Will we be invaded?

Most, but definitely not all, winters see the arrival of a scarce irruptive species (or two or three) in the Oslo area. The classic species are Pine Grosbeak, Two-barred Crossbill, Hawk Owl and new to the list Great Grey Owl.

We currently have a good berry crop especially on planted asal trees in urban areas such that we can hope that if Grozzas do irrupt this autumn then we at least have food for them.

berry laded trees on this morning's dog walk. I can never remember quite so many berries on these exact trees

We had none last winter but proper invasion winters in 2024/5, 2021/2022, 2019/2020, small numbers 2017/2018 and 2016/2017 and good numbers in 2012/2013 when there were no berries but they fed on fresh shoots in spruce trees.  Two-barred Crossbill is far less regular but we had good numbers in the winter of 2019/2020 which was a good crossbill winter in general due to a lots of cones but should they also arrive when there are not cones then they may find other food such as in the winters of 2014/15 and 2013/2014 when small flocks fed on some ornamental seed stones in the Oslo Botanical Gardens.

Owls irrupt following good breeding seasons which means there are a lot of owls and then a collapse in rodent populations means little food and causes the owls to spread out looking for places where there is food. Hawk Owl has long been a species that can turn up around Oslo and does so pretty much every 4 years with a bird two winters ago in Maridalen and multiple birds in the winters of 2020/21 and also 2019/20, 2016/2017 and 2012/13. It is therefore not to be expected that we have a bird this winter but of course not impossible. Great Grey Owl is so new as a breeding species in southern Scandinavia that we have no history with which to make predictions and it is only the winter of 2019/20 that we have previously had the pleasure of their company in Oslo. However, it is clear that they irrupt in the same way as Hawk Owl with good breeding seasons followed by rodent population crashes causing them to wander.

Great Grey Owls had a very good breeding season in their core area last year which I was able to enjoy but less successful this year as rodent numbers had already started to decline. Rodent should now be hitting the bottom of their 3 to 4 year cycle meaning there are good numbers of owls needing to find food. There have already been reports from the coast suggesting birds are on the move so my hope has, for quite a while, been that this winter will again host GGO in Oslo. We also have lots of new clearings due to extensive forestry work and these provide ample (perhaps too ample for the birder wishing to find one) hunting grounds for the owls. The only remaining blocks that have to fall in place are for there to be enough rodents around Oslo to sustain an owl or two during the winter and for the owls to find them and decide to stay.

There have been no signs that this summer has been good for rodents with Tawny Owls being unusually hard to hear in Maridalen but intriguingly there have been a small handful of reports of Great Grey Owl from the Maridalen and Lillomarka area since last November. Some of these were third or fourth hand reports that were difficult to know what to make of but there have been some photographed birds. I am certain that there has not been breeding but rather wandering young bird(s) from last summer’s good breeding season further north have made it to the Oslo area and are scratching a living.

A report of a bird on Sunday with photographs clearly taken with a mobile phone of a bird hunting in the day in Lillomarka was interesting and exciting. Was it the same bird that had been reported those handful of times or was is a new wandering bird and the vanguard of the invasion I have hoped for? We can of course not know for sure but developments through the late autumn will give us a clue.

I of course went looking for it yesterday morning and for once took the Beast with me as a long and potentially unrewarding walk in the woods would be made more enjoyable with some company and as he now approaches late middle age he has become a bit easier to take birding. Also, he would hopefully be a lucky charm as his breed name Finnish Lapphund shares the same Lapp name as Great Grey Owl in Norwegian (lappugle). A bit convoluted I know but I will take all the help I can get.

We didn’t find it in our first check of the area where it had been seen the day before and continued through the forest checking out where Honey Buzzards had bred this year in a new nest but which I had not previously visited due to my far more accessible nest in Maridalen. Coming back a couple of hours later though there it was perched very openly on a tree stump just as they are supposed to do. There then followed nearly three hours of observation when I watched it make four succesful catches all of which it ate on the ground so I could not see exactly what it caught but once did see a long tail sticking out as it swallowed the prey. After the first three catches it resumed hunting immediately and it was only after the fourth that it seemed sated enough to relax and preen. It had clearly found an area with, for the moment at least, good numbers although the fact it is hunting so much during the day in such an open area does suggest that the bird is both very hungry and that there are not many rodents as otherwise it would hunt within the forest as night.

It will be interesting to see how long it stays but I doubt the one small area where it was can have enough food to sustain it for too long so it will surely soon move on although maybe not far.

I continued my long track record of failing to press record when I thought I had so do not have digital memories of some of the scenes I witnessed but have managed to capture some hunt and flight sequences.

