Naturalist

Mistletoe, flightless females, and caching

We humans retire to our warm houses in winter, but how do plants and animals cope? By the end of autumn in woodlands there is a huge amount of accumulated leaf litter, which is gradually broken down over time by fungi, insects, worms and slugs etc. This recycles nutrients from the leaves back into the soil. Deciduous trees shed their leaves in winter to survive cold weather. However, evergreen trees, such as Scots pine, yew and juniper, and shrubs like holly, ivy and mistletoe, retain their leaves; they avoid freezing by having toughened waterproof waxy leaves, and some of them bear berries in the winter. Conifers even have ‘antifreeze’ in their sap. Mistletoe and holly have separate male and female plants, and only the female plants produce berries. Mistletoe is a partial parasite and its main hosts are crab apple and lime, although it can also be found on sycamore, poplar and hawthorn. Its berries are much loved by Mistle thrushes to the exclusion of other birds, hence its name! The seed is surrounded by a layer of very sticky jelly, which resists digestion in the bird’s gut, and sticks to branches when the bird defecates.

The majority of moths in Britain overwinter either as caterpillars or as pupae. However, despite spells of cold weather, a few moths spend the winter as adults. The December Moth and the Winter Moth are both regularly in moth traps during December and January. Other moths flying at this time of year include the Mottled Umber, the Chestnut, and perhaps even a late November Moth or a Red-green Carpet. Winter Moths, and some others that fly in winter, have a most unusual adaptation – the female moth has very reduced wings and is completely flightless; she crawls up the trunk of a deciduous tree, often oak, and emits pheromones which attract the males. A few adult moths even hibernate – the Herald and Tissue Moths overwinter in caves, mines and tunnels, and occasionally in outhouses. In spring the caterpillars of the Winter Moth, which can be very abundant in woodlands, form the main diet of woodland birds such as Blue and Great Tits when feeding their young; in three weeks a pair of Blue Tits feed around 15,000 caterpillars to their young! Many birds migrate to the UK in late autumn from colder northerly climes. However, as winters become milder, some Arctic breeding wildfowl and waders are choosing to winter further north, and numbers wintering in Britain have declined. Some birds that previously migrated south of the Sahara are now spending less time in Africa, or even wintering in Europe; for instance, many White Storks now spend the winter in Spain, and more Blackcaps and Chiffchaffs winter here. Winter is also the time of year when some species of birds gather in large numbers to feed and roost; skeins of Arctic swans and geese, both inland and on the coast; and roosts of thrushes and finches in thick evergreen vegetation. On TV we have all seen spectacular starling murmurations, which may number millions, such as the one on the Somerset levels; these roosts may result in ‘information sharing’ for some species. Caching (or storing) behaviour is found widely in birds and mammals which hide food for use in winter. In my garden Coal and Marsh Tits visit the bird feeders every few minutes to collect and store sunflower seeds; jays gather thousands of acorns in September and October and bury them; amazingly they manage to relocate over half of them, but others are found by squirrels; kestrels and squirrels also cache food. In autumn moles collect hundreds of worms underground to act as a winter store; they disable them by biting the tip of their nose.

Recent studies have shown the benefits of spending time ‘in nature’. The effects of getting out for a walk include reduced blood pressure, an increase of the stress-reducing hormone cortisol, and easing of depression, particularly in winter when light levels are low. By the time you read this, COP26, the United Nations’ annual conference on climate change, will be over - let us hope and pray that world governments have agreed to take enough steps to drastically reduce emissions of CO2 over the next ten years.