ESS Ecology

As autumn is upon us, and winter around the corner, would you rather hibernate or migrate? Are you already preserving fruits and chopping wood, or booking that Caribbean holiday?

Looking to the wildlife world, we see both strategies in action in autumn, relating as many processes do, to food (which of course equals energy) and the requirement to obtain enough food to survive the harsh British winter. Falling temperatures and lower light levels cue senescence for broadleaved trees. What we see as a brilliant display of autumn colours is the loss from leaves of green chlorophyll - in effect photosynthesis shutting down. As light periods shorten and frosts arrive, trees must hibernate (well they can't migrate!), they enter a dormant state with stalled growth and energy expensive leaves, fruit and nuts are shed, and which are liable to damage from frosts.

Lower food availability is one of many cues for those animals planning to migrate. By late September, summer bird visitors have returned to warmer climates, such as the swallows and swifts to Africa. Winter visitors have arrived from even colder places, including many waders and waterfowl from the Arctic. For animals without the mobility of flight however, migration to warmer climates is not possible.

Luckily for animals that will spend the winter here, the timing of senescence and ripening of fruit and nuts is different among different tree species. Therefore, autumn offers a staged food resource for animals looking to stock up for winter. For example, Jays are known to bury up to 4600 acorns during autumn - for later retrieval in the cold winter months. On Oak trees, acorns will develop late in the season, so early on Jays may also collect hazelnuts or beech seeds. Similarly to nuts, berries ripen on different plant species from late August and right through the winter - elder, hawthorn, birch, and holly all provide berries at different times, readily eaten by small wintering finches. Although wintering birds do not go into state of torpor or long sleep, which we commonly associate with "hibernation", these birds slow down their activity and avoid energy-expensive activities such as breeding. Do humans do the same in winter and slow down?

What about those animals that don't feed on plant material? For UK bats, all of which are insectivores, winter sees minimal insect activity and bats cannot obtain enough food. Therefore, UK bats hibernate until spring when insect activity increases with the onset of flowering. By now, bats in Scotland and northern England have mostly entered their hibernation roosts, with bats in southern parts of the country soon to follow. Badgers do not hibernate for a long period of time, but may spend multiple days in their setts during periods of very low food availability.

While in autumn we see slowing of wildlife activity, and some particular animals such as bats, Badgers and breeding birds are not generally surveyed by ecologists, other aspects of wildlife are more easily observed in the field and survey work can continue. For example, fungi, lichens and mosses are easier to discover without thick woodland foliage, as is overall woodland structure and the extent of evergreen shrubs, such as invasive rhododendron. When bracken fern dies off at the first sign of winter frosts, surveyors can more easily detect small woodland herbs, such as wood anemone and barren strawberry that have taken refuge amongst the bracken. As winter does draw near, use the opportunity to uncover some smaller woodland features yourself, and instead of hibernating, or migrating, enjoy the outdoors - with some hazelnuts and elderberries in your lunch box!

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