The other day a friend was telling me about a recent encounter with some harvest mice, his first sighting of these overlooked mammals in thirty-odd years of watching wildlife. Two of these tiny creatures were clinging to some reeds in an area that had been inundated with floodwater and he was struck by their small size and by the delicate way in which they used their tails to secure their hold on the reeds.
The harvest mouse is a mammal that I know well, having once kept and successfully bred them in captivity. They are amazing creatures, far more delicate than their larger relatives (like wood mouse, which I have also kept in captivity) and with a lot of charisma. It is difficult to know how common they are across the county, their small size and arboreal habits make them difficult to trap using conventional live traps, and I suspect that they are easily overlooked. Most records will either come from cat owners, whose pet has delivered an unfortunate harvest mouse to its owner, or from those who encounter the cricket ball-sized nest in a field margin or reedbed setting. Other records come from the pellets cast by hunting owls.
At this time of the year harvest mice may still be giving birth, the first births beginning in late June and the last extending into October or beyond. Cold wet weather at this time of the year can be a particular problem. The nest into which the young are born is up to 10cm across and woven into the vegetation. The young mice will use the nest for 2-3 weeks, the female abandoning them at 16 days if she is pregnant with her next litter, and the nest then becomes increasingly battered as the youngsters explore their growing world and gain independence.
I used to find harvest mice would enter my live traps, set for field voles on a wet meadow, from November through into March, suggesting that at this time of the year they spent more time on the ground. It was always a thrill to see the russet-orange of a harvest mouse drop into the polythene bag into which I emptied the contents of any trap that had been triggered. Once released on a stem their agility could be appreciated and, if I sat very still, they would sometimes sit and groom, balanced by tail and a single foot alongside the vertical tube of plant stem. It was these encounters that probably made the harvest mouse my favourite mammal, topping even the dormice that I had studied in Sussex several decades ago. It’s been a while since I saw a harvest mouse so maybe I should go looking for one.