Such deaths are unusual at this time of year in Iceland and their cause is unknown. The widespread deaths of Kittiwakes cannot be attributed to bird flu, according to Brigitte Brugger of the Icelandic Food and Veterinary Authority (MAST). Samples from the birds analysed by MAST ruled out the illness. While bird flu is unlikely to be the cause, extreme weather may be a possible explanation.

May 2023 in Reykjavik, Iceland has been a month of gloom and rain, with a chance of breaking a 70-year-old "sunless" record and becoming the "least sunniest" fifth month of the year since measurements began, as well as potentially breaking the record for the rainiest May on record.