Survival of wintering Black-headed Gulls in Dutch cities.

Systematically collected readings from overwintering Black-headed Gulls in Dutch cities are very useful for calculating the annual survival of these birds. The data on survival of individuals which show site fidelity (0.80-0.83) agree very well with data which where found elsewhere.
This implies that the observed reduction in the population size is not due to a decreased survival of the birds which overwinter in The Netherlands. In addition to this, from our research it is clear that systematic ringing and reading colour rings provides many and very precise data within a relatively short amount of time.
Furthermore in this species too, it is a very useful technique which is far more efficient than reading individuals which carry a metal ring only. For an elaborate article see Limosa 78 (2005), which can be downloaded, see the header ARTICLES. With a survival of 80-83%, this means that Black-Headed Gulls on average will not become much older than 5-6 years. However, every now and then there are birds which are around 20 years old.
A single individual can even reach 30 years! In the summer of 2009 Benny Middendorp in Zoetermeer and Klaas van Dijk in Groningen observed two of these senior Black-Headed Gulls.

Black-Headed Gull from more then 31 years old.
Zoetermeer, breeding colony Benthuizerplas en Noordhovense plas. Zomer 2009 (photo Benny Middendorp).