Population dynamics of two beaver species in Finland
​Eurasian beaver (Wikipedia)


In our paper, we used information on winter lodges collected by volunteers throughout the country. This is so-called citizen science data. Such data collection is really exciting to researchers because it allows studying phenomena on larger spatial scales than usually possible if the data was to be collected by a researcher or research group. For beaver monitoring in Finland, hunters report every third year the number of winter lodges in the area of their hunting association. We grouped the reported winter lodges per municipality in Finland to obtain counts of winter lodges every third year from 1995 to 2013. Each hunting association covers some 2000 – 10 000 ha and there are hence many hunting associations in each of Finland’s municipalities.


Ecosphere Volume 8, Issue 9, 14 SEP 2017 DOI: 10.1002/ecs2.1947
Municipalities in Finland where citizens counted beaver winter lodges. Red is the North American and light blue the European beaver. Grey land area holds no beavers. Darker blue is sea.

Model approach

By grouping hunting associations within a municipality, we were able to construct a measure of reporting intensity (number of hunting associations in a municipality that filed a report). As is common to citizen science data, reporting is never complete as volunteers are not paid researchers or field technicians following a specific design all the way through. Clearly, as more reports are filed in a municipality, a larger fraction of all beaver winter lodges “out there” will be reported. As reporting intensity varies over time and across municipalities we need an approach that can handle observation data while also correcting for heterogeneity in reporting intensity. We therefore used a recently developed model approach which is based on time series of counts obtained at many sites to construct the population changes over time, while correcting for reporting intensity.


Our main finding is that North American beaver numbers are declining in Finland and Eurasian beaver numbers are increasing, which is clearly a sign that current management of these species is working! Nevertheless, according to model estimates of the number of winter lodges, North American beavers (6000 winter lodges) are still more abundant and widespread than Eurasian beavers (2000 winter lodges). An interesting finding was that the abundance of North American beavers was higher in municipalities closer to where the species was introduced 60 years ago. On average reporting intensity was pretty low; the model estimates indicate that from 20% to 30% of winter lodges are reported.


The monitoring of beavers in Finland will continue. Latest count was carried out in 2016. Modern phone-based applications (apps) will likely play a key role in getting volunteers to more readily report where they see a winter lodge. These are exciting times for citizen science.
Jon Brommer
Riikka Alakoski
Vesa Selonen
Kaarina Kauhala