landed on the right hand edge after a few seconds.
Surprisingly Mrs 37 left the nest almost immediately. A successful breeding female will normally defend the nest, particularly against another female, and risk physical harm. But Mrs 37 responded to the self-preservation instinct. 37 was notable by his absence – probably out hunting a couple or more miles away as the rain had just lessened – so did being alone push her towards self-preservation rather than nest protection?
The intruder took advantage and hopped onto the empty nest, looking round frequently and appearing unsure how to behave. But over the next 16 minutes only the intruder was on the nest and the eggs were kicked or trampled several times.
Eventually the intruder left and Mrs 37 landed immediately and incubated. She was still alarm calling for a time but settled on the eggs and soon afterwards 37 returned. During the afternoon there were two more intrusions by an unseen bird; on the first 37 joined Mrs 37 briefly before chasing after the bird.
On the second occasion he landed and Mrs 37 went off after the intruder whilst 37 incubated.
Careful examination of the eggs by a number of pairs of eyes did not reveal signs of damage, although there is no optical zoom to provide a better view.
Today the intruder (presumably) was around once more and the eggs, still looking undamaged, were left exposed on a cool and breezy day for over two hours whilst Mrs 37 initially, then 37 (back with a fish), defended the nest with only very brief landings. This exposure poses some degree of risk to their viability at their stage of development. But either 37 or Mrs 37 has been covering the eggs since late morning until the time of writing, 15.00. Let’s hope the intruder has got the message and all ends well at hatching time, the end of the month.
As mentioned earlier, other nests have experienced even more aggression. At both Rutland Site B and Loch Garten persistent harassment by several male intruders prevented the resident males from supplying fish to the females and in both cases clutches were lost. Thankfully the breeding males were able to regain control of their nests and a second clutch was laid at Site B. As the population increases successful nests are an attraction to non-breeding ospreys and these intrusions reflect successful population growth.
Here is a video of some of the intrusion yesterday.
Especial thanks to Emyr Evans of the Dyfi Osprey Project for taking the time to check the video footage. Many thanks also to Paul for his input.