Sweden : 2022 expedition round-up

Update from our Sweden bear volunteer project

The 2022 Biosphere Expeditions citizen science expedition to Sweden to study brown bears together with Dr. Andrea Friebe of Björn & Vildmark and the Scandinavian Brown Bear Research Project has been a success for the second year running and overachieved on its aims.

In a nutshell, the expedition documented all 24 bear dens of the study site, collected over 100 bear scats, recorded 30 day beds, 8 carcasses and a multitude of other interesting events such as gnawed antlers, encounters with moose, fox, owls and other animals. Dr. Friebe now relies on this citizen science contributions each year to conduct significant parts of her work on brown bear ecology in a changing world of climate change and forestry. In her words “essentially, if the expedition was not here to do this work, it would probably not get done” and the expedition is “a showcase of how citizen science can supplement existing research projects run by professional scientists”.

All this is in evidence in the post-expedition scientific report (abstract below). The 2023 expedition has been lengthened to 10 days to be able to achieve even more and Biosphere Expeditions looks forward to returning to Sweden in May/June 2023.

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Abstract of the 2022 expedition report

This is a report about the second year of collaboration between Biosphere Expeditions and Björn & Vildmark with the overall purpose of researching the behaviour of free ranging brown bears (Ursus arctos) in central Sweden for the Scandinavian Brown Bear Research Project (SBBRP). This collaboration investigates, amongst other topics, how climate change as well as human activities affect the brown bear behaviour and population, and provides managers in Sweden with solid, science-based knowledge to manage brown bears.

From 28 May to 4 June 2022, six citizen scientists collected data on bear denning behaviour and feeding ecology by investigating the 2021/2022 hibernation season den sites of GPS-marked brown bears and by collecting fresh scats from day bed sites. All field work was performed in the northern boreal forest zone in Dalarna and Gävleborg counties, south-central Sweden, which is the southern study area of the SBBRP. After two days of field work training, citizen scientists were divided into three to four sub-teams each day. All study positions were provided by the expedition scientist and only data and samples from radio-marked bears with a VHF or GPS transmitter were collected.

Citizen scientists defined den types (anthill den, soil den, rock den, basket den or uprooted tree den), recorded bed material thickness, size and content, as well as all tracks and signs around the den sites to elucidate whether a female had given birth to cubs during hibernation. All first scats after hibernation and hair samples from the bed were collected, and the habitat type around the den and the visibility of the den site were described.

Twenty-six winter positions of 21 different bears were investigated. Two bears shifted their dens at least once during the hibernation season. In total, the expedition found 23 dens; two soil dens, eight anthill dens, one anthill/soil den, one stone/rock den, four dens under uprooted trees and seven basket dens. Unusually, one pregnant female that gave birth to three cubs during winter, and four females that hibernated together with dependent offspring spent the winter in basket dens. Normally basket dens are mainly used by large males.

Excavated bear dens had an average outer length of 2.0 m, an outer width of 2.2 m, and an outer height of 0.8 m. The entrance on average comprised 28% of the open area. The inner length of the den was on average 1.3 m and the inner width was 1.1 m. The inner height of the dens was on average 0.6 m. Bears that hibernated in covered dens used mainly mosses (47%), field layer shrubs (36%) and branches (14%) as nest material, which reflected the composition of the field layer and ground layer that was present at the den site. However, bears that hibernated in open dens such as basket dens, preferred branches (43%) followed by grass (26%); mosses (19%) and field shrubs (12%) as nest material. The expedition found two first post-hibernation bear scats at the den sites.

Ten bears selected their den sites in older forests, and eleven bears in younger forests, only two bears hibernated in very young forest. The habitat around the dens was dominated by spruce (Picea abies) 37%, scots pine (Pinus sylvestris) 35% and birch (Betula pendula, Betula pubescens) 27%.

As part of its intensive data collection activities, the expedition investigated about half of all winter den positions that the SBBRP recorded in 2021/2022 and collected 64 scats at cluster positions, which represents all scat samples that the SBBRP normally collects during a time period of 14 days. A detailed food item analysis will be performed in 2025 and the data will be published.

It appears that climate change is altering bear denning behaviour and may reduce food resources that bears need for fat production. Overharvesting (hunting) of bears and habitat destruction are the major reasons why brown bear populations have declined or have become fragmented in much of their range. In Scandinavia, human activity around den sites has been suggested as the main reason why bears abandon their dens. This can reduce the reproductive success of pregnant female brown bears and increases the chance of human/bear conflict. Understanding denning behaviour is critical for effective bear conservation. Further research is needed to determine whether good denning strategies help bears avoid being disturbed. Additionally, enclosed dens offer protection and insulation from inclement weather. A continued fragmentation of present bear ranges, inhibiting dispersal, together with an increasing bear population, might lead to bears denning closer to human activities than at present, thereby increasing human/bear conflict. The dens that were investigated by the expedition were visible from 22 m on average. Cover opportunities and terrain types not preferred by humans are thereby presumably important for bears that are denning relatively close to human activities, but further research needs to be done to validate this theory.

Through all of the above, the expedition made a very significant contribution to the SBBRP’s field work in a showcase of how citizen science can supplement existing research projects run by professional scientists.

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Some photo impressions of the 2022 expedition:

Sweden bear conservation holiday update