The previous reports I can recall were near the arctic, where these die offs are common because of weather. For example, 75% of the north American musk ox population starved one recent year because of rain that later froze and made a barrier preventing the oxen from feeding. Or storms that kill huge numbers of birds.
Farther south the fall red tides wil kill many fish.
Other fish kill reports I can recall were all related to chemical spills or farm runoff.
Rabbits and grouse have their mysterious population cycles, but no body is comparing these recent events to such cycles.
These latest reports are not consistent with anything I have previously read or experienced.
If it is true that these die offs are common, then let's see some credible documentation of previous recent such events. What, for example happened like this last year? And the year before? Simply saying these are common is insufficient as a credible argument.