Sweden : Roundup of 2023 expedition

Update from our Sweden bear volunteer project

The inaugural expedition in 2019 visited 28 bear den sites and mapped 24, found 10 scats at 15 bear cluster sites, recovered a bear skeleton from a bog for further analysis, recovered a valuable transmitter, covered over 2,000 km of the study site, had two bear encounters and several with moose, capercaillie and other interesting wildlife, increased the scientist’s bear den database by between a third and a half, and in one short week gathered scats worth six weeks. The expedition scientist called the expedition’s contribution “invaluable”.

The post-Covid second and third expeditions (2022 and 2023) built on the successes of the first expedition by collecting a significant amount of up-to-date data on the bears’ winter dens, day bed sites and their scats. Following a review, the length of expeditions was increased from 2023 to maximise data collection time. This resulted in the 2023 expedition visiting 68 sites, including 38 winter dens and 35 scat collections, ten of which were ‘first scats of the season’ (especially valuable samples that can reveal what a bear has eaten before and during hibernation).

We thank all citizen scientists very much for their help. An expedition report has ben published once data were analysed and here is its abstract:

From 27 May to 4 June 2023, eight citizen scientists collected data on bear denning behaviour and feeding ecology by investigating the 2022/2023 hibernation season den sites of GPS-collared brown bears and by collecting fresh scats from day bed sites. 2023 was the third year of Biosphere Expeditions citizen scientists assisting the Scandinavian Brown Bear Research Project (SBBRP) after 2019 (followed by an enforced COVID-19-related break in 2020 and 2021) and 2022. It was the first year when field sampling was extended by two days to a total expedition length of ten days.

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 training, citizen scientists were divided into three to four sub-teams each day for seven days of field work. On field work days, citizen scientists were given locations where collar data suggested that bears had spent significant time either denning or around a kill site. Citizen scientists then went to those locations and 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 found at those locations were also collected, and the habitat type around the den and the visibility of the den site were described.

In a very significant contribution to the SBBRP’s field work, the expedition visited 43 winter positions and investigated 37 dens of 30 bears, which represents about 75% of all winter positions that the SBBRP recorded in 2022. Previous expeditions investigated 34% (2019) and 50% (2022) of all winter positions recorded. The significant 2023 expedition increase is due to the extra two field days introduced with this expedition. Additionally, the expedition collected 100% of scat samples that the SBBRP normally collects during a research season. Previous expeditions collected 50% (2019) and 100% (2022).

As in 2022, two bears shifted their dens at least once during the hibernation season. In total, the expedition found 37 dens; five soil dens, eleven anthill dens, four anthill/soil dens, seven stone/rock den, five dens under uprooted trees and five basket dens. Unusually again, as in 2022, one pregnant female that gave birth to three cubs during winter, and one female 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 0.7 m. The entrance on average comprised 16% of the open area. The inner length of the den was on average 1.4 m and the inner width was 1.3 m. The inner height of the dens was on average 0.7 m. Bears that hibernated in covered dens used mainly mosses (43%), field layer shrubs (21%) and branches (22%) 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 mosses (64%) followed by grass (17%); and field shrubs (17%) as nest material. The expedition found ten first post-hibernation bear scats at the den sites.

Twenty-seven bears selected their den sites in older forests, and three bears in younger forests. The habitat around the dens was dominated by spruce (Picea abies) 39%, scots pine (Pinus sylvestris) 36% and birch (Betula pendula, Betula pubescens) 26%.

The SBBRP is very thankful for Biosphere Expeditions’ significant annual data collection aiding its long-term study of brown bears. With the help of these data, three reports and publications are on course to be published within the next two years: (1) A global review of the factors influencing den types of brown bears, (2) a brown bear dietary specialisation Master thesis based on faecal samples and (3) a publication on the effect of den type on hibernation duration and reproductive success.

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This rounds up this expedition and here are some feedback videos and a picture gallery of the expedition:

Sweden bear conservation holiday update