Shearwaters off Ngor, 15/04
First of all let me apologise for the stream of mostly blurred pictures that is about to follow. I’m pretty pleased with the picture above, but found it really difficult to get decent shots of moving birds from a moving boat, one hand on the camera and the other holding on to the boat… and this despite the fact that the ocean was really quite calm when we set out on a mini-pelagic last weekend.
We didn’t see a huge variety of birds but what lacked in diversity was made up for by the quality of our encounters and by the good numbers of shearwaters – mostly Cape Verde but also quite a few Scopoli’s Shearwaters and probably some Cory’s too. Three species of Skuas (Long-tailed, Arctic, Pomarine) were seen, but only a few Northern Gannets are left, while four storm petrels were seen too briefly to be sure (probably Wilson’s). Other than that a single Audouin’s Gull, two migrating Black Terns and of course Royal and Sandwich Terns, albeit in small numbers. Oh and a lone Barn Swallow migrating low over the waves. In 2015, a similar boat trip on almost exactly the same date (18/4) produced quite a few more storm petrels (European, Wilson’s, Madeiran), two additional shearwater species (Manx and Sooty) as well as several Sabine’s Gulls.
I should really go out more on these boat trips as there’s always something interesting to see, and it really is a unique experience to find oneself surrounded by seabirds feeding around you. Last week’s trip is also a good opportunity to review some of the ID challenges with our Calonectris shearwaters, so here we go:
Cape Verde Shearwater Calonectris edwardsii
By far the most numerous bird of the trip, with at least 200 birds spread mostly between two groups. When seen at close range this is also one of the easier ones to identify: a medium-sized shearwater superficially similar to Cory’s/Scopoli’s, but clearly smaller and more slender, with a longer tail and overall plumage being more uniform brown and darker above. Its bill is rather fine, mostly grey without any yellow tones; some may even appear almost pinkish (see 3rd picture down).
The upperparts aren’t as contrasted and largely lack obvious grey in the wings and back compared to Cory’s/Scopoli’s, and do not display a distinctive dark “M” (or W, depending how you see things!) across the wings as on Scopoli’s, only a slightly darker band across the arm:
Under strong light they do sometimes look paler and may show a slightly mottled back:
Especially on swimming birds, the dark head can be fairly distinctive and may even be reminiscent of Great Shearwater. The size difference with Cory’s is striking when seeing the two species together but of course this is much harder when watching these birds from land while they are feeding out at sea or flying a kilometer away from the shore. The Cory’s Shearwater in the picture below (yellow bill with dark tip, pale grey head) looks huge compared to the Cape Verdes, which suggest Cory’s rather than Scopoli’s – but see further down for a discussion on separation of these two closely related (sub-)species.
Cape Verde’s underwing pattern is intermediate between Cory’s and Scopoli’s Shearwaters, usually showing a sharp demarcation between the dark primaries and underwing coverts. The paler inner webs on the primaries make the hand look more grey than black, though this is visible only under good light conditions and is less distinctive than on Scopoli’s.
Cape Verde Shearwater considered a globally threatened species, under the category Near Threatened on the IUCN Red List, owing to its moderately small population and range size. There are said to be around 10,000 breeding pairs (= ca. 30,000 birds in total), largely limited to just three islands of the Cape Verde archipelago. The population is thought to be declining owing mainly to uncontrolled levels of harvest. Indeed, “present-day harvests for food and bait have reached unprecedented levels and the threat this poses is augmented through motor-vessel use by fishermen […]. Currently, an estimated 5,000 chicks are taken from their nests on Raso and Branco each year. The species may also suffer predation from introduced species such as cats.” (BirdLife International, 2016).
If the 2001 estimate of 30,000 Cape Verde Shearwaters still holds true, then I saw about 18% of the world population this morning (24/4) while having coffee at the Calao terrace in Ngor, when at least 5,500 birds were visible from the Calao terrace, either passing through towards the NE, or feeding out at sea. A week ago I estimated about 1,100-1,200. Sure, some of these were Scopoli’s Shearwaters, though based on the few birds that were close enough to identify and going by our sightings from the boat about a week earlier these would account for 5-10% only. The species arrives on its breeding grounds from February-March, but egg-laying and incubation take place in May-July so the birds that are at Ngor at the moment may still head to Cape Verde – unless they’re all non-breeding birds of course. The species’ presence off Dakar seems rather unpredictable, but late winter and spring (Feb.-May, even June) is obviously the most reliable period to see them here; in certain years there are also good numbers in November (cf. Senegal Seawatching website).
Scopoli’s Shearwater Calonectris diomedea
There were probably 10-20 birds in total, mixed in with the Cape Verde Shearwaters and mostly seen sitting on the ocean surface, and as such I have less useful pictures to share here. A shame because I’m not entirely sure that there weren’t any Cory’s Shearwater C. borealis as well, given that some birds looked really large and heavy-billed. Both species – formerly considered subspecies of Cory’s – share the same overall appearance of a large, grey-headed shearwater with a flashy yellow bill. Differences between the two are subtle and as such one would require good views or photographs in order to positively identify these birds; those see at a distance or under poor conditions are best left as Cory’s/Scopoli’s Shearwater.
The underwing pattern of Scopoli’s Shearwater is probably the most reliable field character, with the hand being less black and lacking the clear demarcation between the withe primary coverts and the dark primaries, which have white inner webs. This is often hard to see as flying birds are constantly shifting and often hold their wings down, hence the need for good pictures. Another feature of Scopoli’s is that is has a single black spot near the base of P10, whereas Cory’s has two on the outermost primary coverts (the 2nd one being detached from the dark edge of the wing – again, difficult to see other than on photographs). The size difference between Cory’s (which is slightly larger) and Scopoli’s is not very useful given that there is overlap and apparently much variation.
The picture below shows two Scopoli’s and one Cape Verde Sheawater: note the pale “hand” on the bird in the background, and yellow bill clearly visible on the bird in the front
A good feature to pick up Scopoli’s among a group of Cape Verde Shearwaters, besides an obvious size difference and the yellow bill, is the much paler appearance of the head, mantle, and side of breast.
The upperwing is clearly more contrasted than Cape Verde, with a dark zigzag across the otherwise grey wing, and mottled brown/grey saddle. This is especially true for Scopoli’s which is said to be greyer than Cory’s:
As mentioned earlier, some birds looked really massive, including the thick bill, but I could not get any conclusive Cory’s – only a few suspected birds such as the one below. A shame that the underwing pattern isn’t clearly visible on this one:
Further reading on separating diomedea and borealis can be had here and here, among others. There’s nothing much to be found on the occurrence in West Africa given that most records are of “Cory’s Shearwater” in the old sense, without distinction between the two species as currently recognised. Most records are from October-November and again around April, but the numbers are quite variable from one year to another. In 2016, we witnessed a strong passage of presumed Scopoli’s throughout November, but no birds could be labelled as obvious Cory’s.
Skuas – another tricky ID category – may follow in a later post!
(post updated 24/4)