Sunday 3 May 2020

From the Archives - American Black Tern at Farmoor Reservoir Oxfordshire 29th August 2009

Juvenile American Black Tern c Ian Lewington
We Oxfordshire birders are fortunate to have Ian Lewington, a noted seabird identification expert and bird illustrator supreme, as our County Recorder. On a visit to Farmoor on Thursday 27th August to check out a reported juvenile White winged Black Tern Ian found what appeared to be four juvenile Black Terns and the White winged Black Tern. The plumage of one of the four Black Terns was troubling, so Ian took some video of it and later on that evening on reviewing the video at home identified the tern as an American Black Tern, only the third to be recorded in Britain.

Meanwhile I was birding in Norfolk with Hugh, a long time birding colleague, on Friday 28th August, when the news filtered through to us that an American Black Tern had been found, almost unbelievably, in the company of a White winged Black Tern and a normal Black Tern at my local Farmoor Reservoir in Oxfordshire. This occurence was totally unprecedented, had to be unique and certainly was something I wanted to see but I was committed to spend two days in Norfolk with Hugh and as he was a good friend I did not want to let him down.

I tried to put the sensational news to the back of my mind and managed to forget about it, well almost, until the next day Saturday 29th August, when whilst seawatching at Cley with Hugh, someone mentioned the American Black Tern was still at Farmoor. After some animated discussion with Hugh on what to do I decided had no choice but to stay put as I had to drop Hugh back in Norwich that afternoon. My somewhat fragile hope was that the tern would remain at  Farmoor for one more day, as migrant terns will often stop over for a few days at the reservoir in late summer. I would be at home the next day and able to make the short drive from my home to see it first thing in the morning. Well that was the plan!

Having made my mind up on this course of action and with Hugh needing to be back in Norwich by 3.30pm on Saturday, I duly dropped him off in Norwich and then, as will be familiar to many a birder, threw all my plans out of the window and decided I could make it to Farmoor by that evening although it would be tight. I calculated I could get to Farmoor by 7.30 pm, assuming, and it was a big assumption on a Bank Holiday Saturday, the roads would be reasonably fast and clear of hold ups. I was incredibly lucky with the traffic and despite the fuel gauge running perilously low as I neared the end of my four hour journey, I had made such good time I arrived at Farmoor at 7.15pm. 

The three terns had been reported from Farmoor Two, the larger of the two reservoirs, so to save time and a long walk I drove to the back of Farmoor Two and jumped over the fence. I scanned the reservoir and thought it strange there was no-one about and even stranger there were no terns to be seen. Surely something was amiss? Had they flown off? I looked across Farmoor Two to the central causeway that runs between the two basins  that constitute Farmoor Reservoir and found a small huddle of birders halfway along the causeway, with their backs to me, obviously looking at something on the smaller reservoir that is Farmoor One. It had to be the terns. They had moved reservoirs! Damn it. My anxiety levels rose rapidly but there was still time. I raced back to the car and drove the short distance round to the reservoir's main car park, very conscious of the fact that time and daylight were running out.

I ran up the incline onto the concrete perimeter track of the reservoir and then ran up the causeway. After what seemed an age I got to where the birders had been but there were now only two left neither of them local. I enquired of one if he could see the terns but he, like me, had arrived just a few minutes ago and appeared not to know what he was looking for and told me he had been told by some departing birders the terns were still here, somewhere amongst the gulls but he could not find them. 

It was apparrent I was going to have to do this myself which hopefully would not take too long. Would there be time? I looked through my bins at the swirls of gulls, more in hope than anticipation, but it was surprisingly easy and quick to locate the trio of terns, flying in and out, above and below the numerous Black headed Gulls that were assembling to roost on the reservoir. 

Having found the terns I now needed to identify the American Black Tern, a species I knew little about and had never knowingly seen before. From a conversation with another birding friend on the drive from Norfolk I had gleaned the information that a juvenile American Black Tern had smudgy grey flanks and darker upperparts and this particular individual kept in close association with the White winged Black Tern.

Juvenile American Black Tern c Ian Lewington
Again it was relatively easy to differentiate between it and the White winged Black Tern but slightly less so with the Black Tern as all three flew around together. In fact their close association made it an ideal situation to make comparisons. To my eyes the American Black Tern was darker than both the other terns, very much more so in the case of the White winged Black Tern which was much the palest of the three, especially on its head and rump, with clean white flanks and underwing coverts and an obvious chestnut mantle contrasting with pale grey wings. 

Juvenile White winged Black Tern c Ian Lewington
The American and White winged Black Terns definitely appeared to favour each others company and frequently all three terns would be close together and you could say that for the main part they remained as a loose group, as they followed each other around the reservoir.

The American Black Tern was distinctive once you got 'your eye in' showing darker upperparts, especially on the lesser coverts and secondaries than the Black Tern and with more extensive greyish brown smudging on the sides of its breast and an uneven greyish brown band running along the flanks.The rump and tail were also darker than the Black Tern and showed much less of a contrast with the mantle.

Juvenile American Black Tern c Ian Lewington
I watched this unlikely trio for as long as possible before the light became too dim and finally departed Farmoor, happy with this momentous and unexpected end to a birding trip that had started in Norfolk three days ago.
Comparison of  juvenile American Black Tern and Black Tern at Farmoor c Ian Lewington
The three terns remained at the reservoir over the entire Bank Holiday, allowing hundreds of birders to come and see them. I re-visited them twice more during their stay, getting extensive views of them both flying and perched on the straw bales used as water filters on Farmoor One. When settled on the bales the American Black Tern appeared to be slightly smaller than the Black Tern. 

They were last seen on the evening of 3rd September when all three departed high to the south east at 7.50pm.

My grateful thanks to Ian Lewington for allowing me to use his images of the terns in this blog and the plate he made to go in Birds of Oxfordshire 2009.

No comments:

Post a Comment