Torstein Storaas

Supplemental feeding of migratory moose Alces alces: forest damage at two spatial scales

Landowners in southeast Norway have supplied moose Alces alces with ensilaged bales of hay for up to eight winters. The incentive has been to limit migratory movements into heavily trafficated winter areas and away from young forest plantations. In this article, we report on landscape characteristics that increase the use of feeding stations, and on how browsing activity on Scots pine Pinus sylvestris twigs as well as leader stems of both pine and Norway spruce Picea abies was associated with distance to feeding stations at two different spatial scales: 1) at a local scale we sampled data from 50 m2 observational plots up to 200 m from the feeding stations, and 2) at a regional scale we sampled data at all available young forest plantations up to 7 km from a feeding station. The probability that a feeding station was used increased towards the bottom of side valleys. The frequency of use of feeding stations increased annually, with increasing distance to other feeding stations, and with increasing distance to the more populated main valley. Moose-induced browse damage was extensive at proximate distances (< 200 m) to feeding stations, decreased to a minimum at 1–2 km, and increased slightly again at 3–7 km distance from less intensely used feeding stations. Indices of moose activity distribution (i.e. piles of faecal pellets) resembled browsing activity.

THE EFFECT OF SCENT‐MARKING, FOREST CLEARING, AND SUPPLEMENTAL FEEDING ON MOOSE‐TRAIN COLLISIONS

Abstract We analyzed how the application of scent-marking, forest clearing, and supplemental feeding correlated with the number of moose (Alces alces)–train collisions along the most vulnerable railroad stretch in Norway. Data on 1,045 collisions has been compiled for 18 years since 1985, and remedial actions have occurred during various periods since 1990. We used sections of the rail line where remedies had never been applied as control sections to estimate the expected number of collisions per year and per km. In this way, we took into account the yearly variation in the number of accidents by using the difference between the actual number of accidents and the expected number of accidents as our response variable. We compared the difference between periods when remedies were applied to periods without any remedy. We found a general 46% decrease in the number of accidents during years with a remedy compared to what would have been expected the same years without any remedy. Forest clearing and supplemental feeding seem to be reliable ways of reducing the number of collisions. Scent was only applied for short distances in a few years, and the beneficial effects we observed were questionable. We conclude that mitigative efforts may substantially reduce accidental mortality in moose populations if applied for long distances. We discuss the economics of game-vehicle collisions by performing a simple calculation to visualize the need for a bio-economic approach to the problem.

Detection of forest grouse by mammalian predators: A possible explanation for high brood losses in fragmented landscapes

We used hunting dogs and man to simulate the searching for nests and broods of forest grouse, i.e. capercaillie Tetrao urogallus and black grouse Tetrao tetrix, by mammalian predators. Our aim was to find out if and how forest fragmentation affects the searching efficiency of predators. In total, we found 73 capercaillie and 35 black grouse nests and 20 young capercaillie broods. We calculated that a mammalian predator will detect a capercaillie nest if closer than 1.6 m (95% C.I.: 0.7 - 2.2), a black grouse nest if closer than 1.1 m (95% C.I.: 0.8 - 1.6), and a capercaillie brood if closer than 39 m (95% C.I.: 17 - 89). Nests were distributed in all habitat types, whereas broods were restricted to specific brood habitats. Due to this and the difference in the detection radius between nests and broods, we estimated that the predator gain of searching for broods in brood habitat is about 80 times higher than the gain of searching for nests which are situated in all habitat types in our study area. As young broods concentrate in highly restricted habitats, the predator gain of searching for broods increases exponentially with the loss of brood habitat, whereas it decreases linearly with increasing nest predation. We discuss this mechanism as a possible process explaining the observed decline in capercaillie populations in fragmented forests and consider its implications for grouse management.

Activity patterns of predator and prey: a simultaneous study of GPS-collared wolves and moose

This is the postprint version of the article published in Animal behaviour. You can find the published article here: http://dx.doi.org/doi:10.1016/j.anbehav.2010.11.011

Reproductive success and failure: the role of winter body mass in reproductive allocation in Norwegian moose

A life history strategy that favours somatic growth over reproduction is well known for long-lived iteroparous species, especially in unpredictable environments. Risk-sensitive female reproductive allocation can be achieved by a reduced reproductive effort at conception, or the subsequent adjustment of investment during gestation or lactation in response to unexpected environmental conditions or resource availability. We investigated the relative importance of reduced investment at conception compared with later in the reproductive cycle (i.e. prenatal, perinatal or neonatal mortality) in explaining reproductive failure in two high-density moose (Alces alces) populations in southern Norway. We followed 65 multiparous, global positioning system (GPS)-collared females throughout the reproductive cycle and focused on the role of maternal nutrition during gestation in determining reproductive success using a quasi-experimental approach to manipulate winter forage availability. Pregnancy rates in early winter were normal (≥0.8) in all years while spring calving rates ranged from 0.4 to 0.83, with prenatal mortality accounting for most of the difference. Further losses over summer reduced autumn recruitment rates to 0.23–0.69, despite negligible predation. Over-winter mass loss explained variation in both spring calving and autumn recruitment success better than absolute body mass in early or late winter. Although pregnancy was related to body mass in early winter, overall reproductive success was unrelated to pre-winter body condition. We therefore concluded that reproductive success was limited by winter nutritional conditions. However, we could not determine whether the observed reproductive allocation adjustment was a bet-hedging strategy to maximise reproduction without compromising survival or whether females were simply unable to invest more resources in their offspring.

