Annual variation in breeding success in boreal forest grouse: Four decades of monitoring reveals bottom-up drivers to be more important than predation

Knowledge of the temporal variation in reproductive success and its key driving factors is crucial in predicting animal population persistence. Few studies have examined the effects of a range of explanatory factors operating simultaneously on the same population over a long period. Based on 41 years of monitoring (1979–2019), we tested prevailing hypotheses about drivers of annual variation in breeding success in two sympatric species of boreal forest grouse—the capercaillie (Tetrao urogallus) and the black grouse (T. tetrix)—in a 45 km² boreal forest landscape. From counts in early August, we measured breeding success (chicks/hen) along with potential determining factors. We formulated five main hypotheses on causes of variation (hen condition, chick weather, chick food, predation, demographic characteristics) and derived 13 associated explanatory variables for analysis. We first tested the five hypotheses separately and then used model selection (AICc) to rank the best predictive models irrespective of hypotheses. Lastly, we used path analysis to illuminate potential causal relationships. Barring demographic characteristics, all hypotheses were supported, most strongly for chick food and predation. Among predictor variables, chick food (insect larvae and bilberry fruit crops), vole and fox abundances, the winter‐NAO index, and temperature after hatching, had the strongest effect sizes in both species. Precipitation after hatching had no detectable effect. Model selection indicated bottom‐up factors to be more important than predation, but confounding complicated interpretation. Path analysis suggested that the high explanatory power of bilberry fruiting was due not only to its direct positive effect on chick food quality but also to an indirect positive effect on vole abundance, which buffers predation. The two components of breeding success—proportion of hens with broods and number of chicks per brood—were uncorrelated, the former having the strongest effect. The two components had different ecological correlates that often varied asynchronously, resulting in overall breeding success fluctuating around low to moderate levels. Our study highlights the complexity of key explanatory drivers and the importance of considering multiple hypotheses of breeding success. Although chick food appeared to equal or surpass predation in explaining the annual variation in breeding success, predation may still be the overall limiting factor. Comparative and experimental studies of confounded variables (bilberry fruiting, voles, and larvae) are needed to disentangle causes of variation in breeding success of boreal forest grouse.

Multiple factors influence local perceptions of snow leopards and Himalayan wolves in the central Himalayas, Nepal

An understanding of local perceptions of carnivores is important for conservation and management planning. In the central Himalayas, Nepal, we interviewed 428 individuals from 85 settlements using a semi-structured questionnaire to quantitatively assess local perceptions and tolerance of snow leopards and wolves. We used generalized linear mixed effect models to assess influential factors, and found that tolerance of snow leopards was much higher than of wolves. Interestingly, having experienced livestock losses had a minor impact on perceptions of the carnivores. Occupation of the respondents had a strong effect on perceptions of snow leopards but not of wolves. Literacy and age had weak impacts on snow leopard perceptions, but the interaction among these terms showed a marked effect, that is, being illiterate had a more marked negative impact among older respondents. Among the various factors affecting perceptions of wolves, numbers of livestock owned and gender were the most important predictors. People with larger livestock herds were more negative towards wolves. In terms of gender, males were more positive to wolves than females, but no such pattern was observed for snow leopards. People’s negative perceptions towards wolves were also related to the remoteness of the villages. Factors affecting people’s perceptions could not be generalized for the two species, and thus need to be addressed separately. We suggest future conservation projects and programs should prioritize remote settlements.

The alternative prey hypothesis revisited: Still valid for willow ptarmigan population dynamics

The alternative prey hypothesis predicts that the interaction between generalist predators and their main prey is a major driver of population dynamics of alternative prey species. In Fennoscandia, changes in climate and human land use are assumed to alter the dynamics of cyclic small rodents (main prey) and lead to increased densities and range expansion of an important generalist predator, the red fox Vulpes vulpes. In order to better understand the role of these potential changes in community structure on an alternative prey species, willow ptarmigan Lagopus lagopus, we analyzed nine years of population census data from SE Norway to investigate how community interactions affected their population dynamics. The ptarmigan populations showed no declining trend during the study period, and annual variations corresponded with marked periodic small rodent peaks and declines. Population growth and breeding success were highly correlated, and both demographic variables were influenced by an interaction between red fox and small rodents. Red foxes affected ptarmigan negatively only when small rodent abundance was low, which is in accordance with the alternative prey hypothesis. Our results confirm the important role of red fox predation in ptarmigan dynamics, and indicate that if small rodent cycles are disrupted, this may lead to decline in ptarmigan and other alternative prey species due to elevated predation pressure.

Climate change and bird reproduction: warmer springs benefit breeding success in boreal forest grouse

Global warming is predicted to adversely affect the reproduction of birds, especially in northern latitudes. A recent study in Finland inferred that declining populations of black grouse, Tetrao tetrix, could be attributed to advancement of the time of mating and chicks hatching too early—supporting the mismatch hypothesis. Here, we examine the breeding success of sympatric capercaillie, T. urogallus, and black grouse over a 38-year period in southeast Norway. Breeding season temperatures increased, being most pronounced in April. Although the onset of spring advanced nearly three weeks, the peak of mating advanced only 4–5 days. In contrast to the result of the Finnish study, breeding success increased markedly in both species (capercaillie: 62%, black grouse: 38%). Both brood frequency and brood size increased during the study period, but significantly so only for brood frequency in capercaillie. Whereas the frequency of capercaillie broods was positively affected by rising temperatures, especially during the pre-hatching period, this was not the case in black grouse. Brood size, on the other hand, increased with increasing post-hatching temperatures in both species. Contrary to the prediction that global warming will adversely affect reproduction in boreal forest grouse, our study shows that breeding success was enhanced in warmer springs.

Snow Leopard and Himalayan Wolf: Food Habits and Prey Selection in the Central Himalayas, Nepal

Top carnivores play an important role in maintaining energy flow and functioning of the ecosystem, and a clear understanding of their diets and foraging strategies is essential for developing effective conservation strategies. In this paper, we compared diets and prey selection of snow leopards and wolves based on analyses of genotyped scats (snow leopards n = 182, wolves n = 57), collected within 26 sampling grid cells (5×5 km) that were distributed across a vast landscape of ca 5000 km² in the Central Himalayas, Nepal. Within the grid cells, we sampled prey abundances using the double observer method. We found that interspecific differences in diet composition and prey selection reflected their respective habitat preferences, i.e. snow leopards significantly preferred cliff-dwelling wild ungulates (mainly bharal, 57% of identified material in scat samples), whereas wolves preferred typically plain-dwellers (Tibetan gazelle, kiang and argali, 31%). Livestock was consumed less frequently than their proportional availability by both predators (snow leopard = 27%; wolf = 24%), but significant avoidance was only detected among snow leopards. Among livestock species, snow leopards significantly preferred horses and goats, avoided yaks, and used sheep as available. We identified factors influencing diet composition using Generalized Linear Mixed Models. Wolves showed seasonal differences in the occurrence of small mammals/birds, probably due to the winter hibernation of an important prey, marmots. For snow leopard, occurrence of both wild ungulates and livestock in scats depended on sex and latitude. Wild ungulates occurrence increased while livestock decreased from south to north, probably due to a latitudinal gradient in prey availability. Livestock occurred more frequently in scats from male snow leopards (males: 47%, females: 21%), and wild ungulates more frequently in scats from females (males: 48%, females: 70%). The sexual difference agrees with previous telemetry studies on snow leopards and other large carnivores, and may reflect a high-risk high-gain strategy among males.

Guild composition and habitat use of voles in 2 forest landscapes in south-eastern Norway

It is widely believed that intensive forestry has influenced small mammal population dynamics, and thereby the entire mammalian community in Fennoscandian boreal forests. The nature of these impacts on the different species is subject to debate. We live-trapped voles between 2006 and 2009 in 2 commercially harvested forests in south-eastern Norway. We investigated the variation in vole abundance among habitat types (e.g. mature forest and clear-cut) and the hypothesis that graminivorous species such as field voles (Microtus agrestis L.) benefit from clear-cuts at the expense of forest dwellers (i.e. the bank vole, Myodes glareolus Schreb.), using fine-scale descriptors of the ground vegetation. We could not find support for the hypothesis that field voles show a preference for clear-cuts, and their overall abundance was low, while bank voles were the dominant species in all habitat types, including clear-cuts in the peak and pre-peak years. We found a positive association between bank vole abundance and bilberry (Vaccinium myrtillus L.) availability rather than a specific habitat type. Low field vole density in clear-cuts might be due to variation in local productivity and ground vegetation as well as to large variation in the species temporal dynamics. The latter is particularly associated with the widespread decline of field voles in Scandinavia. Logging has the potential to negatively affect bank vole population dynamics because of the negative effect on bilberry development.

Size and spacing of grouse leks: comparing capercaillie (Tetrao urogallus) and black grouse (Tetrao tetrix) in two contrasting Eurasian boreal forest landscapes

Capercaillie ( Tetrao urogallus L., 1758) and black grouse ( Tetrao tetrix L., 1758 (= Lyrurus tetrix (L., 1758))) are two sympatric Eurasian lekking grouse species that differ markedly in habitat affinities and social organization. We examined how size and spacing of leks in pristine (Russia) and managed (Norway) forests were related to habitat and social behavior. Leks of both species were larger and spaced farther apart in the pristine landscape. Capercaillie leks were regularly spaced at 2–3 km distance, increasing with lek size, which in turn was positively related to the amount of middle-aged and older forests in the surrounding area. Black grouse leks were irregularly distributed at shorter distances of 1–2 km, with lek size explained by the size of the open bog arena and the amount of open habitat in the surroundings. At the landscape scale, spatial distribution of open bogs and social attraction among male black grouse caused leks to be more aggregated, whereas mutual avoidance in male capercaillie caused leks to be spaced out. In the pristine landscape, large-scale and long-term changes in forest dynamics owing to wildfires, combined with an aggregated pattern of huge bog complexes, presumably provide both grouse species with enough time and space to build up bigger lek populations than in the managed landscape.

Predicting spacing behavior and mating systems of solitary cervids: A study of hog deer and Indian muntjac

This study investigates the validity of current theory for predicting ecological and allometric effects on space use, social structure and mating systems of poorly known solitary cervids, based on a comparative analysis of radio-telemetry data on hog deer Axis porcinus (N=32) and Indian muntjac Muntiacus muntjak (N=28). The larger and sexually size-dimorphic hog deer inhabit highly productive alluvial floodplains, where resource distribution is patchy and spatiotemporally unpredictable. As predicted for this species, site fidelity was low and range sizes varied among sex and age groups and among seasons. Hog deer were probably non-territorial, as home range sizes seemed too large to be exclusive when taking into account their high population density. Extensive movements of adult males during the rut implied "roaming" as a mating strategy. The smaller, forest-dwelling and sexually size-monomorphic muntjacs inhabit a more uniform and stable habitat. As predicted, muntjacs exhibited higher site fidelity than hog deer, and no seasonal variations in home range sizes. Adults exhibited relatively large home range overlap, both inter- and intrasexually. Hence, strict territoriality did not occur, but their well-defined home ranges and high site fidelity indicated some form of site-specific dominance. In conclusion, habitat characteristics were appropriate predictors of home range sizes and site fidelity. Body mass appeared to be a suitable predictor of intraspecific patterns in space use but a poor predictor of interspecific patterns, probably due to a confounding effect of habitat productivity.

