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No. 258: Wolves (Canis lupus) in Denmark, 2012-2017. Review and analysis of available population information

Sunde, P. & Olsen, K. 2018. Ulve (Canis lupus) i Danmark 2012-2017. Oversigt og analyse af tilgængelig bestandsinformation. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 52 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 258. http://dce2.au.dk/pub/SR258.pdf

Summary

This report provides an overview and analysis of the currently available information on the status, distribution and abundance of the wolf population in Denmark 2012-17, following the SCALP criteria. From a population perspective, the report covers the period from the first verified wolf observation in Denmark in modern times, 14 October 2012, until the first documented case of successful reproduction in 2017. Data originate from the Danish Wolf Atlas, a database established in 2016 and made partially publically accessible online (“www.ulveatlas.dk”) in September 2017. From June 2016 onwards, all new recorded observations were registered, treated and assessed following the methods used by the German wolf monitoring scheme and areas suspected to host wolves were surveyed systematically using systematic searches for scats and deployment of wildlife cameras. Data registered before June 2016 were evaluated retrospectively, observations were only added to the database if they fulfilled SCALP criteria. Because the registration and documentation procedures were only partially developed before 2016, the number of wolf occurrences and individuals identified from genotyped DNA-samples should be considered as minimum estimates, especially during 2012-15.

From 14 October 2012 to 31 December 2017, 167 verified (C1-level under the SCALP system) wolf observations were registered, providing evidence for seven genotyped individuals, which originated from Germany, and eight juveniles from the first Danish litter born in 2017. Based on the spatio-temporal distribution of observations, at least one additional individual could potentially be identified as not being one of these wolves, resulting in a minimum of eight immigrants in total.

All seven genotyped immigrants (five males, one female, one of unknown sex) originated from the Central-European lowland population. Six of these could be identified as originating from identified packs in Germany, 450-850 km from their Danish observation sites, and five (including the individual whose birth pack could not be identified) were registered in Schleswig-Holstein (the northernmost German federal state bordering to Denmark) 0.5-13 months prior to appearing in Denmark.

The first genotyped individual (GW051m) was found dead (diseased) a month after being observed for the first time in October 2012. The second (GW473m) and third (GW373m) individual were recorded multiple times in the same area in central Jutland, but during each of their respective active observation periods (February 2013-August 2014 and July 2015-August 2016, respectively) both appeared to have established stable home ranges. The fourth (GW259) is only known from a single sample (July 2015). The fifth (GW675f) and sixth (GW491m) specimen settled as a pair in September-October 2016 and gave birth to a litter of eight pups, of which at least six and possibly all eight were still alive by the end of 2017 (the “Ulfborg pack”). The seventh identified immigrant (GW781m) appeared in November 2017 and was registered from observations multiple times during rest of the year, traced throughout Jutland to reach the very northernmost part of Denmark. Evidence of an (as a minimum) eighth, unidentified individual, is based on three registrations from between November 2013 and August 2014. By the end of 2017, the three individuals that entered Denmark during 2016-17 were known to be still alive, while all individuals identified during 2012-15 had either died or disappeared. None of the wolves appearing in Denmark have subsequently been registered in Germany. All identified wolves located in Denmark were registered by genotype at least twice in Schleswig-Holstein and Denmark and at least annually.  Hence, all of the disappeared wolves are considered to have died in Denmark without being recovered.

A habitat suitability map was created from a habitat selection model (Resource Selection Function) with UTM-quadrat (10 x 10 km) as observation unit and the number of three month periods in which wolves had been recorded in each from 2012 to June 2017 as the response variable. The candidate model with highest support predicted wolf occurrence as a positive function of forest cover, heathland cover and population density of red deer (Cervus elaphus). The model, which had a high explanatory power (Somer’s D = 0.79), predicted 50% of all quarterly wolf occurrences in Jutland would be confined to 7% (22 out of 305) of UTM quadrats. The most suitable wolf habitats were mainly confined to areas in western and central Jutland, in northern Jutland, Thy and Djursland, whereas most of southern and eastern Jutland came out as being least suitable.

Apparent home ranges (100% Minimum Convex Polygons) created for the two resident male wolves (GW473m, GW373m) based on DNA-genotype samples were 353 km2 (n=10) and 33 km2 (n=6), respectively.  However, to judge from the distribution of wolf observations registered concurrently with the collection of genotyped samples (no wolves were observed in the areas before, between or after genotyped samples were registered), both males roamed throughout areas >500 km2. During the first 16 months of residence, the Ulfborg pair (which became a pack in 2017) were confined to within a total area of 78 km2 (n = 70 C1 and 41 C3a records). The size of the apparent home range appeared to be largest in the first six month after the pair had established, despite increased their energetic demands after reproduction.

The ability of the first (and to date only) female immigrant to mate, reproduce successfully and raise a large litter within one year of immigration into Denmark, demonstrates that wolves are perfectly able to establish packs and reproduce successfully in Denmark. It also suggests that at this stage at least, the establishment of the population has been hitherto female limited. With an average immigration rate from Germany of a minimum of 1.3 wolves year-1 (i.e. 8 in 6 years) during 2012-17, and a steadily growing population Germany, a minimum average immigration rate of 2 wolves year-1 (predominantly males) is expected from 2018 onwards. As the majority of the 6-8 pups from the Ulfborg pack (half of which are likely to be females) born in 2017 will reach independence in 2018 and seek mates, 1-2 new pairs are expected to establish annually in Denmark from 2018, unless the mortality rate (which so far appear to be lower than expected for a protected population) become prohibitively high.