Last week I finished my work with wild birds for another winter. As part of our research, myself and my colleagues catch wild Blue and Great tits and use them as predators to test various aspects of our moth’s defensive strategies. As I’ve discussed before this is a challenging task (tiny birds do not make for the most cooperative collaborators), but this year we had bigger problems: climate change.
I frequently hear from Finns in my department that winters in Finland used to be colder and more snowy. It’s true that during both winters I have spent here we haven’t seen much snowfall until after Christmas (although there was a brief period this year when it seemed the snow was here to stay, before temperatures soared to +10 Celsius and it all melted). In fact this Christmas was one of the warmest on record. While I am always a little sceptical of people complaining that this years winter/summer is “the worst ever” (for example I strongly believe that summers in England have always been predominantly cold and wet, despite what some of my elders may claim), there is no denying that Finland is in no way exempt from increasing global temperatures. Its beautiful white winters are going to get shorter, the months of dreary grey sludge longer.
This is of course bad news for lovers of winter sports (dog sledging in particular seems to be suffering, hard to train your dogs when there’s only a couple of months a year, or less, they can work), but why is it bad for our birds? Well for two reasons, first the lack of snow cover is bad news for anything that overwinters in the soil (like our moth larvae). These creatures normally rely on a thick layer of snow to insulate them from the worst of the cold, as well as sudden changes in temperature. Less snow means fewer moths, and other insects, come the summer. A more immediate problem for us is catching. We work with the birds in the winter, not only because they are not breeding then, but also because we lure them into our traps using food. Peanuts, to be specific. When food is abundant they have no reason to come; we have to wait until the snow cover makes foraging difficult to attract them in any great numbers. The later the snow comes, the less time we have for our experiments, and as soon as the temperature starts to rise in spring they go into breeding mode. Have you ever tried to run an experiment with a bird that keeps trying to court its own reflection? It’s not ideal. Sudden temperature changes are also not good. This year the temperature dropped from above zero to -30 in a matter of weeks. Winter is already a difficult time for small birds, but extreme changes like that stretch them to breaking point. In the weeks after the drop we saw almost no birds at any of our feeding stations. Were they dead? Had the just moved elsewhere? Were they hiding somewhere? We don’t know, but one thing was for sure, they weren’t where we needed them.
It’s not just the winters that are causing trouble. You would think that warmer winters would also mean warmer summers, but the truth is the past two summers in Finland have also been disappointing. Crucially, while we have had warm periods both years, we’ve had two very cold midsummers. My first midsummer here in 2014 it snowed! This means that insect availability drops sharply at the very time the birds are trying to feed their chicks. Unsurprisingly, chick survival is lowered and fewer new birds join the population.
All this means we have fewer birds and less time to catch them. To combat this we have to catch birds from further afield, sometimes using mist-nets rather than traps. It also (frustratingly) means we simply cannot do as many experiments. We are already planning ahead for next winter. What we really need now is a good breeding season, but even that will not be enough to bring the population back to what it was just two years ago. Much of the forest surrounding our field station has been cut down to make way for new housing. Many of our nest boxes were cleared along with it. We are now working to replace those (partly by selling nest boxes cheaply to local residents) and set up new feeding sites. With some luck we can maintain a decent population of both Great and Blue tits in the area for years to come. I hope so. When I first moved to Finland it seemed like an untamed wilderness, but I now see just how heavily humans have impacted it’s wildlife, and how quickly said wildlife is disappearing. For example, in January 2014 I came to the field station for a visit before starting my postdoc. I remember the head technician complaining about the Willow tits always stealing peanuts from the traps as they “knew we didn’t want to catch them”. In my past two winters I have seen exactly one Willow tit at the traps. I hope it comes back. It can have all the peanuts it wants.