Great Grey Owl (lappugle)

much too low shutter speed but I don't think anyone would expect anything else of me :-)

well camouflaged in black and white

it very clearly has two generations of primary and secondary feathers which I interpret as meaning it is a bird born last year with a mix of juvenile and adult feathers

some pics from the phone including an obligatory selfie

lapphund og lappugle

Egrets

The second half of the week has, unsurprisingly, not been able to measure up to the good start but it has offered some good autumn birding. A trip to Nordre Øyeren today in damp conditions revealed a Svellet completely free of waders despite there being lots of attractive (at least to me) mud still showing. There were three Great White Egrets close by though and this is now a characteristic species for the area in the autumns. Despite it now being expected it is still a bit of kick to set your eyes on them and they are still exotic.

Bird of today was a calling Red-throated Pipit (lappiplerke) that flew right over my head when I was looking over Snekkervika but it wouldn't stop unfortunately. Also still there were two Red-backed Shrikes (tornskate) which are getting to be quite late.

Great White Egrets (egretthegre) - the bird on the right is perhaps an adult with what look like plume feathers sticking out

This video shows a dark juvenile Honey Buzzard and an adult Common Buzzard in Maridalen on Wednesday and continue the great run of sightings I have had this autumn

a video grab of the dark juv HB

and a picture of the pale juv HB that isn't in the video

the dark juv HB with a moulting (adult or at least 2cy+) CB

In this video of a Black-throated Diver family on Maridalsvannet from Thursday the youngster can be seen being fed small fish

juvenile Black-throated Diver (storlom)

BtD family

Goosanders (laksand)

a record breaking flock of 32 Cormorants (storskarv) that flew into Maridalsvannet yesterday and immediately set about feeding (or at least searching for fish) as a flock as can be seen in the video

Shoveler (skjeand) including an adult male in eclipse which I don't remember having seen in Norway before and a pair of Gadwall (snadderand) at Merkja today

A Nutcracker (nøttekråke) collecting hazel nuts in the garden on Wednesday. They do not eat them but rather fill up their throats/crops and fly many kilometers into the forest with them where they hide them to be eaten during the winter. In the video you can see it taking nuts and also see the bulges in its throat

This mink in Maridalen did not seem to have seen me and The Beast sitting only meters away but as can be seen could definitely smell us

Pallid time

I have had a couple of very enjoyable and of course successful guiding trips recently. Both were morning outings with the delights of Maridalen featuring in the first trip and the second which entailed a pick up in Lillestrøm worked well to put the spotlight on Årnestangen and Nordre Øyeren. For the Årnestangen trip I was booked as a birthday present from a clearly very loving and thoughtful wife in Panama for her husband who was in Norway on business!

We were at Årnestangen on Sunday morning and there were far more birders there than usual with a Pectoral Sandpiper seen the previous day probably being the draw. The Pec was not refound but it turned out to be a good raptor day. Ryan and I had Hen Harrier, Peregrine, Merlin and White-tailed Eagle among others but after we had left a juvenile Pallid Harrier was seen.

Pallid Harrier is a species I cannot get enough of. When I was a teenager it did not even feature in the bird books I had but has in the last couple of decades clearly expanded westwards. The reasons are not clear but changes in farming practices in the former Soviet republics are a possible cause with birds having to look for new breeding sites as old ones become unsuitable.

I have been lucky enough to find three birds myself but none have been exactly good views. I have twitched a couple of males that spent thesummer one year near Valdresflya and that was a great though damp and grey experience. For a long time I was missing a good, prolonged and close meeting with a juvenile bird though but that came to fruition in 2022 with another twitch but only half an hour from home.

Every autumn I visit places such as Nordre Øyeren with the plan of finding a Pallid Harrier but am always disappointed. Yesterday when I decided on another trip to Årnestangen I had the same hope but nevertheless expected to be disappointed. It was a damp start to the day and definitely not classic raptor conditions but there were raptors. First a Marsh Harrier then a Hobby, then the Marsh Harrier again and as I tried to get the scope on it another raptor appeared and it was a juv Pallid Harrier! I assumed it was the same bird as two days previously but later experiences make it clear to me that it could very well have been a new bird (and there seems to be quite a few birds moving through southern Norway in these days). With only the superzoom my digital memories of this fairly close encounter are of course not that great but hey I enjoyed it!

 

juvenile Pallid Harrier (stepphauk)

just as striking from above

The raptors were far from over in their generous giving though. As I retreated in my steps to try to refind the harrier which had disappeared behind some bushes I looked up and saw an immature White-tailed Eagle chasing a Peregrine. The falcon, an adult, had a wader, probably a Ruff, in its talons and was trying to gain height and fly away from the eagle but the eagle kept catching up and following the falcons every move. The falcon then dropped its prey and the eagle stooped down and caught it mid-air!! I was certain that the Peregrine could out manoeuvre the eagle but maybe the prey was just too large and heavy for it. Impressive flying by the eagle though and something I wish I could have recorded digitally although I was so enthralled watching it that I didn’t even consider lifting the camera. When this was over I then saw that the Pallid Harrier was flying over where I had first seen it and I then hurried back there and out to the end of the peninsula. I chose to watch from the old tower as I thought the elevated position might prove advantageous and it did. I picked up a female Hen Harrier working her way towards me and then she put up the Pallid which must have been resting unseen in the grass! The two flew together for a bit and then disappeared from view. I waited a god while hoping they would reappear but in vain. I then hurried out to the end of the peninsula and as I did so the Pallid flew quickly past and then in true Top Gun style did a fly-by of the tower where I had just been standing!!!

