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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.

A Correction to this paper has been published: https://doi.org/10.1007/s00265-021-03024-1

Bio-logging is becoming increasingly popular amongst wildlife researchers, providing a remote way of monitoring free-ranging animals in their natural habitats. However, capturing and tagging can be stressful and may alter animal behaviour. In this study, we investigated whether tagging altered activity and movement patterns of Eurasian beavers ( Castor fiber ) during the first week after release, predicting that beavers would be less active, travel shorter distances and stay closer to the lodge in the first nights after the tagging event. We captured 29 dominant free-ranging beavers (12 females, 17 males) in Telemark county, Norway, and tagged them with GPS units ( n  = 23; 12 males, 11 females) and tri-axial acceleration data loggers ( n  = 14; 9 males, 5 females). Accelerometer data was used to investigate activity levels (using mean overall dynamic body acceleration ODBA and principal activity periods), while GPS data was used to determine movement patterns (using distance moved and lodge displacement rate). Tagging effects were apparent only in activity levels of beavers, where we found lower mean ODBA values after release although the small effect size (Cohen’s d  = 0.17) indicates only a minimal difference in activity. Neither principal activity periods nor distances moved or lodge displacement rate changed within the first week after release, which indicates that beavers were active and post-release space use within the territory was not affected by the tagging event in this respect.

The confirmed presence of alien North American beavers in some regions of Eurasia may compete with and hinder the successful recolonisation of the native Eurasian species back to its former range. Distinguishing the two species in the field can be problematic, time consuming and expensive, thereby potentially limiting appropriate conservation actions. Here, a rapid and inexpensive genetic SNP assay is described that can separate the two species from either non-invasively collected samples or samples taken directly from restrained individuals. We applied these new genetic assays to free-living beavers of unknown origin sampled in Scotland.

The ability of gray squirrels (Sciurus carolinensis) to discriminate between different predator odors and the use of predator odors to deter gray squirrels from foraging on plants have not been previously investigated. To test the hypothesis that predator scent decreases foraging, I investigated the effect of such scent on consumption of butternuts (Juglans cinerea) in the field. Results showed that (i) red fox (Vulpes vulpes) scent was significantly more effective than either a control or human scent; (ii) raccoon (Procyon lotor) scent was significantly more effective than white-tailed deer (Odocoileus virginianus) scent (but only after 7–9 h); (iii) red fox scent was not significantly more effective than raccoon scent; and (iv) human scent was not significantly more effective than the control. The utility of predator odors in controlling damage by gray squirrels should be explored.

Background Delayed hypothermia, initiated after hospital arrival, several hours after cardiac arrest with 8-10 hours to reach the target temperature, is likely to have limited impact on overall survival. However, the effect of ultrafast hypothermia, i.e., delivered intra-arrest or immediately after return of spontaneous circulation (ROSC), on functional neurologic outcome after out -of -hospital cardiac arrest (OHCA) is unclear. In two prior trials, prehospital trans -nasal evaporative intra-arrest cooling was safe, feasible and reduced time to target temperature compared to delayed cooling. Both studies showed trends towards improved neurologic recovery in patients with shockable rhythms. The aim of the PRINCESS2-study is to assess whether cooling, initiated either intra-arrest or immediately after ROSC, followed by in -hospital hypothermia, significantly increases survival with complete neurologic recovery as compared to standard normothermia care, in OHCA patients with shockable rhythms. Methods/design In this investigator -initiated, randomized, controlled trial, the emergency medical services (EMS) will randomize patients at the scene of cardiac arrest to either trans -nasal cooling within 20 minutes from EMS arrival with subsequent hypothermia at 33 degrees C for 24 hours after hospital admission (intervention), or to standard of care with no prehospital or in -hospital cooling (control). Fever ( > 37,7 degrees C) will be avoided for the first 72 hours in both groups. All patients will receive post resuscitation care and withdrawal of life support procedures according to current guidelines. Primary outcome is survival with complete neurologic recovery at 90 days, defined as modified Rankin scale (mRS) 0-1. Key secondary outcomes include survival to hospital discharge, survival at 90 days and mRS 0-3 at 90 days. In total, 1022 patients are required to detect an absolute difference of 9% (from 45 to 54%) in survival with neurologic recovery (80% power and one-sided alpha= 0,025, beta = 0,2) and assuming 2,5% lost to follow-up. Recruitment starts in Q1 2024 and we expect maximum enrolment to be achieved during Q4 2024 at 20-25 European and US sites. Discussion This trial will assess the impact of ultrafast hypothermia applied on the scene of cardiac arrest, as compared to normothermia, on 90 -day survival with complete neurologic recover y in OHCA patients with initial shockable rhythm. Trial registration NCT06025123. (Am Heart J 2024;271:97-108.)

Beaver (Castor spp.) normally scent mark by depositing castoreum and/or anal gland secretion on scent mounds close to the water's edge. The aim of this study was to investigate the hypothesis that the Eurasian beaver (C. fiber) scent marks as a means of territory defense. Scent marking behavior was studied during an entire year (1 April 1995 - 31 March 1996) in 7 adjacent territories along 9.2 km of the Bø River in Telemark County, Norway. The number and location of fresh scent marks were recorded biweekly. The main results showed that:1) the number of scent marks in territories was significantly higher in spring, when dispersal of subadults normally occurs, than during the rest of the year; 2) the number of scent marks was clumped near territorial borders; and 3) the number of scent marks were significantly greater upstream than downstream of the lodge.

Subadult intruding beavers (Castor spp.) could be expected to pose a higher threat than adults to territory holders because, unlike adults who usually own a territory, subadults need to acquire a territory and a mate to reproduce successfully. We tested the responses of territorial beavers (Castor canadensis Kuhl, 1820) to simulated intrusions by adult and subadult males. Territorial intrusion was simulated through scent playback experiments that exposed residents to castoreum from adult and subadult strangers simultaneously. We obtained responses from 13 resident beavers. Neither sniffing response nor physical or total responses differed between castoreum from adults and subadults. This was true for both sexes combined and separate. There was also no significant correlation between the mass of the scent donor and the response intensity. We found no evidence that territorial beavers responded differentially to castoreum scent marks from intruders of different ages. Either beavers consider all strange intruders as posing a high threat and hence do not treat them differentially or castoreum does not contain sufficient information to allow beavers to discriminate between age classes. We suggest that rather than directly assessing intruders by means of intrinsic information contained in the scent mark, beavers assess their competitors through scent matching.

Eurasian beavers (Castor fiber) live in family groups that defend territories against other conspecifics. Part of this territorial defence involves constructing scent mounds near the stream bank within territories and marking them with castoreum, a urine-based fluid from the castor sacs, and (or) anal-gland secretion. The aim of this study was to test the hypothesis that Eurasian beavers show one or more forms of territorial behavior when an intruder, simulated in the form of experimental scent mounds (ESMs), has scent-marked inside the territory. We predicted that beavers would show a stronger response to ESMs with castoreum than to those without. Results showed that 85% of all beaver families (N = 20) made one or more behavioral responses to ESMs marked with castoreum from foreign adult males, whereas no ESMs presented without castoreum received a response. We therefore conclude that a main function of territorial marking by beavers is to advertise spatially related dominance status, thereby providing opportunities for intruders to assess the presence of the owner and reducing the cost and risks of agonistic conflict for both the owner and intruders. Additionally, it appears to be the scent emitted from an ESM and not the sight of it to which beavers respond.