Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 6-2-2007)

probably hybrid Herring Gull x Yellow-legged Gull (argentatus x michahellis) 3cy, November 28 1999, Westkapelle, the Netherlands (51.33N-03.25E). Pictures by Pim Wolf.

This individual much resembling a known hybrid Herring Gull x Yellow-legged Gull: EP30. 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. 

The bird in this image also shows intermediate characteristics advocating a hybrid. Most of the greater and lesser coverts still show an obvious immature brown barred patterning, although a few inner greater coverts have been replaced again in the partial moult in autumn and now appear grey-based. The partial moult is extensive, including the three upper tertials, the three inner greater coverts, most of the median coverts and the inner lower lesser coverts. The new feathers are grey-based with a dark arrow-head pattern. All scapulars are plain grey, creating a "saddle-effect" on the back.

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). Some birds continue to moult upper tertials, inner greater coverts, median coverts and lower lesser coverts for fourth generation feathers.
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. As can be seen in the image, the innermost secondaries (not tertials) are plain grey with a white tip, typical for third generation feathers. The iris is pale brown-yellow. 

All comments on this bird (and other supposed hybrids) are much appreciated.

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 EP30 3cy argenteus x michahellis in October-November.
	Link to hybrid EV65 4cy argenteus x michahellis in April.