I’m sorry for the long delay in replying to your comments. There’s no internet connection at Isla Perdiguera! This is also my excuse for having been so long in getting round to posting the next part of Roxanne’s article.

Clive, I have spoken to our friend. He does not know the name of the poison which is doled out to the gulls but he said that it is used selectively and in a very controlled manner, the aim being to ensure that it cannot enter the food chain. The poison is deposited adjacent to the nests of the intended victims, the birds return and eat the bait… and half an hour later the “biologistas” round up the corpses.

As Roxanne says, it seems particularly unfair that they should choose to cull the birds during nesting time - although it is possible that they only do it to birds with unhatched eggs. Indeed, one likes to think that this must surely be the case…

It isn’t nice, but then killing and culling never is, and so far as these people are concerned they are doing it in the interests of preserving an endangered species - the Audouin’s. Having now watched the yellow-legs in action at their nesting site I have to say that any other species sharing the same rock would certainly be in mortal danger. Adult Audouin’s are perfectly capable of holding their own against the yellow-legs, but a chick would be regarded as fair game / dinner. The yellow-legs even attack the young of their own kind, although so far as we have been able to tell they aren’t actually cannibalistic.

There are a lot of dead gulls on Perdiguera, and every week or two we find a new cadaver. Based on what we have now been told it seems clear that these are not the work of the Naturalists. Our friend reckoned that one death per fortnight was about par for the course with a colony of this size. He said that the birds die through having eaten the wrong sort of things at the dump.

As we have seen, gulls certainly do eat some stupid things… but the sick gulls that we encounter appear to be dying of an illness rather than through bowel obstruction. (Mind you, having said that, I don’t know what the symptoms of ingesting a plastic bag might be.) I guess that the dump is full of all sorts of unsuitable things, and all sorts of rotten things too. Gulls are probably almost as susceptible as we to salmonella - and to botulism.

As for the Audouins - no, I don’t see that the yellow-legged gulls could be responsible for the decline in their numbers. The two species certainly share nesting sites, but so far as I can gather (having done a very small amount of research on the web) there is no hard evidence to suggest that yellow-legged gulls regularly kill Audouin’s chicks. If the available supply of food was insufficient to meet their needs then I suppose they might attack the Audouin’s, but as it is there is a plentiful supply of “easier game” at the local dump.

I would imagine that the decline in numbers of Audouin’s might be related to a decline in fish stocks - because these guys are not scavengers; they only eat fish. That having been said, numbers of Audouin’s are said to be increasing now. There are two new colonies in the vicinity of the Mar Menor.

Jill

Great work Roxanne…do you think that the dive bombing nest defence tactics may depend on the age and experiences of an adult bird? Maybe those that do not bother to attack or just make a feeble attempt are older birds and the fierce ones are first timers…or even vice versa!

Take good care,
Sue

Excellent field report and observations Roxanne… I am looking forward to the next instalment…

I would be interested in the name of the chemical used in the poison bread that you have mentioned. Placing any kind of poison bait down in any environment also has an effect on other wildllife. (Normally negative)… I would also like to know if the yellow leg is totally responsible for the decline of the audoin… If it isn’t what is?

Clive

Patrick - do you get seagulls in Madrid?