Phenomenal shearwater passage in the Sea of the Hebrides

To be honest I did have an inkling of what today might bring when I wrote yesterdays blog post! A birder on yesterdays crossing from Castlebay to Oban had reported 25 great shearwaters from the ferry between Tiree and Rum, so I was hopeful that we might also get to see a few of these wonderful ocean wanderers this morning. Perhaps we'd get lucky, even one bird would suffice, but as it transpired, today was one of the greatest experiences in my birding life. Nothing could have prepared me for this spectacle!

It was still dark when MV Isle of Lewis left Castlebay one hour early at 7am. For the first 30 minutes we sat in the viewing lounge and could see nothing through the windows except blackness, but then at about 7:40 in the half light we spotted a couple of auks and at least one shearwater. This immediately piqued our interest because as I joked to Ray, we'd already seen more than we had seen on the entire journey out two weeks ago! A slight exaggeration perhaps, but the fact is, this was the sixth time we had taken this route at this time of year and virtually all of the previous journeys had been disappointing with very few sea birds, so these few scraps so early into the voyage prompted us to go up on deck immediately.

As soon as we arrived on deck we spotted another couple of shearwaters. The first was definitely sooty but the other seemed to have a white belly but didn't look like Manx. A few minutes later another bird with a white belly, this time closer to the boat, and with the light now better we were able to tentatively identify it as a great shearwater. Then there was another even closer and this time we could see it's pale collar and dark cap, no doubt about this one, a definite great shearwater!

Ten minutes later and we'd lost count of great shearwaters! We watched in wonder as a flock of over 50 approached the rear of the boat and then overtook us, every one of them a great. And still they came, next a flock of 20 with a few sooties, and it was still only 8am, just three minutes after sunrise. Over the next 45 minutes we watched as hundreds of great shearwaters went past the boat plus many sooties, but only a handful of Manx. We also spotted at least three large shearwaters lacking the dark cap of greater, clearly Cory's shearwaters, although the pedantic may comment that they could have been the much rarer Scopoli's. 

They were all heading south east amid a dramatic backdrop as we sailed away from Barra.

A few great shearwaters came quite close to the boat.

We were just north of Tiree when the largest flock overtook the boat. Flock is probably the wrong word, swarm would be more accurate, they were just everywhere and counting them was all but impossible. Time to just watch in awe and forget photos and counts. Most were great shearwaters, but there were also a lot of sooties mixed in. 

The silvery underwing of the sooty shearwaters stood out well at times.

A video of the flypast. It needs to be watched on full screen to appreciate the numbers.

A better quality video is on Vimeo here (opens in new window).

By 8:45 we were approaching Coll and the numbers had dwindled to almost nothing, so breathless we retired to the cafe for a well earned cup of tea. In the end we estimated that we had seen 1000+ great shearwaters, 200+ sooty shearwaters, 3+ Cory's shearwaters and single figures of Manx. To put this into context, prior to today I had only ever seen great shearwater on one previous occasion, 15 from the Scillonian last year when we went to Isle of Scilly in our failed attempt to see the red-footed booby. What an experience, I've never seen anything quite like it.

Dramatic skies and glorious scenery, we were looking towards the island of Rum when the largest flock overtook the boat. What a backdrop to such an experience!

The two maps above show the positions of the great shearwaters during our voyage. These are the maps that I sent to the Barra Birders WhatsApp group during the voyage as it was all happening and the blue dots are the exact positions we were at and also indicate the direction in which I was looking. The map on the left was sent at 08:07 to inform them that we had already encountered 50+ great shearwaters. The map on the right was sent at 08:34 when the largest flock went past. So the first great shearwaters would have been a little west of the blue dot on the left, while the last would have been a little east of the blue dot on the right. 

For recording purposes, Barra waters is considered anything within 200 miles of Barra or half the distance to the nearest landmass. In the case of the ferry this means halfway to Coll and the Small Isles (Rum, Canna etc.). The blue dot on the left is clearly less than halfway to the nearest landmass and therefore at least the first 50 were in Barra waters and great shearwater is a new addition to my Barra list.

Also, see my blog post from a sea watch at Brevig on 3rd October (opens in a new window), when I identified an almost certain great shearwater from a video grab.