When dealing with LBBG of unknown age, it is often difficult to distinguish between 'sub-adults' and 'adults'. In Hering Gull, the presence of black on the primary coverts is often used as dividing character. Obviously, in LBBG the sole presence or absence of such black markings is not enough. But maybe the pattern itself can be used?
AIM: to draw a line between what can be considered sub-adult birds and adult birds, based on primary covert pattern. Therefore, note extent of black, presence of brown hue and patten of the tip of the greater primary coverts.

These pages illustrate that black markings can be found in both immature birds (4cy and 5cy breeding birds at Moerdijk), and in 'mature adults'. These pages also show several mature adults with black-brown allula, a feature sometimes used to distinguish between sub-adults and adults.

All these LBBG are breeders at Moerdijk in 2005 & 2006. Pages show primary covert patterns. All illustrated birds are retrapped individuals (except some 4cy birds). Some of these breeders may have been ringed as pullus, other birds were previously ringed at older ages. See more information, by clicking the thumbnails.

Several images have been flipped horizontally and in fact these show the right wing. Pictures were automatically generated in Photoshop, and may not reflect original greytones; please use these images only to measure black on the primary coverts.