PHOTO SPOT- COMMON TERNS AT PENNINGTON FLASH

by Ian McKerchar

All images by John Tymon

During the late summer of 2007, long time county birder and original Pennington Flash 'moocher' John Tymon took literally hundreds of photos of the Common Terns present during this time at Pennington Flash. I have reproduced several of those photographs here, not only to exhibit John's hard work but also to illustrate features of these majestic birds.

Above: adult Common Terns begin their wing moult around July or August replacing up to 4 inner primaries before suspending their moult prior to migration and as can be seen in John's image below the inner four primaries are pure grey and very fresh, whereas the older outer 6 primaries are very dark (almost blackish here, caused by the pale grey colour wearing off to reveal the blackish base colour) and contrast strongly against the newer inners. The primary moult is then resumed in the winter quarters where the remaining outer primaries are moulted and is completed in January to early March when the birds have already begun to grow new inners! Thus the inner primaries are moulted twice a year (late summer and late winter) but the outers only once (early winter) so that when we see the birds in Greater Manchester (and elsewhere in Europe) there is always a contrast between the new inner primaries and the older outers. This is in contrast to the primary moult of Arctic Tern which has a complete wing moult once a year in late winter (prior to the spring migration) giving the species a uniformly grey winged appearance, lacking the dark outer primary 'wedge' of Common Tern.

Above: again this bird has moulted the inner primaries (although it appears to have 5 new ones) but note also the relatively long legs and bill whereas Arctic Tern has distinctly shorter legs and bill.

Above left: an extremely adapt and successful hunter, the primary moult contrast is obvious here but note the faint darker feathering on the carpal bar and secondaries probably indicative of early moult into non-breeding plumage (also note the metal ring on the right leg). Above right: squabbles between Common Terns and Black-headed Gulls are common place especially where space is at a premium but Common Terns are notoriously aggressive and this bird isn't going to give up it's perch without a fight!

Above left: the longer outer tail feathers are visible to good effect here (note also the faint dark markings again on the secondaries in this bird which is the same individual as that above left and below). Above right: the thick and rather diffuse trailing edge to the primaries is obvious here, it would be more clear cut and narrow on Arctic Tern.

Above: the bill of this bird appears to lack the expected black tip of Common Tern and could have proved be a potential pitfall in it's identification. Notice however, that the bill is still too strong and long for Arctic Tern and it's colour too bright a red (Arctic's are a deeper red) and the primary moult contrast is still obvious on the far wing. Although it's head pattern indicates a breeding plumaged adult there were faint darker areas on the carpal bar, greater primary coverts and secondaries, probably features of it's early moult into non-breeding plumage, perhaps it is a failed breeder which tend to begin their moult earlier?

Above: the same bird as above, note yet again the strong moult contrast in the primaries. This bird bore a small metal ring on it's right leg and it would have been interesting to know when and where it was actually born but there have been many cases of birds ringed as chicks at Pennington Flash (and also to a lesser extent from Crompton Lodges, Farnworth) which have subsequently been either re-trapped or had their rings read in the field at Seaforth Nature Reserve, occasionally only a month after being ringed and often returning annually to Seaforth, including breeding there.

Above: here John has captured the distortion to the trailing edge of the outer primaries on the bird's left wing (our right on this image), caused by airflow through the feathers during the bird's powerful strokes in this characteristic hovering manoeuvre whilst it scans the water for fish. Indeed, powerful wings are necessary to propel the bird to it's wintering quarters in Africa, through wind and weather that might keep the less hardy birder safely indoors. In Greater Manchester birds have usually departed by the middle or end of September at the latest and during September and into October there is a strong passage of Common Terns along the Atlantic coast of Iberia towards Morocco, following the coastline southwards down the eastern Atlantic (not necessarily close inshore) towards their major wintering areas offshore between southern Morocco and Nigeria. Adults begin their return journey from these wintering areas from February onwards (immatures generally remain in the wintering areas for their first summer) and finally arrive in Greater Manchester at the beginning of April, rapidly building up at the breeding sites especially.

Above left: the same bird as above, the darker feathering on the carpal bar (the leading edge of the inner wing) is visible here as is the primary moult contrast again. Above right: the longer outer tail feathers are obvious but are still much shorter than those of Arctic Tern.

Above: a juvenile Common Tern showing the pale based bill and strong dark carpal bar of this species although the brownish mantle has worn away somewhat leaving rather rusty edges to the feathers. Arctic Tern in juvenile plumage has an all dark bill, fainter carpal bar and grey upperparts without the distinct rusty edges.

Above: a yawn or a call? The brownish mantle on this juvenile Common Tern is more obvious here and the legs still appear too long for Arctic Tern, should the bird open it's wings it would display fairly distinct grey secondaries unlike the often striking pure white ones found on juvenile Arctic Terns, a very useful feature for separating the two species in flight at this age.

Above: Common Terns gathering on 'the spit', with here, two juveniles and 6 adults (1 hidden below the bottom right bird). Although the spring passage is generally more likely to produce larger flocks of birds the late summer and autumn gathering can too produce good numbers, unfortunately though, breeding successes at Pennington Flash are largely dependant on suitable water levels and the severe flooding over recent summers has hampered their productivity at this site.

Above: two adults and a juvenile. Adult Common Terns begin a post-breeding moult shortly after the young fledge and begin with the body feathers (wing moult not until July or August) and by August and even July may show signs of non-breeding plumage. The far right adult in John's image here is already attaining the white forehead of the non-breeding plumage and perhaps some darker feathering on the carpal bar.

Above: ever wondered just how the Pennington Flash juvenile Common Terns know which direction to fly for their long journey to Africa? Well now you know, 'fly south my son'!

Above: ever the deadly predator, this could well be the very last thing a small fish might see as it looks up but chances are it would never know what hit it!

My sincere thanks are to John Tymon for not only supplying me with his images but for his perseverance in taking them in the first place!

References:

Time to Fly, Exploring Bird Migration by Jim Flegg (BTO)

Identification Guide to European Non-Passerines, Kevin Baker (BTO Guide 24)

Birds in Greater Manchester, County Bird Report 2000-2005

Ian McKerchar, September 2007.

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