I SPY EVOLUTION
It’s a new year. Welcome to 2025. Perhaps you’ve made some resolutions. Perhaps you’ve even kept them thus far into the year. If so, good for you. If not, don’t beat yourself up about it. You have the entire rest of your life to make yourself a better person, not just the first few days of the new year.
Have the birds made any resolutions? Of course not. They don’t know that it’s a new year. They don’t have a calendar, except for the internal one relating to the changing of the seasons. At a base level, their lives are no different today than they were yesterday, or last week or even last year.
A bird’s day.
That’s about it really. That’s all there is to their lives in the winter, survival. The breeding season brings a whole lot of different priorities but I’ll talk about those when the time comes. In the darker and colder months it’s all about keeping going and building up enough strength and conditioning for the upcoming mating rituals, breeding and bringing up babies.
A bird’s day rarely changes, but over a few generations there are amendments that can only be seen with the benefit of human hindsight. I’ve told my Chiffchaff story many times to visitors at the RSPB Old Moor welcome shed. If you’ve heard it before I apologise but it’s worth repeating and I have a few updates to it. Let’s go.
When I was a lad just about every Chiffchaff in Britain packed its bags as soon as the first chill winds blew, from late August onwards. They aren’t particularly hardy chaps so they bobbied off every year in search of winter sun. They mostly headed for Southern Spain and Northern Africa which is an incredible distance for such a tiny bird. My old bird guides, inherited from my dad and his dad before him, said that Chiffchaffs were uncommon visitors to Southern England during spring and summer. That was then. Nowadays you can find them throughout England and even into Scotland during warmer weather and quite a few will spend their entire lives on our British Isles.
Around a thousand plucky little birds won’t even start to make that long southern flight. They’ll stay here all year long. These birds have developed an adequate resistance to the cold of our British winter. That number of individuals doesn’t seem many but it’s a reasonable percentage of our small population of this noisy little bird, and the numbers staying all through the calendar are rising every year.
In my head our winters are white over, deep and crisp and even. Some days I even expect that I’ll get my big coat out. Of course 21st century winters are nowhere near as harsh as those of my youth. The truth hit me hard the other day when a weather forecaster said, “It’s going to be eight degrees over most of Yorkshire today. That’s about average for this time of year.” What she meant of course was that it was around an average December temperature for the 21st century. My head is still stuck in the mid to late 20th when it was sub-zero for weeks on end and we expected large amounts of snow that would hang around for a month or more. We expected, and the north wind delivered but since then the world has changed but I haven’t changed with it. Those days of Christmas card vistas are gone, probably for good, and the Chiffchaffs have adapted even if I haven’t.
Some of ‘our’ winter Chiffchaffs are from up north in Scandinavia. They start their journey southwards at the end of their summer but when they hit the relative warmth of coastal or Southern England a few of them realise that it’s actually warm enough for them to spend the winter here. They don’t need to continue much further southwards on a dangerous journey when we can provide them with all that they need to survive the (relatively) colder months.
We are seeing Blackcaps here over the winter months more and more too. I’ve seen one regularly in front of my Old Moor Welcome Shed over the last few weeks. Cetti’s and Willow Warblers, Whitethroats and Wheatears are all showing signs of migratory reluctance too. Even Swallows and House Martins are leaving Britain later and later each year. We can expect those numbers of individuals and species to grow if our planet continues to warm.
And at the other end of the temperature scale, we have birds like Waxwings who are finding that their Russian, Icelandic and North European winter homes are warm enough that they don’t need to fly to Britain for Christmas. Bewick and Whooper Swans too. It’s exactly the same pattern as the songbirds, just moved a little higher up the globe.
Climate change is a big driver of this change to birds’ behaviour, like so many others. You and I have played our part too, with the huge number of bird feeders in British gardens making food available in these parts that simply wasn’t available to previous generations of migratory songbirds. This is nice for us as we get to see some pretty birdies in our gardens, woodlands and nature reserves in winter where our forefathers wouldn’t have had the chance but it has irrefutably changed their migratory patterns.
And here comes the shocking headline news. When these overwintering birds have been caught, ringed, measured and released it’s been found that their wings are actually becoming shorter than those of their ancestors. I always used to associate evolution with dinosaurs and time spans of millions of years. That’s true in some cases but it’s going on here too. The shortening of these birds’ flight feathers is evolution while we watch. They don’t need big, strong wing muscles and feathers if they aren’t going to make a two-thousand mile journey twice a year. That’s the distance from London to Cairo in Egypt, a typical Chiffchaff migration flight. So if they can save that energy by not growing those stronger wings, they can put it into general fitness to increase their survival rate and make them more attractive to a mate. And if you were a migratory bird coming back to these parts to breed, you’d be absolutely shattered from that exhausting flight. If you looked at a bird who’d not made that trip and he or she was much fitter, better looking and more attractive to a prospective partner than tatty old you, wouldn’t you think twice before setting off next year?
But what if we had just one throwback winter? Weather occasionally does this. We’ll have a ridiculously wet spring once in a while or an especially windy autumn. What if, just once in the near future, we have a shockingly cold winter with snow covering the country and temperatures below zero? It’s happened before, there’s no reason that it couldn’t happen again. It’s unlikely, yes, but it’s not impossible.
Well if that were to happen it would be absolutely devastating for those little birds that have evolved to stay here in our green (or snow white) and pleasant land. They simply wouldn’t be able to survive the drop in temperature and lack of available food. Most of them wouldn’t make it.
Can we reverse this trend? Possible, by doing all we can to fight climate change and its effects on our planet. See the RSPB’s stance on the subject and what it - and you - can do at this link.
In the meantime, try to keep track of the bird species that you see change over the coming year. Who comes in, who moves out. It’s a lifetime’s study.
See my weekly RSPB Old Moor blog at "View From the Shed". I usually wear a big hat.