 

3 of 5 White-tailed Eagles (havørn)

female Hen Harrier (myrhauk)

I then spent around three hours on the platform at the tip and have to say I was pretty happy with my time there. There were quite a few waders including my first Grey Plover of the year I twice heard a call that matched the recording of Pec Sand that I had on my phone but never saw the bird that gave it although there were clearly many waders that were very hidden as a couple of Lapwing only gave themselves away after I had been there a couple of hours when a Kestrel caused them to call and then briefly fly up from behind a long line of willow bushes. Many of the waders present match what was seen on Saturday to it wouldn’t be a complete surprise if the Pec Sand was also present but well hidden.

Bird, if not sighting, of the day was a 2^nd winter Mediterranean Gull which I picked up resting with Herring and LBb Gulls before it quickly flew off. This was a species that up until a few years ago was becoming almost expected but has since become rare again.

There were also a couple of Great White Egret, a migrating juvenile Honey Buzzard (I have never seen so many as this year which must be proof of a great breeding season) and then another sighting of a juvenile Pallid Harrier. It was suddenly in the air with a Hooded Crow harassing it and then landed for a few minutes and giving good scope views before then flying off south-west over the water and then thermalling over the “mainland” before disappearing. This bird had a different jizz and did not appear to be quite so long and thin winged as the earlier bird making me sure I had seen two different birds.

 

this is the second Pallid when it briefly rested before crossing the water to the SW

and this video has the first Pallid, the female Hen Harrier, both harriers flying together and then the second Pallid together with a Hooded Crow both in flight and on the ground

Here is my eBird checklist for the day, a day I reckon will be hard to beat this autumn, or at least until I go to Værøy in three weeks 😊

this Black Woodpecker (svartspett) was in a the final bunch of trees at the end of the peninsula and on three occasion flew out heading south (and otherefore over the water) before each time returning. If 3km of water is too far then it is no surprise they have never been seen in GB

a latish Red-backed Shrike (tornskate)

and another

here we see one of them is carrying a ring

and a picture from Maridalen of a migrating juvenile Honey Buzzard (vepsevåk). I know the bird is completely unidentifiable in this picture but you can at least see it is in Maridalen

and three Common Buzzard (musvåk) in a tree

Raptor time

The Oslo Honey Buzzard nest that I have been following this summer is now empty (as far as I can see) although if you have been following the Sussex Honey Buzzard nest webcam on YouTube then you will know that the young can potentially still visit the nest four weeks after taking their first flight so my lack of sightings is definitely not absolute proof that they are gone. I will of course have a loooong but hopefully interesting post on the nest later in the autumn.

At the same time I no longer found any HB at the nest site I was following (I also know of another successful nest in Oslo this year) I noticed multiple juvenile HB over Maridalen with some birds definitely migrating in a southerly direction (both south east and south west) and other birds seemingly just enjoying thermalling, soaring and landing in the woods where I would love to to know what they were doing. It therefore seems clear that the species has had a good, and early, breeding season in southern Norway in 2026.

All the time looking at the sky has resulted in quite a few other raptors with seven species in Maridalen and a session at Årnestangen yesterday giving ten and I have seen 12 in total this last week. Nothing too exciting yet but juvenile HB in a direct flight have a very harrier like jizz and many birds also have narrow pale rumps so I have been eft scratching my head quite a few times.

Årnestangen yesterday was apart from the raptors a very strange affair with the extensive mud/sand flats almost completely empty of waders with just two Dunlin and two Greenshank. Svellet though has been far more productive with large numbers of both waders and dabbling ducks. A Broad-billed Sandpiper here was the undoubted highlight and a species I had forgotten about completely when in my last post I moaned about the wader species I had yet to see this year.

Great White Egrets have now turned en masse at Nordre Øyeren with 12 being the highest, and a record, count. I have had to content myself with just eight including a flock of six.

a migrating juvenil Honey Buzzard (vepsevåk) which is a grab from this video

the pale Common Buzzard (musvåk) in Maridalen. It has been around a few years now but for such a distinctive bird I see it quite infrequently.

my first Great Grey Shrike (varsler) of the autumn on the early date of 31 August. a lack of a wing bar shows it to be an adult and the all black bill probably a male

six Great White Egrets (egretthegre) and some Cranes (trane) at Svellet

and two at long range at Årnestangen

a video of a male Hen Harrier (myrhauk) at Årnestangen:

and a Marsh Harrier (sivhauk) eating a young gull at Svellet: