Author: Mike Alibone

I was driving through Newnham, already on my way to the gull roost at Boddington Reservoir, when Gary Pullan – god bless him – phoned me with a message of just two words: “It’s here!” he said. Having visited the site twice yesterday and spent the last two hours of daylight shivering in the falling temperatures without it showing, it was comforting to know the adult Bonaparte’s Gull was there and on view.

While Gary continued to spread the word I stepped up a gear, unashamedly broke the speed limit, and arrived shortly afterward to find just a handful of birders watching it. It was with about two hundred Black-headed Gulls. A cracking little gull (or should I say small gull), the proportions of which can be appreciated when compared with the accompanying Black-headed Gulls, numbers of which had built to well over 1000 by dusk.

It spent most of its time at rest, flying only a short distance on a couple of occasions. It may be something or nothing but most of the time it held its bill in a horizontal, or slightly raised, position compared to the Black-headed Gulls, which (most of the time) held their bills pointing down, below the horizontal. I don’t know if this might be a useful way of picking it out among Black-headed Gulls at a large gathering such as the Boddington roost – this needs testing.

There are about 180 records of this North American species for the UK but they are rare inland and this is the first for Northamptonshire, although the neighbouring counties of Warwickshire and Oxfordshire have had two and three records respectively. Well done Gary for finding it on Thursday and thanks are due to Bob Bullock for the accompanying images – which are better than my digiscoped stills – but I did manage to get the videoscope footage below.

Hanging out on boats, buoys and just about anything which provides a suitable loafing site, since late August a fourth-winter large, white-headed gull has been almost resident at Pitsford Reservoir’s yacht club. Identified by some as a Caspian Gull, it exhibits a suite of features which are not fully consistent with that species and which hint strongly at mixed parentage. It can be safely aged as a fourth-winter as it closely resembles an adult but it has retained extensive black in the primary coverts and alula while the rather liberally ‘messy’ appearance of the bill, with a yellow tip divided from a pale, washed out base by a diffuse, dark subterminal band, is also a pointer to its not being fully mature.

Pro-Caspian features exhibited by this individual include the rather elongated body with a high-chested appearance and attenuated, sloping rear end, long, thinnish legs, largely white head (although there is a dark ‘eyebrow’ with some fine streaking on the ear coverts) with a restricted shawl of dark streaks on the hind neck, ‘Common Gull grey’ mantle and a washed out, green-tinged, yellow bill.

Conversely, anti-Caspian features are the absence of a long white tip to the upperside of the 10th primary (instead P10 has a very small white tip), absence of a long white tongue on the underside of P10 (where there is a single mirror set into an otherwise black distal end to the primary), broad – as opposed to fine – rear neck streaks, a rather deep, powerful-looking bill with a strong gonydeal angle and a sharply-angled and hooked culmen, a pronounced pale straw-coloured iris and a relatively large, ‘full’ head, lacking Caspian’s long, sloping forehead and ‘snouty’ appearance.

While pale eyes do not rule out Caspian Gull (a minority exhibit pale irises) and variation in wing tip pattern can be considerable, bill structure, head shape and jizz normally remain consistent and combine to lend a more ‘gentle’ appearance far removed from what we are seeing here. This individual appears to have a head shape, bill structure and a general ‘mean’ character much closer to Herring Gull or Yellow-legged Gull than to Caspian Gull.

However, the wing tip pattern is very similar to a known 4th year male Caspian Gull from Poland (see here) although the Pitsford individual has larger white primary tips. Interestingly, in threatening behaviour toward other gulls, this bird calls with its wings partly open, the bill pointing down initially before raising it to 45 degrees as it delivers a very convincing Caspian-like laughing call and posture.

It is easy to speculate but difficult to draw any firm conclusions but I would guess this individual comes from the East European hybrid zone where mixed pairs of Caspian Gulls and Herring Gulls of the ‘Scandinavian’ race argentatus are known to occur. Hybrid Caspian Gull x Herring Gull from this zone has occurred in the UK before see, for example, here .  However, it can also appear quite square-headed and sometimes takes on the appearance of Yellow-legged Gull, although structure and jizz are not quite right for that species. It is an interesting individual but it is certainly not a pure Caspian Gull. Watch the video below. What do you think? Comments welcomed.