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.
