Range expansion of the Mediterranean Gull Larus melanocephalus: Probability of success in Bavaria

Several records of the Mediterranean Gull suggest that this species may expand its range.

However, up to now none of the breeding attempts resulted in a permanent expansion of the range size. We suggest three hypotheses to explain this low success:

1. The population size of the Mediterranean Gull within the central parts of its range is too small to produce a sufficient number of colonizing individuals to form successful founder populations.

2. Founder populations of the Mediterranean Gull suffer from competition with the Black-headed Gull.

3. Colonizing individuals of the Mediterranean Gull hybridize with the Black-headed Gull and get absorbed into residential Black-headed Gull populations.