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Report2013

Re-evaluation of distance criteria for classification of lynx family groups in Scandinavia

Gervasi, Vincenzo; Odden, John; Linnell, John; Persson, Jens; Andren, Henrik; Bröseth, Henrik

Abstract

Monitoring of lynx populations in Scandinavia have largely been based around unreplicated minimum counts of family groups. Observations are accumulated from October 1st to February 28th in all parts of Scandinavia. Distance rules are used to separate or cluster observations of family groups when observations cannot be separated from each other on the basis of back- tracking in the snow. The aim of this report was to present a description of movement patterns of female lynx across the Scandinavian Peninsula, and to re-evaluate distance rules for classi- fication of lynx family groups. The maximum distance travelled by lynx females rapidly increased with time, up to about 10 days, after which it flattened to an asymptotic value, which approximates home range diameter. This suggests that different distance criteria should be applied for each of the first 10 days after the first observation of a family group, whereas a unique value should be applied for all subse- quent observations. We found large variation in movement patterns across Scandinavia, and we propose a classification of Scandinavia into 4 “eco-regions” based on predicted movement patterns. New distance rules for each of the four different “eco-regions” were calculated. Finally we provide an empirical validation of distance rules for the monitoring system. The distance rules are based on maximum travelled distances, and are therefore, by definition, conservative against the risk of overestimating the number of family units. The simulations showed that, while the estimator is unbiased when only one family unit occupies a given area, it becomes prone to underestimation when other neighbouring family units are present. The Swedish study sites had a higher probability of having neighbours compared to the Norwegian side, most like- ly as a result of a higher hunting pressure in Norway, and were therefore more likely to be af- fected by the risk of underestimating family units, when applying distance rules. We recom- mend that future data on the spatial arrangement of family units in Scandinavia should be used to validate these results. We also see a need for further evaluation of the distance rule method from areas where there are no movement data from GPS-collared female lynx in Scandinavia, and especially from areas in Sweden with high reported densities of family groups.

Published in

NINA rapport / Norsk institutt for naturforskning
2013, number: 965
ISBN: 978-82-426-2574-8
Publisher: NINA Report