The Swedish wolverine project – ecology and conservation

Update from the field – spring 2010

During spring 2010 we have spent two months in the field studying factors that influence wolverine populations - especially resource availability for female wolverine and their interactions with lynx. We have also studied aspects of wolverine behaviour that are important to understand, to more efficiently find and count wolverine dens (the method managers use to monitor the population in Scandinavia). In addition, we have continued to monitor reproduction and survival of individuals to understand more about how and why the population varies in size.

Thanks to EAZA and other funders we are able to follow wolverines and lynx equipped with modern GPS-transmitters. This gives us very detailed information on their movement so that we can document the animals’ activities, such as where they have food resources, how they maintain territories and interactions among individuals.      

One important part of our study is to estimate the proportion of females that reproduce each year and why this vary between years and individuals. Most wolverine females are presumed to be pregnant and give birth to cubs in February. However, many of them lose their cubs early after birth. Thus, we can document the number of females that keep their cubs long enough that we can find their den. This spring we monitored 12 wolverine females that were 2 years or older. Five of these reproduced and kept their young long enough for us to detect that they were denning. This is quite normal as the average proportion of females reproducing each year is around 55%. Most females start reproducing when they are three or four years old. However, this spring was the first time that we documented that a 2-year old female had a den! She was observed with two cubs emerging from the den on 5^th May. The female is the granddaughter of one of the first females captured in the project. Thus, her cubs are the 4^th generation that we will monitor in this study!

During this spring we studied females’ movements and activities around dens, daybeds, carcasses and kill sites. We do this to understand more about food availability for different females and how this influences their activities. We also learn more about the differences in movement between females with a den and those without a den. This could help managers to find den sites and separate those from other activities. In early summer, we will visit the documented den sites and day beds to document signs that are visible on the different sites, which could further help managers identifying differences between den sites and other activity centres of wolverine females.

With the GPS-transmitters we use, we get plenty of interesting data on movements and social dynamics, which was impossible to see before. For example, this spring we have been able to follow the process when a female has taken over the territory of a neighbouring female. The female that is losing part of her territory is 13 years old, which is a high age for a wild wolverine. Maybe she is getting too old and weak to defend a large territory?

Our preliminary results show that wolverines to a large extent eat reindeer that have been killed by lynx, and they do so during all seasons of the year. Although the wolverines hunt reindeer by themselves, lynx killed reindeer make up a high proportion of the carcasses they utilize. In light of our previous studies showing that wolverine female reproduction is dependent on availability of carrion in winter, this suggest that the presence of lynx in an area can have positive effects on wolverine reproduction and be a relevant factor for the growth of wolverine populations. This information is very important for our understanding of what determines the size and distribution of the wolverine population.

Finally, you are welcome to visit our project’s website at www.wolverineproject.se