Beaver (Castor fiber) activity patterns in a predator-free landscape. What is keeping them in the dark?

Short-term dynamics of beaver dam flow states

Beavers (Castor canadensis and C. fiber) build dams that modify catchment and pond water balances, and it has been suggested that they can be a nature-based solution for reducing flood hydrographs, enhancing low flow hydrographs and restoring hydrological functioning of degraded streams. How water moves through a beaver dam is determined by its flow state (e.g., overflow, underflow). However, current conceptual models only consider flow state as changing over the beaver site occupation-abandonment cycle. To assess whether flow state changes at shorter timescales and identify possible triggers (e.g., rainfall, animals), we integrated camera trap imagery, machine learning, water level measurements, and hydrometeorological data at beaver dams in a montane peatland in the Canadian Rocky Mountains. Contrary to current models, we found that flow states changed frequently, changing a maximum 12 times during the 139-day study period, but that changes had limited synchronicity amongst the dams in the same stream. More than two-thirds of the changes coincided with rainfall events. We observed no changes in flow state in response to beaver activity or wildlife crossings perhaps due to the camera positioning. Our findings augment the long-term oriented framework, which links changes to the occupancy cycle of a beaver pond and frequent and hydrological-driven changes. To develop realistic predictions of hydrological impacts of beaver dams, ecohydrological models should update their representation of the influence of beaver dams to include short-term dynamism of flow states and potential triggers. Our study advances the understanding of the important, yet understudied, role of beaver dams in stream restoration and climate change initiatives.

Temporal Activity Patterns of the Eurasian Beaver and Coexisting Species in a Mediterranean Ecosystem

Analyses of temporal partitioning and overlaps in activity rhythms are pivotal to shed light on interspecific coexistence between similar species or prey and predators. In this work, we assessed the overlap of activity rhythms between the Eurasian beaver Castor fiber and its potential competitors and predators through camera trapping in an area in Central Italy. Interspecific overlaps of temporal activity patterns were estimated for the beavers, potential predators (the red fox Vulpes vulpes and the grey wolf Canis lupus), and a potential competitor, the coypu Myocastor coypus. The beavers showed a mostly crepuscular behaviour. Although high temporal overlap was observed between the Eurasian beavers and the red foxes and grey wolves, the activity of the beavers did not overlap with that of the predators. Accordingly, the beavers were more active on the darkest nights, i.e., avoiding bright moonlight.

Movement Patterns of Resident and Translocated Beavers at Multiple Spatiotemporal Scales in Desert Rivers

Wildlife translocations alter animal movement behavior, so identifying common movement patterns post-translocation will help set expectations about animal behavior in subsequent efforts. American and Eurasian beavers (Castor canadensis; Castor fiber) are frequently translocated for reintroductions, to mitigate human-wildlife conflict, and as an ecosystem restoration tool. However, little is known about movement behavior of translocated beavers post-release, especially in desert rivers with patchy and dynamic resources. We identified space-use patterns of beaver movement behavior after translocation. We translocated and monitored nuisance American beavers in desert river restoration sites on the Price and San Rafael Rivers, Utah, USA, and compared their space use to resident beavers after tracking both across 2 years. Resident adult (RA) beavers were detected at a mean maximum distance of 0.86 ± 0.21 river kilometers (km; ±1 SE), while resident subadult (RS) (11.00 ± 4.24 km), translocated adult (TA) (19.69 ± 3.76 km), and translocated subadult (TS) (21.09 ± 5.54 km) beavers were detected at substantially greater maximum distances. Based on coarse-scale movement models, translocated and RS beavers moved substantially farther from release sites and faster than RA beavers up to 6 months post-release. In contrast, fine-scale movement models using 5-min location intervals showed similar median distance traveled between RA and translocated beavers. Our findings suggest day-to-day activities, such as foraging and resting, were largely unaltered by translocation, but translocated beavers exhibited coarse-scale movement behavior most similar to dispersal by RSs. Coarse-scale movement rates decreased with time since release, suggesting that translocated beavers adjusted to the novel environment over time and eventually settled into a home range similar to RA beavers. Understanding translocated beaver movement behavior in response to a novel desert system can help future beaver-assisted restoration efforts to identify appropriate release sites and strategies.

Size is not everything: differing activity and foraging patterns between the sexes in a monomorphic mammal

Abstract

Animals balance foraging with other activities, and activity patterns may differ between sexes due to differing physical requirements and reproductive investments. Sex-specific behavioural differences are common in sexually dimorphic mammals, but have received limited research attention in monomorphic mammals where the sexes are similar in body size. Eurasian beavers (Castor fiber) are obligate monogamous and monomorphic mammals and a good model species to study sex-specific differences. As females increase energy expenditure during reproduction, we hypothesized differing seasonal activity budgets, circadian activity rhythms and foraging patterns between male and reproducing female beavers. To test this hypothesis, we equipped adult beavers with VHF transmitters (N=41; 16 female, 25 male) and observed them throughout their active period at night from spring to late summer. Occurrence of their main activities (foraging, travelling and being in lodge) and use of food items (trees/shrubs, aquatic vegetation and herbs/grasses) were modelled to investigate sex-specific seasonal activity budgets and circadian activity rhythms. The sexes did not differ in time spent foraging across the season or night, but during spring, females resided more in the lodge and travelled less. Males and females both foraged on aquatic vegetation during spring, but females used this food source also during late summer, whereas males mostly foraged on trees/shrubs throughout the year. We conclude that seasonal activity budgets and foraging differ subtly between the sexes, which may relate to different energy budgets associated with reproduction and nutritional requirements. Such subtle seasonal behavioural adaptions may be vital for survival and reproduction of monomorphic species.

Significance statement

Activity budgets and foraging patterns of animals are key to their survival and may differ between males and females with different body sizes and physical requirements. In monomorphic species, where males and females have similar body sizes, fewer differences are expected, but may still be pronounced during certain times of the year. We modelled sex-specific seasonal activity budgets and circadian activity rhythms and use of food items in a monomorphic mammal, the Eurasian beaver. By treating season and time of day as a continuous variable rather than modelling differences within distinct predefined periods, we identified subtle sex-specific seasonal trends in activity budgets and use of food items.

Eurasian Beaver (Castor fiber) Winter Foraging Preferences in Northern Poland-The Role of Woody Vegetation Composition and Anthropopression Level

Simple Summary

The food preferences of beavers depend on many factors, such as forage taxonomy, stem diameter, and the distance from a riverbank. In this study, we investigated beavers’ diets and food preferences in an urban area of northern Poland subject to varying levels of human disturbance. In the course of the study, we confirmed a similar preference for the browsing of woody plants, as described in other studies. The most popular and preferred woody plants in beaver’s diet were willows and maples, and most woody plants were characterized by a stem diameter less than 10 cm. We also found that human disturbance played an important role in shaping the beavers’ diets. We discussed this phenomenon from the basis of optimal foraging theory.

Abstract

We studied beavers’ dietary preferences and the role of several factors (such as plant species, size and anthropopression level) that affect the beavers’ foraging in northern Poland. Woody plants along the river were measured and classified according to species in six 100 m-long transects that were characterized by a diversified human disturbance level. Ivlev’s electivity index was used to present the beavers’ preferences for various plant species and sizes, and the generalized linear model was used to assess the significance of studied factors in beavers’ browsing choices. Most popular in the beavers’ diets were willows (Salix), maples (Acer) and alder (Alnus), but only willows and maples were preferred. We noted a decrease in the beavers’ foraging preference in parallel to an increase in the shoot diameter; plants with a diameter below 10 cm were preferred. All factors included in the generalized linear model (GLM) were significant in shaping the beavers’ foraging choices. A negative correlation between the shoot diameter and the human disturbance level was found, but the species composition of the browsed woody plants was the same in each transect. Beavers’ foraging preferences, as observed in our study, were similar to those described in the literature and confirmed the role of woody species and their diameters in shaping the beavers’ diet. We also suggested the potential role of anthropopression in the shaping of the beavers’ foraging behaviors.

Patterns of activity rhythms of invasive coypus Myocastor coypus inferred through camera-trapping

Studies on activity rhythms are pivotal for the management of invasive alien species, as they provide basic insights into species basic ecology and may increase the success of control programs. The coypu Myocastor coypus, introduced from South America for fur farms, has become one of the most invasive rodents in Europe. Introduced coypus may affect crop productions, as well as natural vegetation and the breeding success of wading birds. In this study, we examined activity data collected through intensive camera-trapping in three Italian areas, including two natural areas in Northern and Central Italy, and a suburban area in Central Italy. Coypus were mostly diurnal in areas characterised by low predator pressure and, at night, they are mostly active in bright moonlight. Conversely, where predators, human pressure or numerical control programmes are present, coypus remarkably shift their behaviour towards crepuscular and night hours. In these last areas, nocturnal activity increased as moonlight decreased, possibly to reduce predation risk or encounters with humans. Where winter temperature are low, diurnal habits may have developed as a physiological adaptation and a strategy to preserve energy, potentially achieving a cost/effective thermal balance.

Beaver (Castor fiber) activity and spatial movement in response to light and weather conditions

Animal behaviour can affect individual fitness and is influenced by exogenous and endogenous factors. Here, we investigated how light (daylight length and moonlight), weather (precipitation and temperature), age, sex and social status affected activity and movement of a semiaquatic mammal, the Eurasian beaver (Castor fiber), using GPS relocation data from 47 individuals in south-eastern Norway. Independent of daylight length, beavers had a mean daily activity time of 9:42 h and reduced their activity periods when they were older, most likely due to senescence. In line with this, older individuals also spent less time in water and moved shorter distances. Furthermore, beavers reduced their activity periods in drier weather conditions and spent less time on land during brighter nights and drier conditions, indicating a predation risk avoidance strategy. Individuals spent less time in the water during the colder parts of the year and moved shorter distances with decreasing temperature, suggesting thermal constraints. Our study adds to the increasing amount of evidence that animal behaviour is modulated by various endogenous and exogenous factors, and that weather conditions can affect their behaviour. It remains to be tested, however, how climate variability together with hunting and predation pressure affect space use and demography in species such as the Eurasian beaver.

Framing pictures: A conceptual framework to identify and correct for biases in detection probability of camera traps enabling multi-species comparison

Obtaining reliable species observations is of great importance in animal ecology and wildlife conservation. An increasing number of studies use camera traps (CTs) to study wildlife communities, and an increasing effort is made to make better use and reuse of the large amounts of data that are produced. It is in these circumstances that it becomes paramount to correct for the species- and study-specific variation in imperfect detection within CTs. We reviewed the literature and used our own experience to compile a list of factors that affect CT detection of animals. We did this within a conceptual framework of six distinct scales separating out the influences of (a) animal characteristics, (b) CT specifications, (c) CT set-up protocols, and (d) environmental variables. We identified 40 factors that can potentially influence the detection of animals by CTs at these six scales. Many of these factors were related to only a few overarching parameters. Most of the animal characteristics scale with body mass and diet type, and most environmental characteristics differ with season or latitude such that remote sensing products like NDVI could be used as a proxy index to capture this variation. Factors that influence detection at the microsite and camera scales are probably the most important in determining CT detection of animals. The type of study and specific research question will determine which factors should be corrected. Corrections can be done by directly adjusting the CT metric of interest or by using covariates in a statistical framework. Our conceptual framework can be used to design better CT studies and help when analyzing CT data. Furthermore, it provides an overview of which factors should be reported in CT studies to make them repeatable, comparable, and their data reusable. This should greatly improve the possibilities for global scale analyses of (reused) CT data.

