Tuesday, March 30, 2021

Eyestrain at Farmoor

For my Oxfordshire birding I have somehow ended up adopting three patches - Port Meadow (the original and the best), Appleford (because of the gulls and the tip) and Farmoor Reservoir. Why I visit the latter so regularly is a mystery to me as I despise birding there - it is a featureless double concrete basin and on a bad day there is very little to even look at. I guess it's close to where I live and very convenient to get to from my office, so I end up popping in a few times a week. What draws me there is the potential for rarity finding, particularly at the roost, where the numbers of gulls eclipse anything seen at Port Meadow - probably at least ten thousand in the depths of winter.

The downside to this is the size of the reservoirs and the fact that the gulls prefer to roost right in the middle of F2, the larger basin, meaning that they are typically several hundred metres distant. To give an idea of just how far away many of the birds are, the video below starts at the maximum magnification of my scope (60x) before using the digital zoom on my phone camera to produce an acceptable record shot of a first winter Caspian gull. 

The distance means that even at 60x the birds are still tiny through the scope, so features like the exact pattern of the scapulars and coverts are very difficult to discern. Combined with the fading light it's an absolute recipe for eyestrain when trying to examine a candidate bird. Therefore at Farmoor, identification of Caspian gulls tends to be based on bulk plumage features (like white head, brown greater covert bar and plain tertials). This means that some of the more borderline individuals remain unidentified, or equally that some minor Herring gull features that might indicate hybrid origin are missed. Nevertheless, it is usually possible to identify most birds in the roost and despite the distant views the sheer number of birds makes for very entertaining roost watching.

Typical views of the gulls on F2.

Since September last year, I've had Caspian gulls regularly in the Farmoor roost - most of these birds are individuals that I've had better views of at other sites in the county, which makes identifying them much easier. I've posted some of these photos before, so here are a selection of birds that I've seen recently, together with some better images of these individuals from other sites!

1w in roost on F2.

Better views at Appleford earlier in the year, although still pretty distant. This is such an amazing bird, the best of the winter by far... that extreme scapular pattern, with just a single dark line following the rachis of each feather, is my absolute favourite plumage type in cachinnans. Interestingly, this bird was dark, with a rather streaky head and dusky underwing.

Massive 1w male on pontoon on F1.

This image was taken by Mick Cunningham, who found this distinctive bird during the day at Standlake. The heavy bill, indicative of a male Caspian gull, is evident here - this is also an extremely large bird. It has been seen at various sites in the county since October.

2w in roost on F2.

Showing P10 mirrors.

Same 2w in the field at Appleford.

This rather indistinctive 1w has been seen regularly at the Farmoor roost and also at Port Meadow - this superb image was taken by Joe Wynn as he chanced on it resting close on a pontoon on F1. Below is a video of this bird in flight over F2, on an evening where it was so windy that the only option was "seawatching" and identifying the birds as they flew into and around the reservoirs! All the relevant features for identifying cachinnans in flight are visible - note the clean uppertail with neat black tail band, white underwing, contrasty upper wing and the obvious neck shawl behind the white head.

A couple of Caspian x Herring gull hybrids were also noted.

This bird was regular in the roost in February and combined the clean coverts and tertials of Caspian gull with a Herring-like head and bill. Perhaps unsurprisingly it bore a yellow ring.

The putative 2w Viking gull deserted the Port Meadow roost at the beginning of March and moved to Farmoor, where it took a strong liking to one of the blue buoys and roosted on top of it each night. Its bulk meant that it was quite dominant over the other gulls and it had no problem removing an incumbent gull from the buoy and then defending its post for the rest of the evening. In the light at the Farmoor roost the uniform beige colouration of the underparts (actually darker than the pale grey mantle feathers) was evident. All equivocal I know as these fine vermiculated plumage features can be shown by pale 2w Herrings. But to have all of them in one bird combined with a Glauc-y structure makes me suspicious and having studied it at length I think there's a pretty strong case for a hybrid here.

Yellow-legged gulls are regular at Farmoor with double-figure counts on some nights, particularly in late summer/early autumn. Some images of 1w birds below.

Small gulls, mainly black-headed gulls make up the bulk of the Farmoor roost and searching through thousands of identical individuals each night can be rather tiresome. Nonetheless there are rewards to be had - these two 1w kittiwakes appeared on F1 after a south westerly blow on 28th October.

Little gulls are regular in spring but much rarer in the winter roost so I was pleased to find these two 1w birds on 8th November.

The main passage of Mediterranean gulls occurs in March with smaller numbers in October and throughout this season I recorded a large number of individuals of all ages. In March, it was rare that I visited the roost without seeing a Mediterranean gull - the status of this species really has changed in the county, with a couple of local breeding pairs.

Numbers peaked at four on 6th March, which included two birds that were obviously paired and engaging in courtship behaviour. This consisted of chasing each other around calling and swimming in tight circles looking intently at each other. Strange beasts. These inseparable birds visited continuously for a couple of weeks and throughout their stay the thinner billed (presumably female) bird acquired a full black hood. 

I've noticed that early passage seems to consist exclusively of adults, with 1w birds only appearing in late March once the adults have petered out.

As well as the gulls, there have been a couple of other surprises - this cattle egret which few north as I was doing the roost on 2nd October was the first record for the reservoirs:

Whilst a ringed common crane from the reintroduction project on 12th March was another a good flyover and a patch tick.

In general, though, good finds have been few and far between... Hard to believe there wasn't a single white winger recorded in dozens of visits to the roost! I hope to rectify this dearth of finds during spring passage. Bonaparte's season is almost upon us and with a 1w bird moving east from Cardiff to Gloucestershire I'm hopeful that it'll end up at Farmoor in the next few weeks!

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