Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 7-3-2007)

(2 images) Herring Gull 3cy ? (argentatus), July 13 2003, Tampere, Finland (61.31N, 23.43E).

A difficult bird, both in age and taxon. Maybe argentatus, but it in some respects it resembles cachinnans. The advanced grey upper-parts suggest 4cy, but the primaries and secondaries are more in line with 3cy. The small size suggesting a female. Age and taxon are difficult, but a few features are visible in the images.

Age probably 3cy:

• Secondaries just visible in the central greater covert gap. They have extensive dark centres with the white tips almost completely worn away. In all respects, these secondaries resemble old second generation feathers, as is the case in 3cy July birds. In 4cy argentatus, the third generation secondaries may show dark markings, but this is often vermiculated at the tip, see e.g. a very immature 4cy ringed in Finland CA444. More often, the third generation secondaries are rather plain grey with white tips, see e.g. C68J1.
• The tail-feathers show a broad sub-terminal band and many isolated dark markings at the base. This is the typical pattern in second generation rectrices, but very similar patterns can be found in third generation tail-feathers. See again CA444. However, the common pattern in third generation tail-feathers in 4cy (argenteus) are white feathers with only limited dark markings, see e.g. H-108929.
• The old primaries are hardly bleached brown, still dark blackish without obvious mirror on P10. Both in the field and on the images, this mirror is absent. This is what can be expected in second generation primaries, although argentatus sometimes has no mirror on P10 in 4cy. 
  Another indication for 3cy is the high primary moult score for mid-July: P9-P10 still old and P5 fully grown. P6 is at half of the final length, at the length of P4. P5 has a complete sub-terminal band.
• In the tables below, the primary moult scores of 3cy July argentatus in Finland can be read:

Taxon: some features point to cachinnans, but may still apply to argentatus as well:

• complete white under-parts.
• sloped forehead.
• If age as 3cy is correct, it has very advanced grey upper-parts and wing-coverts compared to average 3cy argentatus.