Camilla Wikenros

Effects of hunting group size, snow depth and age on the success of wolves hunting moose

To study factors important to the success of wolves, Canis lupus, hunting moose, Alces alces, we analysed data from more than 4000 km of snow tracking of wolves during 1998e2003 in Scandinavia. We used two methods to estimate hunting success for 17 wolf territories from 185 observations of wolf attacks on moose. On average, hunting success was estimated at 45 and 64% for the two methods, respectively. We used a smaller data set (N ¼ 142) to examine the effect of age of breeding wolves, hunting group size, snow depth and moose density on hunting success. Multiple logistic regression showed that age of breeding males was the only variable significantly related to hunting success, with maximum hunting success at 4.5e5.5þ years of age. We also studied prey selection of radiocollared adult wolves over successive winters in two wolf packs that lost one of the breeding wolves. Whereas the surviving adult female switched to prey on roe deer, Capreolus capreolus, the surviving adult male continued mainly to select moose. Our results suggest that the positive effect of male age on hunting success reflects both increased experience of attacking prey and possibly the greater size of adult male wolves (25e30%) compared to adult female wolves.

Cross-continental differences in patterns of predation: will naive moose in Scandinavia ever learn?

Predation has been recognized as a major selective force in the evolution of behavioural characteristics of mammals. As a consequence of local predator extinction, prey may lose knowledge about natural predators but usually express behavioural adjustments after return of predators. Human harvest may replace natural predation but prey selection may differ from that of natural predators leading to a change in the behavioural response of prey. We show that hunting success (HS) of re-colonizing wolves (Canis lupus) on moose (Alces alces) in Scandinavia was higher than reported in North America, where moose have been continuously exposed to wolves and grizzly bears. We found no evidence that moose expressed behavioural adjustments that lowered the HS of wolves in territories that had been occupied by wolves for up to 21 years. Moose behaviour towards wolves and humans typically differs in Scandinavia compared to North America. We explain the differences found to be caused by variation in predation pressure by large carnivores and the rate, and mode, of human harvest during the twentieth century.

Wolf predation on moose and roe deer: chase distances and outcome of encounters

We examined chase distances of gray wolves Canis lupus Linnaeus, 1758 hunting moose Alces alces and roe deer Capreolus capreolus, and recorded details of encounters between wolves and prey on the Scandinavian Peninsula, 1997–2003. In total, 252 wolf attacks on moose and 64 attacks on roe deer were registered during 4200 km of snow tracking in 28 wolf territories. Average chase distances were 76 m for moose and 237 m for roe deer, a difference likely due to variation in body size and vigilance between prey species. A model including prey species, outcome of the attack, and snow depth explained 15–19% of the variation found in chase distances, with shorter chase distances associated with greater snow depth and with successful attacks on moose but not on roe deer. Wolf hunting success did not differ between prey species (moose 43%, roe deer 47%) but in 11% of the wolf attacks on moose at least one moose was injured but not killed, whereas no injured roe deer survived. Compared with most North American wolf studies chase distances were shorter, hunting success was greater, and fewer moose made a stand when attacked by wolves in our study. Differences in wolf encounters with moose and roe deer likely result from different anti-predator behaviour and predator-prey history between prey species.

Biomass Flow and Scavengers Use of Carcasses after Re- Colonization of an Apex Predator

Background Reestablishment of apex predators influences the availability and distribution of biomass for scavengers and can therefore be an important agent for structuring species communities. We studied how the re-colonization of the Scandinavian Peninsula by wolves (Canis lupus) affected the amount and temporal variation in use of moose (Alces alces) carcasses. Methodology/Principal Findings We compared the availability of biomass from remains at wolf kills with those killed by hunters, vehicle collisions and natural death. Movement-triggered cameras monitored patterns of use on wolf kills and remains from hunter harvest by scavengers (n = 15 276) in relation to time of year, available carcass biomass, time since the death of the moose and presence of wolves. Remains from hunter harvest were the largest food source for scavengers both within wolf territories (57%) and in areas without wolves (81%). The total annual biomass available were similar in areas with (25 648 kg) and without (24 289 kg) wolves. Presence of wolves lowered the peak biomass available from hunter harvest in October (20%) and increased biomass available during December to August (38–324% per month). The probability of scavengers being present decreased faster with time at remains from hunter harvest compared to wolf kills and both the probability of being present and the number of visits by scavengers to wolf kills increased as the amount of biomass available on the carcass increased. Conclusions/Significance Wolves reduced the seasonal variation of biomass from moose carcasses and most important increased it during spring. Scavengers also visited wolf kills most frequently during spring when most scavenging species have young, which may lead to an increase in survival and/or reproductive success of scavengers within wolf territories. This applies both for abundant scavenging species that were the most frequent visitors at wolf kills and threatened scavengers with lower visit frequency.

