Heuglini 2cy, February 26 2001, Bahrain: Ashkar harbour. 

Extensive streaking on head, neck, sides of the breast all the way down on the flanks. Mantle and scapulars are second generation plain grey feathers with a pronounced black shaft. Most of the lesser and half of the median coverts are moulted to second generation feathers, which show a barred pattern. The inner greater coverts are replaced but almost all are missing and when full grown- these greater coverts will appear as a fresh panel of new feathers. In most of the heuglini, wing covert moult is still in progress by the end of February. The inner primaries are all dark, without a paler window. In the background is an adult heuglini.

In Bahrain, such large birds with almost parallel bills are either cachinnans or heuglini. Cachinnans, being a southern breeder from the steppe belt, normally doesn't show such active post-juvenile moult in February. Moreover, most cachinnans have finished their post-juvenile moult by early November as 1cy birds. Hence, active post-juvenile moult in February in 2cy birds is a strong indicator for nortern breeders from the tundra region, i.e. heuglini and fuscus in Bahrain.