The influence of periodic increases of human activity on crepuscular and nocturnal mammals: Testing the weekend effect

Human recreation can negatively affect wildlife, particularly on weekends when human activity is highest (i.e., the weekend effect). Much of what we understand about the weekend effect is based on research conducted on diurnal species, which have greater temporal overlap with humans. Because nocturnal species generally avoid times when humans are active, they are likely less affected by anthropogenic activity on weekends. Our objective was to test the weekend effect in relation to the degree of nocturnality of mammals in a recreational area. We predicted that as nocturnality increased, the effect of human activity would decrease. To address our objective, we placed 50 remote cameras along the Diamond Fork River in Utah from January to June 2015. We found that three out of the four focal species supported our predictions. Mule deer (crepuscular) reduced activity throughout our entire study area during weekends and avoided campgrounds. Beavers and mountain lions (both nocturnal) did not negatively respond to increased human activity. Raccoons (nocturnal) reduced activity during weekends, but only within campground areas. Our findings indicate that as the temporal overlap increases between wildlife and humans, so does the influence that humans have on wildlife.

Lack of sex-specific movement patterns in an alien species at its invasion front - consequences for invasion speed

Efficient targeting of actions to reduce the spread of invasive alien species relies on understanding the spatial, temporal, and individual variation of movement, in particular related to dispersal. Such patterns may differ between individuals at the invasion front compared to individuals in established and dense populations due to differences in environmental and ecological conditions such as abundance of conspecifics or sex-specific dispersal affecting the encounter rate of potential mates. We assessed seasonal and diurnal variation in movement pattern (step length and turning angle) of adult male and female raccoon dog at their invasion front in northern Sweden using data from Global Positioning System (GPS)-marked adult individuals and assessed whether male and female raccoon dog differed in their movement behavior. There were few consistent sex differences in movement. The rate of dispersal was rather similar over the months, suggesting that both male and female raccoon dog disperse during most of the year, but with higher speed during spring and summer. There were diurnal movement patterns in both sexes with more directional and faster movement during the dark hours. However, the short summer nights may limit such movement patterns, and long-distance displacement was best explained by fine-scale movement patterns from 18:00 to 05:00, rather than by movement patterns only from twilight and night. Simulation of dispersing raccoon dogs suggested a higher frequency of male-female encounters that were further away from the source population for the empirical data compared to a scenario with sex differences in movement pattern. The lack of sex differences in movement pattern at the invasion front results in an increased likelihood for reproductive events far from the source population. Animals outside the source population should be considered potential reproducing individuals, and a high effort to capture such individuals is needed throughout the year to prevent further spread.

Sitka black-tailed deer (Odocoileus hemionus sitkensis) adjust habitat selection and activity rhythm to the absence of predators

Although individuals must generally trade off acquisition of high-quality resources against predation risk avoidance, removal of top predators by humans has resulted in many large herbivores experiencing novel conditions where their natural predators are absent. Antipredator behaviors should be attenuated or lost in such a context of relaxed predation pressure. To test this prediction, we analyzed daily and seasonal habitat selection and activity rhythm (both commonly linked to predation risk) of GPS-collared Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898) on predator-free islands (British Columbia, Canada). In marked contrast to the behavioral patterns commonly observed in populations subject to predation risk, we documented a very low day–night contrast in habitat selection. Moreover, we observed higher activity during daytime than nighttime, as expected for nonhunted populations. We also showed that resource selection was primarily driven by seasonal variations in resource availability. These results are consistent with the expected attenuation of antipredator behaviors in predation-free environments. However, we also observed marked crepuscular activity peaks, which are commonly interpreted as an antipredator response in ungulates. Our study indicates that large herbivores are able to adjust certain antipredator behaviors under relaxed selection, notably habitat selection and activity rhythm, while others persist despite the long-term absence of predators.