Massive numbers of starlings are dying: no clear cause

Around the end of October and early part of November, dozens of dead starlings were found underneath the trees around the Huygenspark in The Hague for several days. The animal ambulance ‘The Hague’  and bird sanctuary ‘De Wulp’ collected around 300 dead starlings. A few of these were post-mortem examined at the DWHC1.

No Usutu virus or rat poison

The examination showed that the starlings had a good body condition, some even had sufficient fat reserves. The starlings had extensive haemorrhage in the body cavity and cranium, enlarged liver and spleen and the stomachs were empty and some were purple coloured. A few starlings had microscopically a mild hepatitis. It is still unclear what the cause of the abnormalities was. The haemorrhage might have been caused by falling out of the tree onto the ground. The testing for avian influenza, carried out by WBVR2, was negative. The testing for West Nile virus and Usutu virus, carried out by Erasmus MC3, was also negative. There is still ongoing research for other viruses. The starlings were also tested for presence of rat poison. These tests were also negative.

Even though the cause of death is haemorrhage due to trauma, it is still unknown what caused this trauma. So a clear cause for the mass mortality is still unknown, but a few things could be excluded.

1 = Dutch Wildlife Health Centre
2 = Wageningen Bioveterinary Research
3 = Erasmus Medical Centre