The average route is about ten kilometres long. There are 500 rounds in all and about one thousand counters, all keen bird observers. The detailed statistics thus collected contain systematic information about one hundred bird species. The counters also record other data, such as the temperature, the snow cover and the rowan berry yield. Signs of global warming The monitoring data also allow long-term studies of the winter population trends.
Birds are good indicators of climate change.
Deciduous trees become more common and coniferous trees decline. This means better conditions for animals which thrive in broad-leaved forests, and loss of habitat for species living in boreal taiga forests. Climate change is by no means an easy subject to study, because there are many factors simultane-ously affecting the size of bird populations. For instance, frequent cold winters have an immediate effect on the populations of some species. In the mid eighties Finland had three cold winters in a row, but there were very mild periods towards the end of the nineties.