B5ZE: Larus michahellis

17 October 2023

On 12 August, we published a short entry on B5RY, which, like B5ZE, was also a Yellow-legged Gull (Larus michahellis). Both gulls belong to the same tagging project, so we refer to that entry for those who wish to know a little more about the species, as well as the purpose and the tagging project with which both individuals are associated.

https://novafalcons.com/en/blog/55-b5ry-larus-michahellis

The personal history that we can know about B5ZE through the code on his ring tells us that he is a male. He was captured and marked as a breeder in the colony that this species has in Illa des Bosc (Eivissa), on 8 April 2021; this being the first recorded observation since the date of marking. The date of the appointment is 18th September, in Port d'Eivissa, where we carry out the fauna control service.

As we have already mentioned above, in the B5RY entry we have explained what the project consists of and the purpose of the tagging, as well as trying to get to know this species a little better, which in some respects could be said to be an unknown species despite how familiar it is to us. So in this case, we are going to take the opportunity to try to get to know a little more about the islet where this male has his breeding colony.

Illa des Bosc

This is a small islet located off Platges de Comte, in the northeast of Eivissa, with a surface area of around 2,300 square metres. It is estimated that it was separated from Ibiza around 6,000 years ago. It is not inhabited, its only construction is the remains of an ancient wall whose purpose is not entirely clear (it could have been part of a larger defensive structure), and like the rest of the islets surrounding the larger islands of the Pitiusas, access to it is restricted to authorised personnel. This is a totally necessary protection measure, as the islets are very fragile ecosystems, where in some cases there are endemic animal and plant species (unique species in the whole planet); as well as being, frequently, nesting places for different birds, as in this case, the yellow-legged gull. It has also been documented, through various scientific ringing campaigns during the migration season, such as the one that SOM has been carrying out since 1995 on Illa de l'Aire (Menorca) in spring, that some islets, due to their characteristics and location, are very important resting points in the migratory flows of dozens of bird species.

Illa des Bosc is physically connected underwater to the other island to the north, Sa Conillera (larger in size), so you could say that it is a kind of "extension" of it, but with a smaller variety of types of vegetation and lacking trees (paradoxically, the forest that gave it its name in its day no longer exists). This island, by the way, has also been the subject of scientific ringing campaigns during the migration season in the past. For those who do not have in mind a clear dimension of the complexity of the Pitiusas archipelago, apart from Eivissa and Formentera, there are more than thirty small islands and islets surrounding both islands, where there are, in many of them, unique subspecies of the Pitiusas lizard (Podarcis pityusensis), one of the most threatened environmental values nowadays in the Pitiusas archipelago due to the presence of invasive snakes.

For those who are not familiar with this subject and are interested in it, you can consult the entries we have in the divulgation section dedicated to this topic.

Having made this very brief approach to the breeding area of our friend B5ZE, and without the need to extend this brief note any further, we leave you with a small "book" of B5ZE: