Population dynamics of an island population of water voles Arvicola amphibius (Linnaeus, 1758) with one major predator, the eagle owl Bubo bubo (Linnaeus, 1758), in northern Norway

Abstract

Predator–prey relationships are of great significance to ecosystems, and their effects on the population dynamics of voles and lemmings (Microtinae) in Boreal and Arctic environments have long been of particular interest. A simple ecosystem with one major prey and one major predator could be an ideal setting for a study of their interactions. This is the situation on several small islands on the coast of northern Norway just below the Arctic Circle, with populations of water voles Arvicola amphibius preyed upon by the eagle owl Bubo bubo. The population dynamics of the water vole was studied by trapping and tagging in 2003–2018, eagle owl pellets were collected for analyses, eagle owl breeding attempts were recorded, and some weather variables collected from official recordings. After having been introduced well into the study period, the number of sheep Ovis aries was also recorded. Water voles were the main prey of the eagle owl, with 89% occurrence in pellets, with an overrepresentation of adults and males. Both predation, sheep grazing and extreme weather events influenced the vole population. Predator exclusion, as happened in three summers due to an intensive radio tracking study, especially increased the number of surviving young (in particular from the early cohorts) and the mass of adults. Extreme weather events, such as flooding in summer and deeply frozen ground in winter, most significantly reduced vole populations. Sheep grazing may exacerbate the effects of predation. A similar multitude of factors may affect populations of other rodent species as well.

Weight development in a northern island population of water voles Arvicola amphibius: approaching an optimal weight to survive the winter?

“…The water vole is the largest among all vole species, with a maximum male weight recorded in my study site of 267 g. The difference in size between juveniles/subadults and adults is striking, following rapid growth in spring. In my population, mortality due to predation was very high [20], consequently, breeding early (as first-summer juveniles) could have been advantageous pending the predation risk. This would have increased the population size much more than what was actually found [20].…”

“…In captivity, juveniles reached the asymptotic weight at 10 weeks [26]. Young may "leave the nest weighing as little as 30 g" [20] or 10 days old [27], perhaps permanently when 14 days old [30].…”

“…The water vole Arvicola amphibius is a large species among voles, weighing up to 350 g in Britain [19]. It lives in boreal and seasonal environments and is vulnerable to predation, weather conditions and food availability [20], but shows a remarkable ecological plasticity. About three times the size of a Microtus vole, the water vole's growth and development are of particular interest.…”

Numerical Response of Owls to the Dampening of Small Mammal Population Cycles in Latvia

“…A correlation was found between vole abundance in nature and their proportion in the diet, and the proportion of alternative prey was found to be nearly independent of its abundance in the field [ 166 ]. Several other studies highlight the high proportion of voles in the BUBBUB diet [ 167 , 168 , 169 ].…”

Numerical Response of Owls to Dampening of the Population Cycles of the Small Mammals in Latvia

“…The study found correlation between vole abundance in nature and their proportion in diet, and the proportion of alternative prey to be nearly independent of its abundance in the field [168]. There are several other studies highlighting the high proportion of voles in the BUBBUB diet [169][170][171].…”