Behavioural responses of ungulates to indirect cues of an ambush predator

Ambush predators provide more persistent cues of predation risk compared to coursing predators and are predicted to exert stronger effects on behaviour of their prey. We studied anti-predator responses of ungulates by means of camera traps to an olfactory cue (fresh scat) of an ambush predator, the Eurasian lynx ( Lynx lynx). Roe deer ( Capreolus capreolus) and red deer ( Cervus elaphus) both important prey species for lynx were not more vigilant when exposed to lynx scent, but reduced their visitation duration. Our results contrast with previously reported responses of red deer to scent from a coursing predator, the wolf ( Canis lupus), where only vigilance and foraging behaviour but not visitation duration changed in response to wolf scat. This indicates that ungulates are able to recognize the risk of predation from predators with differing hunting modes based on olfactory cues and adjust their anti-predatory behaviour.

Response of moose hunters to predation following wolf return in Sweden.

Background Predation and hunter harvest constitute the main mortality factors affecting the size and dynamics of many exploited populations. The re-colonization by wolves (Canis lupus) of the Scandinavian Peninsula may therefore substantially reduce hunter harvest of moose (Alces alces), the main prey of wolves. Methodology/Principal findings We examined possible effects of wolf presence on hunter harvest in areas where we had data before and after wolf establishment (n = 25), and in additional areas that had been continuously exposed to wolf predation during at least ten years (n = 43). There was a general reduction in the total number of moose harvested (n = 31,827) during the ten year study period in all areas irrespective of presence of wolves or not. However, the reduction in hunter harvest was stronger within wolf territories compared to control areas without wolves. The reduction in harvest was larger in small (500-800 km2) compared to large (1,200-1,800 km2) wolf territories. In areas with newly established wolf territories moose management appeared to be adaptive with regard to both managers (hunting quotas) and to hunters (actual harvest). In these areas an instant reduction in moose harvest over-compensated the estimated number of moose killed annually by wolves and the composition of the hunted animals changed towards a lower proportion of adult females. Conclusions/Significance We show that the re-colonization of wolves may result in an almost instant functional response by another large predator—humans—that reduced the potential for a direct numerical effect on the density of wolves’ main prey, the moose. Because most of the worlds’ habitat that will be available for future colonization by large predators are likely to be strongly influenced by humans, human behavioural responses may constitute a key trait that govern the impact of large predators on their prey.

Feeding under high risk of intraguild predation: vigilance patterns of two medium-sized generalist predators

Abstract To balance conflicting demands for food and safety from predation, foraging individuals trade off time between feeding and safety by vigilant behavior. We studied the behavior of red foxes (Vulpes vulpes) and pine martens (Martes martes) scavenging at carcasses of moose (Alces alces) killed by wolves (Canis lupus) in Sweden. Red foxes were observed visiting carcasses more often and at a higher frequency than pine martens, which restricted carcass use to certain habitats. Both species followed a similar daily and seasonal activity pattern. The seasonal peak of scavenging, in April for pine martens and April–May for red foxes, showed that remains of wolf-killed prey are likely an important food source for both of these species during reproduction. Pine martens displayed an overall higher level of vigilance and a lower level of feeding than red foxes. Vigilance by pine martens was affected by habitat, visibility, and vegetative cover at carcass sites. Pine martens did not display increased vigilance during time periods of high red fox activity and there was no effect of the time of day. Our study showed support for the importance of interspecific predation risk leading smaller predators to trade off foraging for increased vigilance, but habitat characteristics affected vigilance patterns more than the mere presence of a larger predator.

Mesopredator behavioral response to olfactory signals of an apex predator

Olfactory signals constitute an important mechanism in interspecific interactions, but little is known regarding their role in communication between predator species. We analyzed the behavioral responses of a mesopredator, the red fox (Vulpes vulpes), to an olfactory cue (scat) of an apex predator, the lynx (Lynx lynx) in Białowieża Primeval Forest, Poland, using video camera traps. Red fox visited sites with scats more often than expected and the duration of their visits was longer at scat sites than at control sites (no scat added). Vigilant behavior, sniffing and scent marking (including over-marking) occurred more often at scat sites compared to control sites, where foxes mainly passed by. Vigilance was most pronounced during the first days of the recordings. Red fox behavior was also influenced by foxes previously visiting scat sites. They sniffed and scent marked (multiple over-marking) more frequently when the lynx scat had been over-marked previously by red fox. Fox visits to lynx scats may be seen as a trade-off between obtaining information on a potential food source (prey killed by lynx) and the potential risk of predation by an apex predator.

Competition between apex predators? Brown bears decrease wolf kill rate on two continents

Trophic interactions are a fundamental topic in ecology, but we know little about how competition between apex predators affects predation, the mechanism driving top-down forcing in ecosystems. We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos). We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect. In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone. The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities.

Data to model risks for recolonizing wolves in Scandinavia through the integration of territory presence and human-driven mortalities

This dataset article describes the data and sources used to model risks for the recolonizing wolf (Canis lupus) in Sweden and Norway in the article “Integrated spatially-explicit models predict pervasive risks to recolonizing wolves in Scandinavia from human-driven mortality” (Recio et al., 2018). Presences on wolf territories were used to model the potential distribution of the species. Presences of human-driven mortalities including traffic collisions, culling (protective/defensive, and licensed hunting), and illegal killing (i.e. poaching) were used to model predictions on the distribution of these mortalities. Sources for the independent variables used for the models are also described.