One of the most studied problems in population ecology has been to understand the relative roles of top–down and bottom–up forces in regulating animal populations. This has also been a key issue in studies of vole population dyna mics. Vole populations exhibit a wide variation of dynamics, from seasonal fluctuations to multiannual variations or cyclicity. One of the hypotheses to explain cyclic population dynamics is predation by the specialist predators. A common counterargument against the predation hypothesis has been the lack of conclusive observations of the time delay in the predators’ numerical response. We studied the interaction between voles and their specialist small mustelid predators, the stoat Mustela erminea and the least weasel Mustela n. nivalis, by modelling their interaction to data sets that cover large areas of Finland. Vole abundance was monitored with biannual trappings and their predators with snow‐tracking. Results show a high dependence of the predators on the voles, and this connection is generally tighter in weasels than in stoats. Weasel abundance is affected most strongly by the vole abundance in previous spring, 8.5– 10 months earlier, while in stoats the effect of autumn abundance of voles, 2.5–6 months earlier, was the strongest. These results, together with the observation that the weasels’ effects on voles are stronger after a time lag of 6–9.5 than 2–4.5 months, indicate the existence of a time lag in weasels’ numerical response. A time lag in the predators’ numerical response is a necessary condition for the predators to drive population cycles in its prey, and therefore our results support the specialist predation hypothesis.

Large-scale spatial and temporal patterns in population dynamics of the stoat, Mustela erminea , and the least weasel, M. nivalis, in Finland. Á Oikos 115: 286 Á298.The stoat and the least weasel are specialist predators of small rodents, and therefore their numbers are likely to depend on the availability of voles. These small predators are ecologically alike, but they differ somewhat in their diet. The stoat is larger in size than the least weasel and therefore capable of using a wider variety of prey species, while the least weasel is more restricted to small mammals. Voles in northern Fennoscandia exhibit cyclic dynamics of 3 Á5 years with large-scale spatial synchrony and geographical trends in cycle length and amplitude. We predicted that the cyclic dynamics of voles are reflected in the dynamics of their predators with slight differences between the stoat and the least weasel. In this study we use snow-tracking data to characterize the dynamics of small mustelids. The data were collected from different parts of Finland using permanent triangle-shaped census routes of 12 km in 1989 to 2003. Population fluctuations of small mustelids were generally multiannually periodic and in synchrony over large areas, but we did not find any clear geographical gradient in the attribute of small mustelid dynamics comparable to those observed in vole population fluctuations. Instead, we found a similar decreasing temporal trend in the abundances of both species as has been recently reported for voles. P. Hellstedt (paavo.hellstedt@helsinki.fi) and J. Sundell,

BackgroundA multi-faceted approach was used to investigate the wintertime ecophysiology and behavioral patterns of the raccoon dog, Nyctereutes procyonoides, a suitable model for winter sleep studies. By utilizing GPS tracking, activity sensors, body temperature (Tb) recordings, change-point analysis (CPA), home range, habitat and dietary analyses, as well as fatty acid signatures (FAS), the impact of the species on wintertime food webs was assessed. The timing of passive bouts was determined with multiple methods and compared to Tb data analyzed by CPA.ResultsRaccoon dogs displayed wintertime mobility, and the home range sizes determined by GPS were similar or larger than previous estimates by radio tracking. The preferred habitats were gardens, shores, deciduous forests, and sparsely forested areas. Fields had close to neutral preference; roads and railroads were utilized as travel routes. Raccoon dogs participated actively in the food web and gained benefit from human activity. Mammals, plants, birds, and discarded fish comprised the most important dietary classes, and the consumption of fish could be detected in FAS. Ambient temperature was an important external factor influencing Tb and activity. The timing of passive periods approximated by behavioral data and by CPA shared 91% similarity.ConclusionsPassive periods can be determined with CPA from Tb recordings without the previously used time-consuming and expensive methods. It would be possible to recruit more animals by using the simple methods of data loggers and ear tags. Hunting could be used as a tool to return the ear-tagged individuals allowing the economical extension of follow-up studies. The Tb and CPA methods could be applied to other northern carnivores.

We monitored the home ranges, habitat use and activity of stoats Mustela erminea in north-west Finnish Lapland with radio-tracking in years 1998 and 1999, and found a dominance hierarchy in habitat use between and within sexes. Altogether, eight female and seven male stoats were caught and radio-tracked. Males and females differed from each other both in the size of their home ranges and in habitats. Mature females live in areas where the abundance of the preferred Microtus prey is the highest. Dominant males lived in less productive habitats than females, but in more productive areas than non-dominant mature males. Furthermore, both male and female activity levels were higher during the snowless nonbreeding season than the breeding season, but we found no activity differences between sexes through the diurnal cycle. We compare the results from Finnish Lapland with those from other regions, and discuss the flexibility of stoat behaviour in subarctic conditions.

The behaviour and survival of captive-born least weasels Mustela nivalis nivalis released in nature were reported in this study. Altogether 27 captive-born and six wild-caught weasels were equipped with radio transmitters and their survival was studied as a function of age and season. The daily mortality rate was generally higher in captive-born than in wild-caught weasels. The survival of captive-born weasels was highest if they were released during the summer and hence when they were young. Differences in the behavioural patterns of captive-born and wild-caught weasels were apparent. Captive-born weasels were often more visible in the field and were less timid than wildcaught weasels. Results suggest that to be successful, restocking of weasels should be done with young animals, which are preferably released during the season with abundant food resources.