Road bund landscapes as habitat: a main asset for rodents in an intensive farming landscape

Since the 1970’s the intensive farming has led to shape new landscapes of huge single-crops fields, often to the detriment of natural refuges for small mammals and birds, like hedgerows or groves. This type of landscape is frequent in Alsace (France) where hectares are only covered by corn and wheat without interruption leading us to speak about biological desert or unstable ecosystem. Indeed, about the few species living there like rodents, wheat fields are mown during the breeding season in July and corn fields cannot be considered as habitat for these species. They therefore have to survive from July to April without refuges, but few survive more than a few weeks.

When a road is built, potential substitution environments (named road bound landscape elements or RBLE) appear like (1) road verges, (2) storm-water basins, (3) excavation slopes or even (4) middle of roundabouts. Indeed, road verges are for example well known to be habitats for some butterflies, orchids or rodents and storm-water basins are frequently occupied by amphibians or birds. However, the habitat potentiality of all RBLE is not known and even if they could be beneficial for the environment, such hypothesis is not considered during current road environmental studies. Thus, to study the ability of RBLE to be suitable habitats, we have compared these 4 RBLE to two different usual crops fields of corn and wheat. Four replicates of these 6 different habitats were selected in an intensive farming landscape.

To characterize differences in habitat quality, indexes of rodents populations abundance (capture-mark-recapture) and qualities (body condition and survival based on Huggin’s Robust Design model) have been investigated. The study was conducted from May 2015 to August 2015 with 4 captures sessions of 4 consecutive days.

We captured 3166 micromammals with an average of 66 individuals per day. These individuals were distributed in four different species: wood mouse (Apodemus sylvaticus), bank vole (Myodes glareolus), commun vole (Microtus arvalis) and Greater white-toothed shrew (Crocidura russula). Following results concern Microtus arvalis only. We found a greater abundance of individuals in every RBLE than in controls (7.5 times more in average), with almost no individuals in corn crops (< 2 per studied crop). This effect is even stronger in July when wheat crops are mown (0,2 individuals/m² in RLBE vs 0,006 individuals/m² in controls). There is also no significant difference in terms of survival and body condition index between sites with sufficient captured individuals (RLBE and wheat corn only).

These results lead us to consider all road bund landscapes elements (not only road verges) as sustainable habitats which can favor both rodents (and probably shrews too) and predators communities. However, the respective advantages (rodent vs predators) may be difficult to consider in the light of the Predation Release Hypothesis: i.e. a small number of predators will profit of these RBL habitats.

We recommend taking account damages these rodents can cause to nearest crops (financial compensations to farmers), road hedgerows (plants protections, fences) and structures like basins during roads environmental impact studies and road conception, particularly in years of great rodent abundance. Finally, if the rodents’ abundances in RBLE have to be decreased, the employed methods need to be considered in the light of other RBLE taxa such as butterflies and orchids.

roads bund landscapes ; road verges ; rodents ; landscape ecology ; habitat ; Microtus