January 2017

Fieldfare (In this case in Northern Europe in Sweden)

The holly and the ivy when they are both full grown – provide many species with food and shelter.  Well I think I got the first part of the carol right.  At this time of year as the weather and the countryside become increasingly grey, evergreens like holly and ivy leave a welcome splash of colour.  This is particularly true of holly with its bright red berries.  The berries provide an obvious food source for wildlife and in January song-thrushes and blackbirds will gorge themselves on them at a time when other food sources are scarce.  There may well be an influx of their less well known cousins the fieldfares and redwings from northern Europe also taking advantage of the berries.  Ivy berries, though less conspicuous than holly (They are a rather attractive velvety black colour and smaller than holly berries) also provide a welcome energy source for many birds.  Ivy flowers quite late in the season and the small easily overlooked flower clusters provide nectar and pollen for many insects, not least the ivy bee* (Colletes hedera) which emerges late in the autumn to take advantage of these flowers.

Ivy Flower - 

In terms of providing shelter, ivy provides plenty of nesting sites for birds like the robin, dunnock and wren.  It provides a good tangle of stems with plenty of leaf cover and is usually growing over a good solid wall or fence that offers a bit of insulation and protection from the wind.  The holly too provides nesting sites for many birds.  The prickly leaves make it very difficult for ground-based predators to climb into.  I recommend that you don’t clear up dead holly leaves from beneath the tree as cats won’t go anywhere near it.  The fact that holly and ivy don’t lose their leaves in winter means that birds can build nests in early spring that would be otherwise exposed in a deciduous tree before its leaves have sprouted.

 Of course, there are animals other than birds that feed and take shelter in holly and ivy, not least of which is the holly leaf miner.  This is a species of fly that lays its eggs in the leaf.  When the eggs hatch the larva (maggot) eats the inside of the leaf between the tough outer layers.  This eventually pupates and emerges from the leaf as an adult fly – if all goes well, that is.  There are a couple of species of parasitic wasp that lay their eggs inside the larva which hatch and eat the larva from the inside.  It’s gruesome but the holly has indirectly provided food and shelter for yet more species.  And it doesn’t end there because birds like blue tits and great tits can get at the larvae before they emerge, to add yet more species to the list provided for by the tree.  Even though the holly bears the crown, the ivy isn’t left out as regards leaf miners.  The ivy leaf miner is a micro-moth larva which starts eating inside the leaf but when it is big enough to moult, it leaves the leaf and spins a cocoon outside.  The micro-moth is the small grey tortrix (Cnephasia incertana) which is a common species that we often find in the moth trap.  (It isn’t restricted to ivy; it mines several other plant species.)   The holly and the ivy each support only one species of leaf miner which, considering the large number of leaf miners, makes them quite a selective host.

Though the bark of most trees carries mosses and lichens, I don’t remember seeing lichens on the smooth bark of holly – hmmm,  more research required.

* The ivy bee was described as new to science as late as 1993 from specimens found in southern Europe.  It was first found in the UK in 2001.

December 2016

As I write this it is cold and windy and wet outside and it will be getting dark at about 4 o’clock.  My annual anger at putting the clocks back has subsided into mild irritability that is probably not far from my normal state.  So the question is, what happens to the natural world when it gets cold, wet and windy and the clocks go back?  Clearly the natural world has no interest in the clocks going back, and even if it could be explained to them, any animal would instantly see the logical flaws and think we were mad.  They are already aware, much more so than us, that the day length has dramatically changed, and for many the shorter days means less time foraging for food or prey.  For some, that will lead to starvation, especially for warm-blooded creatures with their high energy demands.  So in order to avoid starvation they must have a strategy.  There are three basic strategies that an animal can adopt – migrate, hibernate, or stay put.

Migration is a fairly obvious strategy – when you can’t get enough food in one place, move to somewhere that you can find food.  Such a strategy is not without its costs though.  Exhaustion, and adverse weather can make the trip hazardous, especially for young animals, even without the Mediterranean macho men and their shotguns.  Migratory birds may find that their predators also migrate – hobbies, the small hawks that prey on swallows and martins migrate at the same time. (The hobby – Falco subbuteo, had the table football game named after it.) But for those that make it, they can enjoy warm sunny days and plentiful food.  Migration is mostly for flying animals like birds and butterflies, and unlike the huge wildebeest migrations in Africa, the UK doesn’t have any land animals that migrate as far as I know, except for a relatively short upland to lowland movement.  One group of flying animals that don’t migrate are bats, which brings us to the next strategy.

Hibernation.  This involves finding somewhere sheltered, well insulated and dry, and then to go into a deep sleep, or state of torpor so that energy demands are kept to the absolute minimum.  For warm blooded animals this means slowing their breathing and heart rates and reducing body temperature and the exposed surface area of their bodies to a minimum.  The dormouse epitomizes this – curled up into a ball in a warm nest and looking unbearably cute.  Bats do the same, but they do it as a group so that only the ones outside the group are exposed to the cold.  Clearly some swapping of positions is required; otherwise the outside ones would die and leave the next layer exposed.  Hibernation also has its dangers, the torpid state means that should a predator discover the hibernaculum (posh word for cosy winter nest) there’s no chance to react. Hibernating insects are also prone to parasitic and fungal infections.

With all the risks involved in migration and hibernation, maybe staying put and braving the weather is a better option.  It’s an option that usually needs a bit of forward thinking.  During the autumn, nuts, seeds, and berries are usually plentiful and animals that are going to stay active during the winter tend to feed themselves up and build up an extra layer of fat, both as insulation and as an energy reserve when the available food gets scarce.  Yet another strategy would be to have a back-up plan.  Grey squirrels and jays can be seen collecting acorns in autumn, which they bury and mostly remember where they are buried so they can be dug up later.

Of course, each of these strategies is not available to every species, and the ‘chosen’ strategy has been honed over hundreds, if not thousands, of generations on the whetstone of evolution.  Swallows didn’t discover sub-Saharan Africa on a random day trip, their route and destination will have gradually changed as the landscape has changed and food resources and predators have become more or less plentiful.

Maybe as we spend our winter in centrally heated well-lit homes it is worth considering the wildlife outside day and night in all weathers, and maybe topping up the bird feeders, because it really does make a difference.