This autumn I am doing field work in Falsterbo. Falsterbo is the most south-western tip of Sweden. It is one of the most important strategic bird migration sites in Europe. But what does this mean and why is this?
When migrating, birds usually avoid flying over huge water bodies, desserts or mountains. These habitats are ecological barriers for them and crossing them can cost a lot of energy or be even deadly. Birds that can not land on water (like all of your garden birds) try to avoid crossing big waters as long as they can. If they hit strong winds or rain while flying over sea, this could be their end. So better avoid as long as you can.
The Baltic Sea is such an ecological barrier. Migratory birds leaving Scandinavia in autumn and flying southwards to their wintering areas in either southern Europe or Africa, fly through Sweden. When they hit the coastline, they follow it in south-westerly directions as long as they can. At some point they reach Falsterbo, the south-western tip of Sweden, where the birds end up like in a funnel. At this bottleneck they are forced to cross the Baltic if they want to continue migrating. Many millions of birds pass Falsterbo every autumn on their migratory journey. It is an astonishing place to watch bird migration, one of the best in Europe. You can stand at the very tip of Sweden and at good days several 10.000s or even 100.000s of birds are flying over your head. A very breath-taking experience.
Such a place is not only great to enjoy bird migration. A migratory bottleneck like Falsterbo, where each autumn millions of birds pass, is also an excellent place to study birds and bird migration. For example, if you tell or catch migrants each year and you do that for many years with the same method, then you can monitor populations. That means you get an idea if the population of a particular species growth, is stable or declines. In Falsterbo each autumn one or two ornithologists count the migrating birds. They do this every year with the same method. Starting at 11 August and continuing until 20 November. They do this every day staring at about 30 minutes before sunrise and continue till 14.00 o’clock; independently of weather conditions! These standardised counts started in 1973 and by now a long-term dataset is available. It shows that some species have increased a lot in this period, other have decreased a lot. The value of such long-term datasets is enormous.
Another method is standardised catching. In the lighthouse garden at Falsterbo a standardised ringing scheme is operating since 1980. From 21 July to 10 November every morning just before twilight nets are opened to catch and ring birds. This also allows you to monitor population trends, but also study many other things (I will come back to this later). Counting and ringing complement each other perfectly. During the counts you can obviously count only the birds migrating at daytime. But some species migrate (exclusively) at night time. These (and resting day time migrants) you can catch when they rest in bushes like in the lighthouse garden.
To study stopover duration and departure decisions, CanMove has a sophisticated radio-telemetry system at the Falsterbo peninsula. Antennas are placed on different locations and they can pick up signals from radio-transmitters. Radio-transmitters are very tiny tracking devices that you can up on a bird. They send a signal and with an antenna you can pick up the signal and determine the direction of the signal. The antennas of the different locations are connected with each other via a wireless network; and they are synchronised.
An automated system is scanning non-stop for transmitters. Analysing all data you can determine by triangulation where the transmitter (and thus the bird that carries it) is. When you put transmitter on migrants resting e.g. in the lighthouse garden, you can find out how long they stay, at what time of the day they depart and in which direction they fly. My colleague Sissel has done this for the past years as part of her PhD thesis and produced very exciting results. In the coming weeks I will do similar things and will try to answer some of the questions that emerged from Sissel’s work. If you want to know what exactly I will be doing, then watch out for the coming posts!