The breeding suppression hypothesis predicts that females of certain small mammal species will reduce reproduction as a response to the odour of a specialised mammalian predator. This was tested in a field experiment with grey-sided voles (Clethrionomys rufocanus) during three summer seasons (1997-1999) in the subalpine tundra of northern Norway, which is a natural habitat of this species. In a first phase free-ranging voles in six unfenced 1-ha plots were monitored by live-trapping from June to August each year. In a second phase from August to September, three of the plots were sprayed with weasel (Mustela nivalis) odour to simulate increased apparent predation risk, while the remaining three plots served as untreated controls. On all plots voles were individually marked with ear tattoos and were regularly live-trapped during the whole breeding season to follow their performance. On the treatment plots the recruitment rate of juveniles did not increase in late summer as it did on the control plots. The proportion of reproductively non-active adult females was significantly higher on the treatment plots for both old and young females. Our results thus verify the breeding suppression hypothesis for the first time under natural conditions. However, the response in overwintered females is in conflict with the original hypothesis because the assumed fitness benefits from breeding delayed until the next season are inaccessible to them. As an alternative explanation we propose a short-term response of reduced activity and interrupted breeding until the predator has exploited and left the feeding patch. Such a "duck and cover" strategy would increase the fitness of females of all age classes when prey habitats are patchy.
In a ®eld study on the behavioural response of grey-sided voles Clethrionomys rufocanus to predator odour ear tattoos were used for individual marking of the voles in the ®eld. The study was conducted over three summer seasons in the tundra of northern Norway. In this paper we report our experience with eartattooing in order to compare it with other methods used for marking small mammals. Methods should be compared for their different in¯uences on physiology and behaviour and to ®nd alternatives to the widely used toe-clipping. Looking for alternatives becomes mandatory because in many countries this method needs a special permit or is totally prohibited by law. Marking a vole with ear-tattoos took us 2 min on average. The rate for the ®rst recapture after marking voles was 87%. This is much higher than reported recapture rates for toe-clipped voles. From all recaptured individuals we were able to identify > 89.9% of the codes. The time lag between marking and ®rst recapture was higher than the lag between second and third recapture, which indicates a trauma caused by the marking procedure. However, there was no evidence of any weight loss as reported for other marking methods, and most of the tattooed animals did not show any behaviour indicating irritation after being marked. It is concluded that ear-tattooing, as an alternative to other methods of marking small mammals is useful even in the ®eld. However, to assess different advantages and disadvantages in other circumstances, the chosen method should be examined critically before use.
Trapping small mammals is frequently used to study the dynamics, demography, behavior and presence of pathogens. When only particular small mammal species are in the focus of interest, all other species are unnecessary bycatch. We analyzed data from extensive live trapping campaigns conducted over the last decade in Germany, following a consistent standard trapping protocol that resulted in about 18,500 captures of small mammals. Animals were trapped with Ugglan multiple capture traps in grassland, forest and margin habitat. Trap success and the proportion of bycatch were about 30% when target species were common voles (Microtus arvalis) in grassland and common voles and bank voles (Clethrionomys glareolus) in margins and forests. This was more pronounced in spring and along margins. Species mentioned in the early warning list according to the Red List Germany were higher in numbers and proportion in spring and in grassland. The results will help to avoid periods with enhanced presence of bycatch, including endangered species (if the purpose of the study allows) or to pay particular attention in certain seasons and habitats when the occurrence of bycatch is most likely.
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