No die-off yet.., just many dead gulls

In response to my announcement of a ‘gull die-off’, Professor Antonio Luis (University of Aveiro) informed me that this part of the Ria de Aveiro is part of a very wide basin, which has several industrial areas, agriculture, cattle, etc. The road network is relatively dense too. It's also known that the lagoon itself is very polluted at some points, from very local sources. On the other hand these were the first rains in a long time, there were lots of wildfires during summer and now there's nothing to hold both the rain water and the burned ground (as well as what's in it). As a consequence everything is easily washed away, down into the lagoon and flood plains. In summer, when the water gets warmer, it's also common to have toxin blooms (shellfish capture is not allowed during these periods) and these maybe nasty toxins sometimes... The number of possible causes may be pretty big.

In order to investigate the true scale of this thing, and whether we’re experiencing a true die-off or not (in which the population undergoes a sharp decline), during yesterdays afternoon I walked 2 km on and along the shoreline and sand dams of the Ria de Aveiro, near the UA. This track included the 300 m transect I mentioned earlier.

On this track I found the remains of a total of 25 Lesser Black-backed Gulls, 5 Black-headed Gulls and one Common Redshank. Most of the LBBG carcasses were old (17 >multiple weeks/months/a year), one was fresh (the affected live adult that I found on October 6) and 7 probably died within the past three weeks. Most (at least 20) of these were adult plumage birds. Of the BHG carcasses (all adults), one was older than months and 4 had died during the past few weeks. I suspect this has been a slight undercount as not all of the tide line was accessible (about 20% remained unchecked). I found one possibly affected live bird, a solitary adult LBBG in the active salinas, which I could not approach. None of the carcasses I checked was marked.

 

 Older, subadult LBBG carcass

At the salinas and in the Ria there were about 450 LBBG and 170 BHG roosting. Later, at dusk, came roughly 900 LBBG and some BHG over my head from the direction of the local landfill, of which a varying number roosts in this part of the Ria.

This would indicate that the scale of whatever is/was going on seems indeed not to be alarmingly large, at least not in this (relatively isolated) part of the Ria, and no immediate action needs to be taken. Just to be sure, next time I’ll try to investigate a slightly more northern area to see how the situation is there (closer to the ocean's entrance, where several dying gulls had been reported earlier). Let’s hope that whatever this is or was has come to a halt by now, as these dying gulls always are a nasty sight. Considering the scale of this event I am very sure that there will be at least some marked individuals among the recently deceased birds. I will try to keep an eye out for those and recommend local readers of this blog to do the same.

Gull die-off in the Ria de Aveiro

Once a week the dog gets a walk along the a few hundred meter long sand dam on the Ria de Aveiro, at the height of the University of Aveiro. On this walk I identify and count fresh carcasses of birds (and once a feral cat). About three weeks ago I started to notice a rapid increase of dead Lesser Black-backed Gulls and Black-headed Gulls. I usually find (depending on the time of the year and the number of gulls present in the area) about 0-1 gull carcass on each trip. Within the past three weeks I found there the carcasses of 10 LBBG (9 adult and 1 immature) and 4 adult BHG. About two weeks ago I spoke with 'Ines', a UA student who also walks with Juli along the Ria at the height of the university. At that time she told me Juli ran onto the mudflats while chasing a dark gull that could not fly. On October 3 I got informed by an inhabitant of Sao Jacinto that he had noticed an unusual high number of deceased and dying LBBG out on the most southern dam of the peninsula, about 7 kilometers from the earlier location. He told me he found 21 gulls of which a few were still alive. These live birds were unable to walk and were turning their heads backwards in an odd way. Today Flor and I walked our transect again and ran into this adult LBBG showing symptoms of poisoning. About 40 meters from us was another adult LBBG present on the water surface which appeared to be trying to fly, though it did not manage. There were no new carcasses present on the transect, but the recent high tide could have swept away most of the dead matter. I regularly count the number of live LBBG and BHG present at this part of the Ria, which, during today’s upcoming tide, was surprisingly low, compared to earlier high tide visits. I have informed Biology student 'João' from the University of Aveiro about this situation in the hopes that the situation can be investigated. Luis would inform his supervisors about this, what seems to be fair to call, gull die-off in the Ria de Aveiro.

Gull rings on a very early morning visit to Leixoes harbour, Porto (September 11)

About 8500 gulls were present, including 6000 Yellow-legged Gulls and 2500 Lesser Black-backed gulls. Between 05:45 – 09:00 19 colour-rings were read (14 LBBG and 5 YLG).

There are some things more interesting than gulls. 06:53AM: Adult Peregrine Falcon Falco peregrinus consuming its breakfast at one of the two main cranes in the container terminal of the Leixoes harbour.

Gull rings at the Eirol landfill, Portugal. August 28, 2013

On August 28, 41 rings were read at the Eirol landfill. Starting time 7:15 and working until 13:00, under an unbearable sun. A good number of gulls were present at arrival to the site. Although many more were arriving within the following 2-3 hours, the same amount of birds departed to a nearby lake and some back to the NW, the Ria de Aveiro and nearby beaches.  I’d guess that in total there were fewer birds present than during my previous visit on 21-8, roughly 4200.

I would expect there to be more birds by now, as LBBG migration currently is well on its way, so this surprised me a little. There might be a chance that the amount of exposed waste and the amount of waste disposed at the pit has become a limiting factor for the birds. A large part of the open dump has been covered with sand recently. Fyi:  I don’t mind this. To me it’s one of the interesting factors involved in following bird populations at their main artificial food supply.

LBBG rings were applied in Guernsey (16), Great Britain (9, excluding Paul Veron’s Guerney Gulls), The Netherlands (6), France (4), Belgium (2), Germany (1), Denmark (1) and Spain (1). The only ringed YLG that I could find was ringed in Spain.

A fresh start at the Eirol landfill near Aveiro, Portugal

Today, August 21 2013, during a morning visit to the Eirol landfill near Aveiro, Portugal, 36 gull-rings were read. The number of gulls was still relatively low, I suspect about 6500, including about 6100 Lesser Black-backed Gulls, 400 Yellow-legged Gulls and only a few Black-headed Gulls. The number of white storks was impressive: well over 1000 took off and left the site around noon.

 

The only colour-ringed Yellow-legged Gull observed today.

Probably the first recorded Audouin's Gull Ichthyaetus audouinii in Eirol

In between foraging trips, the birds sleep, take a bath, preen their feathers or read a magazine

Dirty, but readable ring. One of many from Paul Veron (Guernsey)

These are not gulls, but White Storks

Around noon it became too hot for me and the gulls. Only a few hundred were still present when I left the site.

Beachcombing @ Rottumeroog, The Netherlands