Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 10-10-2010)

(2 images) hybrid Herring Gull x Yellow-legged Gull 3cy EP30 (argenteus x michahellis), October & November 1999; August 2007, Westkapelle, the Netherlands (51.33N-03.25E). Pictures: Pim Wolf.

EP30 was born in the Netherlands and ringed as pullus in the colony of Neeltje Jans on June 23 1997, most likely an offspring of a true male michahellis (ringed orange EAY8) and a female argenteus. Remember however that theoretically another individual could be the father. Nevertheless, some intermediate characteristics advocate a hybrid. The primary moult score is high with all primaries P1-P10 fully grown (PMS: 50). Most of the greater and lesser coverts show an obvious immature brown barred patterning, although quite some feathers seem to be moulted again in the partial moult in autumn. As can be seen in the bottom image, EP30 is again moulting the outer lower lesser coverts in November. The partial moult is extensive, including the two upper tertials, the two inner greater coverts, most of the median coverts and the outer lower lesser coverts. The new feathers are plain grey. All scapulars are plain grey as well.

From June to October, a complete moult will bring both 3cy michahellis and 3cy argenteus in so-called "third winter" plumage. By October, when the complete moult is finished in argenteus, the head will show extensive 'winter streaking', mottled brown contrasting with the white breast as in an executioner's hood. The scapulars and mantle are pale adult-like grey.
By the end of the complete moult (October), all wing-coverts have been replaced, most to plain grey feathers. Immature patterns can often be found in the lower tertials, greater coverts and outer lesser coverts (the carpal edge).
During the summer, the primaries were moulted to third generation. The first inner primaries are dropped by late May and the outer primary P10 will be dropped by late August. The primary moult is completed by late-October in argenteus, when the new outer primary P10 is fully grown. The third generation primaries are clearly adult-like, with the inner primaries P1-P4 plain grey with a white tip. The outer-wing shows a clear black triangle, extending on the greater primary coverts. From P4 outwards, the primaries show a black sub-terminal band. The white primary tips are obvious in the inner primaries, but often smaller on P9 and P10. P10 has a small white mirror (lacking in some birds). The new tail-feathers will be white, with clear immature black markings. The iris is pale brown-yellow. 

image above: 3cy EP30 (argenteus x michahellis), October 25 1999, Westkapelle, the Netherlands (51.33N-03.25E). Picture by Pim Wolf.

image below: 3cy EP30 (argenteus x michahellis), November 07 1999, Westkapelle, the Netherlands (51.33N-03.25E). Picture by Pim Wolf.

As can be seen in the image below, the head shape and general appearance recalls argenteus. The grey tone on the upper-parts is only slightly darker than average local Dutch Herring Gulls (argenteus). Note that the partial autumn moult is still in progress in the outer lower lesser coverts by early November. Note the colour of the legs, which have only a hint of yellow.

images below: 11cy EP30 (argenteus x michahellis), August 13 2007, Westkapelle, the Netherlands (51.33N-03.25E). Pictures by Pim Wolf.

As 11cy adult, in general a pale michahellis...

Link to 3cy michahellis in October.	Link to hybrid EP29 4cy argenteus x michahellis in April.
Link to 3cy michahellis in November.	Link to hybrid EV65 4cy argenteus x michahellis in April.