Melanistic Cory's shearwater off Cape St Vincent

Ok let me start by saying that this is a controversial post. This bird has been debated on the internet and some people seem to think that this is just a normal Cory's shearwater and the dark look is created by light conditions. They're allowed their opinion. I think they're wrong and I'm allowed my opinion, especially since I'm the only person who saw this bird in the field. Everybody else is going off just the photos. However, if you're researching melanistic Cory's shearwaters and come across this post, please bear in mind that not everybody agrees with me so perhaps it would be simpler to just forget this bird. Or maybe make up your own mind.

We were perhaps 30km out from Cape St Vincent when we came across a feeding frenzy of Cory's shearwaters. In the middle of them I saw a dark bird and my immediate impression with my naked eye  was that it was a sooty. In otherwords, it was much darker than the Cory's and unlike them it had a dark belly. I fired off a few photos which I then looked at and realised that it was actually a Cory's on size and structure. Then I looked up and the bird was gone. I was on a dolphin and whale watching trip, it wasn't an option to ask the skipper to go hunting for the bird. There were no cetaceans here to satisfy the other punters so we moved on. To be honest I wasn't particularly interested in looking for it myself.

So ignoring the fact that I've just said that it had a dark belly and I initially thought it was a sooty, which should be proof enough on it's own, let's look at the photos.

Firstly, let me make it clear that every photo I took is here, I haven't just cherry picked the ones which look darkest. There isn't a collection of photos hidden away on my laptop which show a white belly. Everything is here.

The photos show the bird flying left and right, raising up and flying flat. In every photo it is the darkest bird by far. I don't need to tell you which one it is, you know as soon as you look at each photo.

Unfortunately I didn't manage to get any photos of its underparts and that's the main issue. However, in the photo at the top of this post (cropped here) you can see that it has a very dark head, face and throat. None of the other shearwaters show this. The bird below is a typical Cory's. Look at the difference.

In this photo the bird is flying up with a typical Cory's and you can see that they are the same size, they're flying close to each other. Not only that you can see plumage detail on the dark bird. This isn't just a silhouette. 

You can actually see that the head of the dark bird is catching the sun yet it still looks much darker than the typical Cory's behind. If anything it should be burnt out not look darker. You can also see that the birds uppertail coverts and mantle are catching the sun. It's not in shadow. Look at the colour of it's head compared to the bird behind! There's no comparison. If the dark bird only looks dark due to the light, then how come that the bird directly behind looks so pale?

In this photo the birds uppertail coverts are catching the sun even more and you can see the sun is on the birds back, yet it still looks dark. If this was an affect of the light the mantle colour if anything would look lighter in these conditions. 

So now the bird has changed position entirely it's no longer going up and right, now it's flat and flying left. Every other bird in the photo looks pale, how does this bird remain looking dark no matter what the angle. Maybe because it is dark?

What I find really hard to comprehend is the fact that there are people out there who say that this is a typical Cory's! Whatever it is, it's far from typical and it cannot be explained away by light conditions.

Now it's lifted it's wings and they still look just as dark. 

In summary, in my opinion this is a clear and obvious melanistic Cory's shearwater which was off Cape St Vincent on 27th September 2026.