5 Jun 2018

4 Apr 18 - Atlantic Odyssey - Day Seven: South Georgia - Diving-petrel Quest

During the cruise into the Drygalski Fjord, I spent a lot of time trying to photograph the Diving-petrels. I saw well over a hundred Diving-petrels from the starboard side of the Plancius. As usual, the Diving-petrels were generally not being picked up until they flew off the water & rapidly headed away. Overall, they were very much like Little Auks in their appearance & behaviour. I tried to photograph as many as I could so I could try sorting out the identification afterwards. There wasn't time to look at many of the photos as we were in the fjord as there were so many things to look at.
Drygalski Fjord: The fjord extends seven miles into the island in the South East corner of South Georgia
Quickly checking the photos that evening, I thought I had examples of two South Georgia Diving-petrels. Having spent several hours now peering over the photos, I have now concluded one of those South Georgia Diving-petrels was an out of focus & more distant Common Diving-petrel. The photos of the second were not great, but I think it was a South Georgia Diving-petrel. However, I also looked at some of the other photos & now believe I have found photos of two other South Georgia Diving-petrels. Part of this analysis was trying to get my eye in on Common Diving-petrels & how to identify them. I think it is reasonable to say that in South Georgian waters they are 'perhaps not identifiable in the field'. But I will now qualify that statement to 'perhaps not identifiable in the field with bins for visitors who are not incredibly familiar with the two species'. However, in recent years the quality of modern cameras & camera lenses have improved noticeably & now I think perhaps a reasonable percentage of these Diving-petrels can be identified in the field based upon photos taken & subsequently analysed. Often you need to have a series of photos of the same individual in flight showing them from different angles & trying to identify these Diving-petrels on a single photo is more tricky. The only drawback for Birders is to know which individuals they saw. But if you took the photos, then you would have seen the individuals. So I've put this Post together to see if it helps sort out the identification. I would appreciate any feedback on the identification of these individuals by leaving comments on the Blog.
Common Diving-petrel: While this individual has a white scapular bar (which some Common Diving-petrels can show), it also appears bulkier, longer than the South Georgia Diving-petrel & clearly has feet projecting beyond the tail. The bill appears to be chunky
Common Diving-petrel: Showing the bulk, size & extending feet
Common Diving-petrel: Also, the facial pattern doesn't stand out strongly & is more uniform with the sides of the neck
Common Diving-petrel: Again note the facial pattern, structure & noticeably extending feet
This is another Diving-petrel individual which again the overall features look like a Common Diving-petrel.
Common Diving-petrel: The facial pattern is relatively indistinct, the bill looks stubby & the feet project beyond the tail
Common Diving-petrel: The face & neck pattern look indistinct & it has a dusky underwing
Common Diving-petrel: Again the projecting feet are obvious
I think this Common Diving-petrel is fairly obvious.
Common Diving-petrel: The legs project beyond the tail, the structure looks long & bulky, the facial & neck pattern pattern are indistinct, the underwing is dusky & the bill looks stubby
Another Diving-petrel individual which again I think is fairly obviously a Common Diving-petrel.
Common Diving-petrel: The bill looks bulky, the facial pattern looks indistinct & the feet clearly extend beyond the tail. Some Common Diving-petrels can show white on the scapulars & this looks to be one of those individuals
Common Diving-petrel: The feet clearly extend beyond the tail
Common Diving-petrel: Showing the dusky underwing pattern & the indistinct facial & neck pattern
This Common Diving-petrel looks fairly obvious again, even though I only have one decent photo of it.
Common Diving-petrel: The extending feet & bulky looking bill & indistinct facial pattern looks support this being a Common Diving-petrel
So having got my eye in on what I think Common Diving-petrels looks like, I feeling a bit more confident in identifying South Georgia Diving-petrels.
South Georgia Diving-petrel: This looks like a more compact Diving-petrel with a clear pale collar. The bill looks smaller & more dainty & the feet do not extend beyond the tail. The underwing colouration looks more concolourous
South Georgia Diving-petrel: Close crop of the same photo
South Georgia Diving-petrel: Another shot showing the pale collar, the bill size & shape. Note, the right wing obscures the side of the breast
South Georgia Diving-petrel: Close crop of the same photo
South Georgia Diving-petrel: However, it does show more extensive dark on the sides of the neck that I expected. Again the feet do not extend beyond the tail
South Georgia Diving-petrel: Close crop of the same photo
South Georgia Diving-petrel: In fresh plumage, they would be expected to show white scapulars along with white tips to the secondary coverts. However, this looks to be a worn individual. But the scapular markings aren't a particular good feature as some Common Diving-petrels can show them & worn South Georgia Diving-petrel may not show them. Again the bill shape & lack of foot projection looks good for South Georgia Diving-petrel
South Georgia Diving-petrel: Close crop of the same photo
Here is another South Georgia Diving-petrel.
South Georgia Diving-petrel: This looks to have a more compact body with a pale collar patch, no obvious extending legs, paler underwing primaries & the remains of a scapular bar
South Georgia Diving-petrel: Close crop of the same photo
Finally, this is an interesting individual. The facial & neck pattern & general shape look good for a South Georgia Diving-petrel. Clearly, it has very large feet. However, the tail is very short, so looks like it has lost the tail. I'm really struggling to figure this individual out. But on balance I suspect this is a South Georgia Diving-petrel without much of a tail. [Follow up - I've run this Post past Phil Hansbro regarding identification of these two difficult Diving-petrels. He agrees with the identification of all the above Diving-petrels, but thinks this final tailless Diving-petrel sp. is a Common Diving Petrel. In hindsight, the feet do look very large].
Diving-petrel sp.: This individual has lost its tail so the feet look very big
Diving-petrels are clearly not an easy group to identify & I'm sure there is still a lot more work before their identification is well worked out. Also many photos will end up being left unidentified. Trying to compare these photos to ones on line also needs care to only look at photos taken in South Georgian Waters. There are other populations of Common Diving-petrel & South Georgia Diving-petrel which breed elsewhere in Subantarctic waters. I was told on the Plancius, that there is speculation that the current number of four Diving-petrels. They could be split into a number of additional species, if the same approach of looking at DNA that took place with the North Atlantic Storm-petrels is applied to these different Diving-petrel populations. Finally, I would welcome any feedback on these photos or comments within this Blog Post.

1 comment :

  1. I was keen to get a second opinion on this Post given how tricky South Georgia Diving-petrel can be to separate from Common Diving-petrel. I've had this feedback from Phil Hansbro....

    I have looked at these and think you are right with all of these. I think that the last one is a Common.
    Best
    Phil

    It was really good to get this positive feedback from Phil for the identification & a second opinion on the final mystery Diving-petrel.
    Steve

    ReplyDelete