Feature: Baltic Gulls passing western Norway

October migration of Baltic Gulls in western Norway

The Lesser Black-backed Gull Larus fuscus intermedius is a rather common breeding bird in Hordaland county. They arrive during April, and most adults have left by mid September. The species is a scarce migrant in October. During a seawatching session at Fedje in western Norway 5 October 2015 an epic 82 adult birds were seen migrating during the morning. I focused on photo-documenting the moult stage on the birds passing by. Given the general opinion on moult differences in Baltic Gull Larus fuscus fuscus and western birds Larus fuscus intermedius/graellsii, approximately 30 Baltic Gulls passed my watchpoint during the two hour session! There are no accepted records of Baltic Gull in the county.

Notes on subspecific ID of adult Lesser Black-backed Gulls in October

Moult

The cruicial feature is the timing of the moult. Lars Jonsson (1998. Baltic Lesser Black-backed Gull Larus fuscus fuscus – moult, ageing and identification. Birding World 11: 295-317) states that adult Lesser Black-backed Gulls in our region are best told apart in autumn. A Baltic Gull is moulting its primaries later than the western intermedius/graellsii, and at this time should have all 8-10 primaries retained. In the following this is the rule for subspecific ID. However, there seems to be a lot of variation in apparent Baltic Gulls photographed in Israel in October (watch this link), and my gut tells me that several of the intermedius below actually may be fuscus.

Proportions and coloring

Color and proportions. Both rather cruicial Baltic Gulls are slim and contrasty. Their mantle color is almost as black as the primaries, but this is hard to judge. I felt like most birds were really dark with almost no visible contrast, but the light (morning sun) may have puzzled me. Baltic Gulls are also slimmer, and has proportionally longer wings. All in all a slender and delicate gull, some of them only a bit larger than the passing Common Gulls Larus canus.

Bird 1: The bird has shed the four inner primaries, and all are growing.

Larus fuscus intermedius

Bird 2: All primaries appear as of the same generation, and none are growing.

Larus fuscus fuscus

Bird 3: The bird has possibly shed p1. The rest of the primaries are of the same age, and look abraded.

Larus fuscus fuscus

Bird 4: All primaries on this bird are old, intact and abraded.

Larus fuscus fuscus

Bird 5: Seven primaries are shed, and the refreshed ones are almost grown. This in addition to the very pale mantle suggest this bird a

Larus fuscus graellsii