They say there is no such thing as bad weather, just inappropriate clothing. This might apply to humans but if you're a bird, you've simply got what you've got. Give or take the odd feather, birds have pretty much the same 'outfit' for the entire winter season. Given their lack of choice in attire, you may well have wondered how they survive the elements when those elements get feisty.
They can, and they do (mostly) by adopting various avoidance strategies and mixing these behavioural changes with a few physiological tricks. If a bird can't feed or finds itself exposed in some way, the options are to move, seek shelter, and/or conserve energy, and they do this in various ways.
Firstly, avoidance.There is some evidence that birds can detect big storms and extreme weather in advance. Studies have suggested that some species can detect the low-frequency infrasound and low air pressure that storms create long before they hit. The result is that they can act by leaving the area.
When the weather is wet, windy, cold, or, as is often the case, all three, birds' main challenge is finding food, which requires much more energy.
The obvious solution (from the point of view of a land-based mammal) would be to store fat—for its insulative properties and as an energy store.
Compared with mammals, birds can't put on loads of fat to see them through hard times - but they can put on some. The issue is one of compromise… too much fat, and the bird's ability to fly and avoid predators is reduced; too little, and they may run out of 'juice' during a very cold or severe weather event and perish.
It has been shown that as atmospheric pressure drops before a storm, birds will increase their time foraging for food - with 85% of the daylight hours dedicated to hunting for food already, there is not much wiggle room - the race against time is on. Fat birds might not fly, but they do weather the storm better.
Small birds such as tits are only able to lay down enough fat to get them through a night; something like 10% of a bird's body mass in fat is needed every day (even smaller birds like Goldcrest, this requirement goes up to 30% of their body mass!).
A calorie per gram of body weight doesn't sound like much, but when this totals around 10 g of invertebrates, almost the body weight of the bird (a blue tit weighs in at around 11g), that's over 300 or so individual bugs. You can start to see how their lives might hang in the balance if the weather hinders their foraging.
One very neat trick is that while you're tucked up in bed maintaining your 37°C body temperature the small birds roosting outside your window can't afford that luxury, so they use something called nocturnal facultative hypothermia.
In doing so, they can deliberately drop their body temperature from their active temperature of 42°C to around 35°C or lower. A massive energy bill saving and one that increases the chances of a small bird surviving the winter weather by over 50%.
So you can start to understand some of the issues when the weather turns nasty. It doesn't matter if it's Sub-zero or just wet and windy; the outcome is the same.
Either there is too little food to be found, or the cost of getting it is greater than the energy gained when it is found. The juice is just not worth the squeeze, and so they seek shelter.
Large birds of prey and some chunkier waterfowl can simply sit it out for a bit. A larger volume-to-surface area ratio means less area to lose body heat over, and they can carry a bit more bulk, too. But even the toughest birds can fall foul of the most extreme weather. A walk along an exposed seashore after big storms at sea will often reveal the sad and soggy bodies of sea birds.
Feathers are critical; they are both a bird's shell layer and the thermals. They work like this; the contour feathers overlap, like tiles on a roof, forming a continuous protective but flexible layer of protection against the elements.
When a bird preens, it is zipping back together any barbules that have become disengaged and smearing a coating of a fine waxy substance produced by the preen gland at the base of the tail. Along with foraging for food, preening is the most important activity for a bird in the winter, with some birds spending over 10% of their day performing this essential maintenance.
Beneath the contour feathers are the down feathers, which are just as important. The barbules of these are loose and fluffy, designed to trap pockets of warm air against the skin. Small birds will often grow fluffier down feathers or add more semi-plumes to their plumage during the autumn, a physiological anticipation to buffer their bodies against the cold.
One study found that house sparrows' total feather mass increases by 70% in readiness for the winter! Fluffing up is an obvious behaviour linked to all of this extra down; by lifting the feathers, more insulating air is trapped against the bird's body, making it, in effect, a living down jacket.
When the wind and rain hit, birds fly less—this may not be such a bad idea. Low atmospheric pressure or moist conditions make flying less efficient anyway, and so, if they can help it, they try not to fly as a way of preserving energy. (This is why disturbing bird roosts and forcing them to take to the wing can have large negative consequences.)
After that, it is simply a case of finding shelter. Hunkering down, getting out of the wind, in the garden context, often involves simply getting on the leeward side of a hedge, building, or tree trunk, but for some species, other man-made spaces such as outbuildings will do.
Finding shelter is all very good for birds living in habitats that offer some structure, but what about those of open habitats? At this time of year, sitting on the edge of mudflats, the same rules apply, but the birds that congregate at the high tide roosts have next to nothing to block exposure to the wind. But watch them….
They're all facing the same direction - into the wind. Of course, this makes sense for any bird - the wind smooths the feathers in the direction they lay on the bird's body. Anytime a bird's feathers become ruffled, they lose some of that warm air layer trapped underneath - like when you accidentally let cold air in under your duvet! They will also huddle in tight groups, those on the outside of the group constantly jiggling around. Over time, they all 'do time' in the wind, forming a living and continuously circulating windbreak.
Even the non-feathered parts of a bird have neat and unseen adaptations beyond the obvious one of standing on one leg.
On a recent bird-watching trip to the coast, I noted a Sanderling on one leg - however, in the entire 20 minutes we watched it, not once did it put the leg down - it just pogoed around, even while feeding and preening to the point I was sure the bird had one leg. Then it joined the rest of the flock - they were all at it. It makes sense if you think about it; with only one of 2 legs exposed to the cold, wet mud - your heat loss (and therefore energy lost) is halved.
The best bird adaptation is an internal one, though. It's something called a counter-current exchange system. At the top of a bird's leg, blood vessels containing warm blood leaving the body for the legs pass close to blood vessels containing cool blood returning in the opposite direction towards the bird's' red hot core'. The effect is that little heat is wasted; it is exchanged with the warm blood, heating the cool blood. Neat.
But you can help many terrestrial species, especially those in the garden, not just by supplying food from clean feeders, but in other more sustainable and long-term ways.
Invest in bird-friendly planting, and consider the space you've got and how exposed it is to the prevailing wind direction (in the UK, this is almost always from the southwest).
The clever planting of hedging (native is best) can create a living windbreak, taking the teeth out of any gale and providing shelter immediately behind and creating some structure in which birds can roost. If it is a native species (I like a Holly, Hawthorn, yew or Ivy - you've got all-around interest not just for yourself but the flowers provide nectar for pollinating insects, and the leaves are salad for smaller invertebrates, which in turn are predated on by most species of garden bird to feed their young in the summer ( bugs = the building blocks for making baby birds!) Then there are the fruits produced at the end of the year, which fuel many species just when they need a boost of calories prior to migration or moulting.
Think about trees too - if you have the space (Rowan is a good wildlife-friendly small tree for smaller spaces) or a bare wall, these can always be improved by planting climbing plants. Honeysuckle, climbing hydrangea, pyracantha, cotoneaster and Ivy all work well. When well managed, these will not harm the masonry - in fact, the same effect it gives to sheltering birds will work in your favour too - it has been proven that vegetation planted on or close to your house will help with the energy bill of not just the birds but yours too - saving on heating in the winter and air conditioning in the summer. It really is a win-win.
Just creating spaces, crevices, and hide-outs that are secure from predators, insulated from the worst of the weather and dry is a simple way of helping. Nest boxes are more than just somewhere for birds to rear a clutch; they are often put to good use 'out of season' too; you could also put up 'bird pouches'. Many small garden birds, from tits, dunnocks and wrens, will utilise them in very cold, wet weather.
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