Clare, that reminds me, something I've been thinking about for the last couple of days. Here in Hardanger, Norway, there's no blueberries at lower altitudes, following a record warm Winter with no snow since well before Easter. Grasping for explanations, I first blamed the mice, more numerous than ever because of the early Spring. Their gestation period is less than 4 weeks, so they multiply many, many times during a hot Spring and Summer like 2014. Either they ate all the berries, or the lack of snow was directly causing the lack of berries. I dunno. Higher up, there are lots of berries, even now in September. I met hikers who climbed the hills and mountains last week just to find blueberries.
I expect to find lots of minor and major collapses like these, whatever their causes, in the years to come, and I also expect a multitude of causes to accomplish even more dire collapses. At the moment, birds of prey are prosperous, though, and a wanderer must be careful not to rest for too long, as eagle wings are pretty soon audible nearby.