Forsøksdyr: Camera traps for density estimation: Calibration of camera traps using density estimates of voles from capture recapture methods.


Godkjenningsdato 31.03.2020

Godkjenningsperiode 01.06.2020-31.05.2022

This study will investigate the ability of camera traps to estimate density of a broad set of small rodent species, including gray-sided vole (Myodes rufocanus), tundra vole (Microtus oeconomus), northern red-backed vole(Myodes rutilus), field vole (Microtus agrestis) and bank vole (Myodes glareolus) For such a calibration an accurate density estimate is crucial and live trapping data analyzed with capture-recapture methods is today seen as most accurate. This method requires animal to be trapped in live traps filled with food and water and checked at frequent intervals. When new animals are trapped they will be pit-tagged so they can be recognized in later encounters (recaptures).

If this study succeed, non-invasive camera traps can replace invasive live traps and snap traps (that kill the animals) that today are commonly used in small mammal research. Hence, this study can both replace, reduce and refine the use of live animals in future small rodent population monitoring. Moreover, researchers will be able to monitor small mammals with greater temporal and spatial resolution with lower costs then they have today and even with seasons when standard trapping is impossible. We have done some pilot studies with the camera trap and we really think this method may change field studies of small rodents from being invasive to completely non-invasive. However, to convince the community of mammalogist that do research on small rodent population ecology in the field we need a robust calibration study with fairly big samples and trials on a set of different species. And that is what we intend to by this proposal. Most small rodent species in Scandinavia have 3-5-year population cycles and we need to cover all years/phases of these cycles for all the species in two seasons, spring and fall, since movements patterns and trappability are both known to be phase-, season - and species-dependent.

For statistical purposes we need at least 10 spatial replicates of local populations of all the species for each phase/year of the 4-5 year population cycles. We were granted permssion to perform these trials for the year 2018-2019. Here we apply for a continuation of the trials for the years 2020-2021 in order to cover more years/cycle phases. With 10 spatial population replicates X 2-years X 2 seasons per species and assuming a capture per trap per trapping session of 10 animals (based on previous experience), we expect that we will catch a maximum 400 individuals per species. These species are sympatric while the trapping method is not species-specific. Therefore we will trap more of the two most common species, gray-sided vole and tundra vole to reach the minimum number needed of the three other species. Therefore, we want to trap a maximum of 1500 individual grey-sided vole and 800 individual tundra vole over the two years. In total this yields maximum 3500 individuals. Our experience from the years 2019-2020 indicates that we have adequate replication in terms of local populations and number of tagged individuals for our purpose of statistically validating the new camera trapping method.