Roads constrain movement across behavioural processes in a partially migratory ungulate

Background Human disturbance alters animal movement globally and infrastructure, such as roads, can act as physical barriers that impact behaviour across multiple spatial scales. In ungulates, roads can particularly hamper key ecological processes such as dispersal and migration, which ensure functional connectivity among populations, and may be particularly important for population performance in highly human-dominated landscapes. The impact of roads on some aspects of ungulate behaviour has already been studied. However, potential differences in response to roads during migration, dispersal and home range movements have never been evaluated. Addressing these issues is particularly important to assess the resistance of European landscapes to the range of wildlife movement processes, and to evaluate how animals adjust to anthropogenic constraints. Methods We analysed 95 GPS trajectories from 6 populations of European roe deer (Capreolus capreolus) across the Alps and central Europe. We investigated how roe deer movements were affected by landscape characteristics, including roads, and we evaluated potential differences in road avoidance among resident, migratory and dispersing animals (hereafter, movement modes). First, using Net Squared Displacement and a spatio-temporal clustering algorithm, we classified individuals as residents, migrants or dispersers. We then identified the start and end dates of the migration and dispersal trajectories, and retained only the GPS locations that fell between those dates (i.e., during transience). Finally, we used the resulting trajectories to perform an integrated step selection analysis. Results We found that roe deer moved through more forested areas during the day and visited less forested areas at night. They also minimised elevation gains and losses along their movement trajectories. Road crossings were strongly avoided at all times of day, but when they occurred, they were more likely to occur during longer steps and in more forested areas. Road avoidance did not vary among movement modes and, during dispersal and migration, it remained high and consistent with that expressed during home range movements. Conclusions Roads can represent a major constraint to movement across modes and populations, potentially limiting functional connectivity at multiple ecological scales. In particular, they can affect migrating individuals that track seasonal resources, and dispersing animals searching for novel ranges.

Are less vocal rainforest mammals susceptible to impacts from traffic noise?

Context Traffic noise is believed to cause road avoidance and other barrier effects in a variety of wildlife species, and to force changes to call pitch or loudness in others; however, this has never been tested in the absence of other road impacts. Noise impacts on species that do not frequently vocalise are also poorly understood. We investigated traffic-noise impacts on the following three rainforest mammals that do not often vocalise: Hypsiprymnodon moschatus, Uromys caudimaculatus and Perameles nasuta. These species have previously been observed to exhibit varying levels of road avoidance. Aims To determine whether traffic noise affects movement and behaviour of medium-sized, ground-dwelling rainforest mammals in the absence of other road-associated variables and potential impacts. We hypothesised that noise impacts would be greatest for species previously shown to avoid roads. Noise impacts on these less vocal species compared with more vocal species is also discussed. Methods In north-eastern Queensland, Australia, mammals captured at least 500 m from any road were tracked after fitting with spool-and-line equipment. On noisy nights, traffic noise at levels similar to a busy highway was played continuously throughout the night from a line of 12 speakers mounted on trees. Speakers were silent on quiet nights. Key results Traffic noise caused no increase in avoidance of the speaker line and was not a barrier to movements across the line. Overall, movement paths on noisy nights appeared similar in pattern (tortuosity) to those of quiet nights. At a finer scale, movements of H. moschatus and P. nasuta became more tortuous later in the track, suggesting a return to normal foraging behaviour and possible habituation to the noise. Conclusions These three species with varying levels of previously recorded road avoidance, did not respond negatively to traffic noise. There was, however, a suggestion of habituation by H. moschatus and P. nasuta in response to the noise. Implications The demonstrated lack of response to traffic noise in these less vocal species means that traffic noise is unlikely to cause road avoidance or barrier effects. Instead, lack of response and possible habituation to traffic noise may increase vulnerability to road mortality.