Usually seasons are announced by the arrival of things - snowdrops, swallows, falling leaves, shortening days and the like. These can be dated and years compared by the date the first blackbird sang or first swallow arrived.

Sometimes though seasons are noted by the absence of things with which they were once associated. Of these the most notable is the cuckoo, an April regular during my childhood but not heard round here for many years now.

Another of these is clover, once commonplace but now much less so, and coltsfoot which was everywhere but not been seen for ages either. Ragwort is still common but cinnabar moth caterpillars have declined.

I have no data to back these up, just my reflections. But I haven’t heard a cuckoo round here for years.