Use of Medetomidine-Ketamine and Atipamezole for Reversible Immobilization of Free-ranging Hog Deer (Axis porcinus) Captured in Drive Nets

A combination of 0.05 mg/kg medetomidine and 1.5 mg/kg ketamine was used to immobilize nine adult free-ranging hog deer (Axis porcinus) captured in drive nets in the Royal Bardia National Park, Nepal, 22–23 February 2000. The drugs were administered intramuscularly from separate syringes and the mean time (±SD) to complete immobilization was 4.6±1.0 min. Muscle relaxation was good and no major clinical side effects were seen. Mean values for physiologic parameters, recorded at 10–12 and 18–20 min after drug administration, were 40.6±0.5 and 41.1 ±0.6 C, 87±5 and 84±4%, 107±16 and 113±16 beats/min, and 46±9 and 40±8 breaths/min for rectal temperature, SpO2, pulse rate, and respiratory rate, respectively. All animals received 0.25 mg/ kg atipamezole intramuscularly 20–22 min after administration of medetomidine-ketamine and the mean time to coordinated running was 4.8±0.8 min. All animals survived for at least 5 mo post-capture. To reduce stress and to facilitate handling, medetomidine–ketamine and atipamezole are recommended for reversible immobilization of free-ranging hog deer captured in drive nets.

Hog deer Axis porcinus need threatened tallgrass floodplains: a study of habitat selection in lowland Nepal

In Asia, subtropical tall grasslands and their associated fauna are mostly confined to the floodplains of the large rivers draining the Himalayan range. In recent decades, cultivation and hydroelectric dam construction have severely reduced their spatial abundance. During 1998–2000, we conducted a detailed study of the habitat use of hog deer, Axis porcinus, an important prey species of tiger, Panthera tigris, in the floodplains of the large Karnali river in Royal Bardia National Park, Nepal. Strong preference for tall grass and avoidance of the successional stages following riparian forests throughout the year was revealed by analyses of tracking data from 18 radio-collared deer and from density estimates from block counts (n = 46) in different habitat types. Continuously strong selection for tall grass despite the reduced availability of this habitat type during the monsoonal flooding indicated an insignificant effect of density-dependent factors in habitat selection. Reduced availability of cover following traditional cutting and burning of the tall grasslands by local villagers did not produce changes in habitat use or an increase in daily movements, indicating an absence of trade-offs between habitat preference for food and for predator avoidance. By regulating fluvial action, hydroelectric power development will lead to the loss of tall grasslands due to accelerated secondary succession, which will therefore adversely affect the viability of local populations.

Three approaches to estimate wolf Canis lupus predation rates on moose Alces alces populations

We employed three different methods to estimate predation rates on moose in a newly colonized wolf territory in Norway. In the first two methods, we estimated predation rates based on the difference in calf/cow ratios outside and inside the wolf pack territory from (1) hunter observations and (2) aerial surveys. In the last method, (3) we estimated loss of calves of radio-collared cows inside and outside the wolf pack territory. The difference in mortality rates estimated between the area subject to predation and the area outside the wolf pack territory essentially constitutes the additive component of predation. We also tested the sensitivity of violating the assumptions of methods 1 and 2 related to equal fecundity and mortality because of other factors than predation inside and outside the wolf pack territory. Predation rates varied considerably between years and methods used, with hunter observations (method 1) giving the lowest and aerial surveys (method 2) giving the highest estimates. Method 3 (radio telemetry) was the most direct assessment of predation and probably the best approach to estimate predation rates in moose. However, all three methods show the same yearly changes and may therefore be appropriate to question trends trough time or between areas.

Weight-related renesting in capercaillie Tetrao urogallus

In a population study during 1979–1988 at Varaldskogen in southeastern Norway, 234 capercaillie Tetrao urogallus nests and broods were classified as first nests or renests. Of the females that had their first nest depredated, 9–87% (mean 36%) renested. Over a 6-year period, autumn brood production increased from 30 to 38% due to renesting. Renesting is physically demanding for the females; the eggs in renests are fewer and smaller, and the females take more and longer recesses than when incubating first nests. All the females incubated their first nests till the eggs hatched or the nest was depredated. Two of the renesting females took more and longer recesses until they gave up their nests. The ability to renest seems to be weight-related, as yearling females, which weigh less than adult females, did not renest, and the weight of adult females on leks was highest in the two years when most renesting occurred. The female will renest if the nest is depredated during the first three days of incubation. Each of the following 19 days, all years combined, a mean of 26% of females who lost their nests renested. Capercaillie renesting was related to the vole cycle; it was highest in the year before the small rodents peaked and decreased through the vole crash and the year after.

Effects of harvesting regime on food availability and cover from predators in capercaillie (Tetrao urogallus) brood habitats

Abstract Capercaillie (Tetrao urogallus) broods prefer habitats that contain food for the chicks and cover against predators. During the summer 2005, in each of nine areas, three initially similar forest stands were examined: one was harvested by clear-cutting and one by selective cutting, while the last was uncut. Brood habitats in terms of food availability and cover from predators in old forest stands were compared with those in selectively cut and clear-cut stands. The selectively cut forest stands were more open, so the chicks may have been easier to detect by raptors. On the clear-cuts the preferred chick food, Lepidoptera larvae, was less abundant and the measurements suggest that the chicks were easier to detect. If the amount of available brood habitat positively influences chick survival, clear-cutting is likely to decrease chick survival. Selective cutting preserves food availability, but may increase predation by raptors.