Rain, ducks & other matters at the São Jacinto reserve (October 1 - 4)

This four-day stay at the Sao Jacinto reserve included two days of duck captures. However, only on our second day of trapping did we manage to catch some ducks, as with our first attempt our traps remained empty. This was possibly caused by recent disturbance of an unknown kind near our catching site. With fall migration on its way, the diversity in the duck species is increasing rapidly. Besides the usual Mallards, there is now a good number of Eurasian Teals present, as well Eurasian Wigeons and about a dozen Shovelers and Gadwalls. In the end we managed to catch and mark a reasonable number of Mallards and four teals, of which two teals were actively moulting primaries in our pond. And as autumn has arrived we also received A LOT of rain, raising the water level at the pond with several centimeters during our stay. On the fourth and final day we got some attention from national media. Two reporters from SIC television visited us for a news report about the duck work in Sao Jacinto. In the morning their visit got delayed due to massive rainfall, but in the end it all worked out it seemed and we could proudly present some of our captures on national televion. The item got aired on October 12 but can still be viewed here:

http://sicnoticias.sapo.pt/pais/2013/10/12/mais-de-20-mil-aves-foram-marcadas-nos-ultimos-20-anos-em-portugal

Northern Shoveler Anas clypeata

 

One of the 14 Gadwalls Anas strepera that were present had been marked a few years earlier.

My favorite Eurasian Teal V/Y/V appeared again for the first time after being away for the entire summer. One of six marked teals that we resighted.

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.