Saturday, 28 February 2015

Infamous Grouse

The Famous Oslo Grouse has proven quite popular with birders and it has been suggested that it is an even more exceptional record than I first thought.

When I saw the bird I did not consider that it was anything other than a Willow Grouse (lirype). Ptarmigan (fjellrype) looks pretty much identical in white winter plumage but the chance of this bird being that species did not warrant any thought, or so I thought. After all the habitat did not suit the high montane Ptarmigan and of the two species Ptarmigan is hardly ever seen seen away from its breeding sites whereas Willow Grouse is known to wander. It has however been pointed out that the bill of the Oslo bird is very small and in white winter plumage that is one of the few clues to separate these two species whose white plumage is identical. Male Ptarmigan has black lores (the area between the bill and eye) but female Ptarmigan and both sexes of Willow Grouse have white lores. The Oslo bird has white lores so this rules out male Ptarmigan but not female. Otherwise, Ptarmigan is a slightly smaller bird but size is notoriously difficult to judge on lone birds. The calls of the two species are slightly different but I have not heard it call and the one observer who has heard it heard a call unfamiliar to him for either species!

There is one other difference which is the colour of the claws. BWP describes the colour as blue-black for Ptarmigan and horn-brown for Willow Grouse. I have not found many photos on the web to confirm this although have not found anything to suggest this colour description is wrong. The colour of the Oslo birds claws are difficult to see due to a lot of feathering but this picture by Per Buertange shows them to be horn-brown. It has also been stated (this was a statement by one person which has not yet been supported by others) that exactly the excess feathering is a Willow Grouse character.

Bill size can be easily checked on photos on the web and it is clear that there is a huge amount of individual variation between the species with some Ptarmigan having in my eyes monster bills whereas some Willow Grouse (females?) have small bills that match the Oslo bird. I also took a picture on 12 Feb of a Willow Grouse in Hedmark that matches the Oslo bird. This bird was in a lowland, forest habitat with a flock of similar birds so is for me undoubtedly a Willow Grouse. Also BWP confirms the large individual variation with the following measurements being given:

                                    male                female

Ptarmigan                  9.0 - 10.6          8.2 - 9.8
Willow Grouse        10.0 - 12.8          9.8 - 12.3

So what do I think the bird is? Well I find the thought of it being a Ptarmigan so outrageous that I still believe it to be a small-billed female Willow Grouse which the claw colour supports. Here is a picture showing the bill of the Oslo bird (right) with a comparison to the bird I photographed in Hedmark. If the claw colour (and feathering of the claws) are not diagnostic then it is difficult to know how to 100% prove the ID of this bird. Trapping it to take measurements would be ethically wrong but it is probably possible to take DNA from its droppings.


  1. In my opinion, the Hedmark and Oslo birds in your comparison illustration are very different in regards to bill proportions. Like two different species, I would say. :-) And why would it be ethically wrong to capture and release the bird to measure it? After all, both species can be hunted in Norway at this time of year.

  2. Hi Bjørn, I agree that the two birds bills are not the same but for me it does illustrate that Willow Grouse can have a much smaller bill than the literature will have us believe. That being said though I think that if the Oslo bird had been pictured from any other location then I would not have questioned it being a Ptarmigan. I just find it so hard to believe that a Ptarmigan would be inside a wood at (almost) sea level a long way from its normal range. Probability says it is a Willow Grouse. It is also clear that we as birders have very little knowledge of these two species in white winter plumage - I'm certainly having to base my comments on literature and feel very unqualified on this subject.

    Regarding ethics, then you know through our many discussions that I am against trapping and ringing of birds that does not have a clear and worthwhile scientific objective. To trap a bird just to satisfy the needs of some frustrated and curious birders does not for me warrant the stress of trapping this bird which may well be weak and under nourished judging by its behaviour. The fact that they can be hunted is of course unfortunate but two wrongs do not make a right.

  3. Science has always been driven by frustration and personal curiosity - and always will be. In this case, certain identification using biometrics might teach us a lot about either the variability of Willow Grouse or the behaviour and winter habitat selection of Ptarmigans. If this mystery remains unsolved, no new knowledge about either has been gained from this very rare opportunity. To me, not doing all that can be done in order to gain more knowledge about birds, without deliberately breaking the law or harming the birds (careful handling a few minutes is seldom harmfull to them), is even less ethical.

  4. We gain absolutely no new useful knowledge from capturing a single bird outside of its normal range (for all we know it has been brought here and released by one of our species). If there is a need to know more about biometrics of grouse then someone can look at the thousands that are (most unfortunately) shot each year in their natural habitat. DNA from its droppings will tell us all that we curious humans need to know about this bird and it will be not impact the welfare of the bird at all.

  5. Well it looks like I did overlook one other method of proving ID: use of playback. Bjørn Olav played both Willow Grouse and Ptarmigan calls (song?) to the bird today and its response left little doubt as to which species it was: Ptarmigan!! So despite me not thinking it possible it now seems that all evidence does point to it being a Ptarmigan (Bjørn Olav also having found pictures of Ptarmigan with claw colours matching this bird).