|Yellow-legged Gull PFFF, ringed in Spain, observed at the Porto de pesca (photo: Pedro Moreira)|
On August 28 Pedro Moreira and I went out to search for colour-ringed gulls in the area around Aveiro, Portugal. Our day started at the Eirol landfill, where usually good numbers of gulls are present, especially now that fall migration has started. However, the number of gulls there turned out to be a bit disappointing. We made a very rough estimation of about 3500 Lesser Black-backed, 150 Yellow-legged and 20 Black-headed Gulls; similar numbers as on our visit to the site of August 21. Unfortunately, most of these birds perched on the roofs of the buildings, making it difficult to read their rings. There were moments when the whole pit remained empty from gulls. Only 35 rings were read (fewer than last time). Around noon we decided to leave the place and find out where our birds had gone to.
|An empty landfill|
We passed by the beaches to see if bycatch from Xavega (the traditional fishing where the catch is landed on the beach, see Paul Veron's blog entry about this event: http://guernseygulls.blogspot.pt/2014/08/the-exodus-of-lbbgs.html) was attracting them. But as the waves were too high that day (as on the previous days), there were only few gulls present, all of which were flying over the ocean. Better luck we had at ‘Porto de Pesca’, the largest fishing harbour in the area. Roughly 1500 Lesser Black-backed Gulls were present there, allowing us to read 8 rings on those. Besides these Lesser Black-backed Gulls, about 400 Yellow-legged Gulls were present in the harbour. Of these at least 5 were ringed.
|Lesser Black-backed Gull 'E4', at Porto de Pesca. Ringed in the SW of the Netherlands (photo: Pedro Moreira)|
|Yellow-legged Gull N:1NC, from Spain, observed at the Porto de Pesca (photo: Pedro Moreira)|
|Yellow-legged Gull 1Y5 at the Porto de Pesca; note the worn and open colour-ring, about to fall off (photo: Pedro Moreira)|
Some of these Yellow-legged Gulls, all adult birds, have been seen at the harbour earlier this summer. Apparently the seaport to Aveiro is attractive for this species. With many expanding breeding populations in nearby areas (i.e. Porto), it would be just a matter of time before they start nesting here (assuming that they didn’t do this already). And indeed, we found information that by now Yellow-legged Gulls nest in the harbour!
While searching for rings we noticed two immature Yellow-legged Gulls begging at two adults, which were involved in some kind of social conflict with a third adult bird. With the appearance of our car, the adults started to alarm. Both chicks were able to fly properly and could be considered fledged.
|Two begging Yellow-legged Gull chicks and their presumed parents (photo: Pedro Moreira)|
Of course, observations of begging but fledged gull chicks are by no means good evidence that the chicks were born in the area, as they are capable of following their parents over long distances. However, our suspicion that these were in fact local birds gets supported by the following information I received from Pedro.
|The same begging Yellow-legged Gull chicks and their presumed parents (involved in social interactions with a third bird)|
On August 8 Pedro visited the harbour to read rings and talked there with a fisherman, very close to the particular location. He was told “You are late! You should have come earlier to see the nest!”. Apparently there had been a nest on the dock on a rolled up rope, containing three eggs. Out of these two chicks hatched. It was the first time the fishermen had seen it there. When Pedro approached the location of the nest he got dive-bombed by an adult Yellow-legged Gull. A bit further away he saw a young juvenile (about the same in size as the ones on the photos above). Then Pedro realized he had been dive-bombed at the same location earlier in the summer, on July 17. He never saw the nest but never looked for it either. At inspection of the location on August 28 we did not find any remains of any nest, but by that time it would have been washed away by the elements. It seems probable that the two chicks we observed belonged to this nest.
It would be interesting to see how in the future the migrant and wintering population of Lesser Black-backed Gulls in this part of the world is going to deal with an increasing Yellow-legged Gull population, since competition for food between the two species can be expected. If you happen to know more about nesting gulls in or near Aveiro (and this would not be the first nesting of the Yellow-legged in the area) I would be very interested in this information.
After this encounter, we headed to the Porto de Commercial, where during the high tide a large parking place gets used by the gulls as a roost. 2000 Lesser Black-backed, 500 Yellow-legged and one Greater Black-backed Gull were present. 8 rings were read.
|Part of the large gull-roost at the Porto de Commercial, Aveiro|
This number of gulls however did not explain where many of the gulls had gone to (we still had the impression we were missing many). It may be possible that some of the recently arrived Lesser Black-backed Gulls found a better place at the larger fishing harbours in i.e. Leixoeis or Figueira da Foz, where the larger fishing boats arrive, which are better at dealing with the waves.
|Subadult Greater Black-backed Gull Larus marinus (photo: Pedro Moreira)|