In Denmark, American mink (Neovison vison) have been bred for their fur since the mid-1920s. Mink escaping from farms may supply the feral population. Often, it is of biological and management interest to separate the population of feral mink (i.e. mink caught in the wild) in two groups: 1) mink born on farms i.e., escapees, and 2) mink born in the wild. In this study, two methods were used for separating feral mink into the two groups: a) Comparison of body length of farmed mink and feral mink, and b) Presence of a biomarker (tetracycline: an oral antibiotic used on mink farms). A total of 367 wild caught mink (from the mainland of Denmark and the island of Bornholm), and 147 mink from farms, collected during the period 2014–2018, were used for the analysis of body length. For the testing of tetracycline (TC) as a biomarker, 78 mink from farms where there was knowledge about TC treatment (with or without) were examined for fluorescent markings in the canine teeth. Results from both univariate analyses and Gaussian mixture model analysis demonstrated clear divisions between the mean body length (mean ± S.E., range) of farmed males (52.1 cm ± 0.4, 48–68) and farmed females (mean 44.0 ± 0.2, 40–50), and between farmed mink and wild caught mink. Mixture analysis identified two groups within each sex of the wild caught mink, one assigned to farmed mink (born in captivity) and another group of smaller mink suspected of being born in the wild. On Bornholm, the mean (±SD, range) length of males born in the wild was 43.7cm (± 0.3, 36–57) and for females 37.5cm (± 0.3, 32–45). The mean length (±SD, range) of males born in the wild in the mainland of Denmark was 42.5cm (± 2.3, 36–46) and for females 36.1cm (± 1.0, 34–37). Among the feral mink from mainland Denmark, 28.4% of males and 21.6% of females were identified as escapees, while 0% of the males and 1% of the females were identified as escapees among the wild caught mink on Bornholm. Eight percent of mink from farms using tetracycline were false negatives, while no false positives were found among mink from farms not using TC. TC fluorescence was found in five of 217 mink caught in the wild equivalent to 22% escapees in mainland Denmark. No TC markings were found in mink caught in the wild on Bornholm. In conclusion, both methods a) the body length of mink, and b) fluorescent biomarkers in canine teeth are considered as useful tools to identifing mink that have escaped from farms.

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The stomach contents of 41 Arctic foxes (Vulpes lagopus) killed during winter and spring (December to June 1991-93) on Disko Island were examined. Fish, seabirds and marine invertebrates were found to be the most important winter food for Arctic foxes on Disko Island. Most fish remains in the stomachs were identified as capelin (Mallotus villosus), and cached fish appear to be important winter food for coastal foxes in the Disko Bay area. The stomachs of blue foxes contained more fish and marine invertebrates than those of white foxes, and stomachs of blue males contained more fish than those of blue females and white foxes of either sex. The age of 26 foxes was determined by X-rays and counting of annual lines in canine root cementum. Almost all the white foxes but less than a quarter of the blue foxes were in their first winter when harvested. The results of this study suggest that most of the white foxes were immigrants to Disko Bay while the blue foxes originated locally.

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Few studies have investigated the behaviour of zoo elephants and how their personality is expressed when exposed to different stimuli e.g. a higher number of visitors. Observing the nocturnal behaviour is especially important, because it reveals information about the welfare of the elephants when they are not normally observed. The nocturnal behaviour of three female African elephants (Loxodonta africana) in Aalborg Zoo, Denmark, was studied to create activity budgets and to evaluate if 1) a period with a 4.8 times increase in visitors affected the nocturnal behaviour; and 2) the three elephants exhibited differences in personality. Behavioural data were collected for six nights between 20:00-06:00, and all-occurrence sampling was used to record all types of behaviour. The average of the three elephants showed that the most common behaviours observed during the night was feeding (43±6%) followed by lying (28±5%) and inactive behaviour (16±5%). The elephants laid down an average of 2.4-3.1 hours per night starting at 20:00, and they never laid down before 22:00. No clear pattern of behavioural changes of the elephants was found when there was an increased number of visitors in the zoo. When comparing the intervals of time, the individuals spent on a certain behaviour, and thereby comparing the individuals, several significant differences were found between the medians and interquartile range (IQR). Significant differences were also found in the slopes of the medians, IQR, skewness, and kurtosis for the distribution of the time intervals of the behaviours between the period with lower number of visitors and the period with a higher number of visitors. In an overall perspective, the results indicated that the elephants displayed distinct personalities.