Vleugelontwikkeling bij grote meeuwen in de kuikenfase: een handleiding

Chicks of Lesser Black-backed Gulls and Herring Gulls grow rapidly from small downy young to fledglings over a period of just over 40 days. The physiological changes, internally and externally, proceed with different growth rates: a change from a “digestive system on legs” during the first weeks to a feathered flying machine when the colony is about to be abandoned. During studies in a mixed colony of these gulls at Texel, we monitored the growth of chicks by measuring body mass and a number of structural size parameters (including wing length). In the absence of a protocol, we did not monitor for example the development of flight feathers. With hindsight, we regret this, because chick development and chick growth is more than just an increase in length or volume. From a sample of 64 collected chicks (2009 season) we describe the stages of flight feather growth with age and with structural size and suggest a simple coding system, based on the feather score system, to describe the development of wings in the field in future studies. As a result of our collected material (dead chicks, including chicks with growth deficiencies), we expect that our age-windows for each of the stages are too wide. Further fieldwork, using healthy birds that fledge, will refine these windows, after which a good idea of chick age can be obtained when visiting colonies during the breeding season, simply by checking the progress of feather development.