Breeding Red-throated Divers

One of the reasons for infrequent blogging over the summer was that a lot of my time was spent observing scarce breeders. There were four species I was lucky enough to follow and in addition to all being rare/scarce around Oslo they had all chosen to nest surprisingly close to humans.

The species were Great Grey Owl, Honey Buzzard, Red-throated Diver and Goshawk.

Goshawk is a regular breeder in Maridalen but the nest that I spent time with this summer was special due to it being passed by hundreds, if not thousands, of people every day but seemingly without anyone noticing.

Great Grey Owl is always an exciting bird and I was lucky enough to be shown two nests both of which were on broken off tree stumps (in itself a very rare occurrence in Norway) and also both very close to roads.

The Red-throated Divers chose to nest on a lake popular with bathers and nightime partying youth and the Honey Buzzards were in the forest but surprisingly close to the city and nesting right over a path.

I was lucky enough to be told about three of the four species so thank you to my informants but I will not mention your names so as to try to maintain some secrecy.

 

I will start first with a post on the divers.

 

I visited the Red-throated Divers first on 14 June when an adult was sitting on the nest. I visited fairly regularly without there being particularly much to see until 12 July when the first youngster had hatched and then the next day there were two. This means the breeding was quite late although given the location the incubation period may have been very extended as apparently they can use up to 2 weeks longer than normal if they are disturbed. By July 28 both adults were leaving the breeding lake to collect fish. On 3 September only one youngster was left on the lake with an adult in attendance and on 5 September the breeding lake was free of birds but I noted an adult and juv together on Maridalsvannet that can reasonably be assumed to the birds I saw on the 3^rd.

The lake they chose to breed on was not just surprising given the level of human disturbance the birds were subject to but it was also a lake which had lots of small fish in and Cormorants for example fished there. I have always understood that Red-throated Divers breed on small fish-free lakes and fly often long distances to other lakes to fish (this is different to Black-throated Divers which breed on large lakes where they also fish). I have never understood why Red-throated Divers would choose to do this but I was very surprised to see that the adults continued to fly to other lakes to feed and collect food for the young when there were clearly lots of small fish in the lake they were nesting on (I both saw fish and the presence of the Cormorants).

The late breeding with egg laying having to occurred in June is also interesting as birds were back on Maridalsvannet at the end of April. The birds that gather and display on Maridalsvannet breed on small lakes in the surrounding forests and will have included this breeding pair. Their late breeding suggests to me that a first breeding attempt (either on the same lake or somewhere else) failed and that they tried again. The first indication of Red-throated Diver breeding in (or at least very close to) Oslo came as recently as 2014 with birds on Maridalsvannet in July but the numbers of displaying birds on Maridalsvannet this spring can suggest that as many as 3 pairs may be breeding now. The adult birds fly to and from the lake in various directions and often make a lot of noise in flight but their breeding lakes have to my knowledge not been discovered previously.

These birds were hard to avoid though as the adults often made a LOT of noise and non-birding users of the lake often asked me about the birds. It is therefore surprising that they did not become more widely known about with just a couple of photographers seemingly becoming aware of them.

I took rather a lot of video and pictures on my visits and it has been especially time consuming going through the videos but I present 5 videos from different dates that show the progress from nest to nearly fledged young. Some of them are long especially that from 13 July (1-2 day old young) but they are worth looking at in their entirety as there are some little gems of behaviour.

14 June - my first encounter with the birds

15 June

6 July - a hot day

15 July

adult arriving with food

the fish is cleary too large for this 1-2 day old youngster

off to Maridalsvannet to hopefully catch something smaller

one of the young peeking out from a protective wing and pecking at some vegetation

28 July

much bigger

4 August

an adult after having caught a fish at one of the fishing lakes

on its way to the nesting lake

the adults would often greet and call to each other

6 August

still very downy

when the young want food they peck at the neck of the adult

19 August

looking more adult like but still some downy feathers

the two youngsters were on their own on the lake and were practising diving and coming up with bits of vegetation

an adult arrives with a fish

the one that didn't get food quickly starts begging

and doesn't stop

3 September

just one youngster left on the lake. The two young hatched a day apart and one was always a bit larger than the other

not much difference in size and two days later they were gone