It's been very cold in Florida so far this winter, where three of the reports are from. Cold in the eastern half of the US, and some of these reports are from Arkansas and Lousiana which were swept by cold fronts. And some are from the UK, which has had a brutally cold winter, and from elsewhere in Europe, which also has had a cold winter.
There are ample news reports to support the conclusion that many of these kills could be caused by cold weather. Occam's razor is the best approach when evaluating such events.