Capercaillie broods in pristine boreal forest in northwestern Russia: the importance of insects and cover in habitat selection

Capercaillie (Tetrao urogallus L., 1758), the largest and most size-dimorphic species of grouse, is decreasing in number throughout its man-modified range in the boreal forests of the Palaearctic. Poor reproduction owing to direct and indirect effects of commercial forestry is considered a main cause of the decline. We studied brood habitats in a pristine forest in northwestern Russia to identify key elements in habitat selection in the natural environment of this species. We monitored the movement of 10 radio-marked broods during their first 7 weeks of life, and compared the abundance of insects and cover at their locations (N = 120) with nearby random control sites. The broods preferentially used moist spruce forest and the insect-rich herb spruce forest, but were most often located in the more abundant vaccinium spruce forest, which was richest in bilberry (Vaccinium myrtillus L.) and associated lepidopteran larvae. Brood locations were consistently richer in insects than random controls in 3 of the 4 habitat types studied. The most pronounced difference was in the density of lepidopteran larvae, a food source known to form an important part of the diet of young capercaille chicks. Broods continued to select insect-rich sites throughout the 7 week age period; in the preferred moist spruce forest, larval abundance increased at brood locations, while it remained constant at control sites. Compared to the distribution of insects, cover did not appear to be as an important determinant of brood habitat selection, possibly because the structural characteristics were rather similar among the most widely used habitat types. Shrub cover tended to be higher at brood locations than at controls, whereas vertical cover along the ground was not different. This relationship to cover factors may reflect an adaptation to avoid predation by goshawk (Accipiter gentilis (L., 1758)), the most important predator of grouse in this pristine boreal forest.

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.

The return of the giants: ecological effects of an increasing elephant population

Northern Botswana and adjacent areas, have the world's largest population of African elephant (Loxodonta africana). However, a 100 years ago elephants were rare following excessive hunting. Simultaneously, ungulate populations were severely reduced by decease. The ecological effects of the reduction in large herbivores must have been substantial, but are little known. Today, however, ecosystem changes following the increase in elephant numbers cause considerable concern in Botswana. This was the background for the "BONIC" project, investigating the interactions between the increasing elephant population and other ecosystem components and processes. Results confirm that the ecosystem is changing following the increase in elephant and ungulate populations, and, presumably, developing towards a situation resembling that before the reduction of large herbivores. We see no ecological reasons to artificially change elephant numbers. There are, however, economic and social reasons to control elephants, and their range in northern Botswana may have to be artificially restricted.

Spacing behaviour and habitat use of axis deer (Axis axis) in lowland Nepal

A total of 17 axis deer (Axis axis) (12 females, 5 males) were radio-instrumented in Bardia National Park in lowland Nepal, and 1921 locations of females and 605 locations of males were obtained during the 2-year study period. Both the annual home ranges (135 ± 33 and 204 ± 38 (SD) ha for females and males, respectively) and the seasonal home ranges were quite small compared with those reported in another study in Nepal. We present evidence that this difference is due to a more fine-grained habitat mosaic in Bardia. Males used larger areas than females in the monsoon and the hot part of the dry season. The deer were sedentary, with a mean seasonal home range overlap between 49 and 86%, and seasonal occupancy centres were all located less than 1300 m apart. Mean seasonal home range size (68 and 110 ha for females and males, respectively) was smallest in the cool part of the dry season. The rutting period did not seem to have any major effect on the ranging behaviour, as neither males nor females increased home range size from the pre-rut to the rutting period. The deer used riverine forest preferentially during the cool-dry and hot-dry seasons, whereas sal forest was the preferred habitat during the monsoon and the cool-dry season. Grasslands were preferentially utilized by females at night during the hot-dry season, presumably because of improved forage quality following cutting and burning. Males were more associated with riverine and sal forest than were females, while females used grassland areas more than males did.

Spacing and habitat use of capercaillie during summer

We radio-tracked 52 capercaillie males and 21 broodless females during June, July, and August, 1979–1986, in a 100-km2 coniferous forest in central Scandinavia. After display activity ceased in early June, 77% of adult males made distinct movements, averaging 1.5 km, from lek territories to summer ranges. A similar movement was made by 48% of the females after loss of nest or brood. Males were now nonterritorial, and lived solitarily in overlapping home ranges averaging 170 ha. In June and July, they used successional stages in proportion to availability, but in August they preferred old, natural forest. Females, having home ranges averaging 103 ha, commonly formed small social groups of two to four individuals. They preferred young plantations throughout summer, and also preferred denser habitats than males. Both sexes returned to the same summer ranges in consecutive years. Home ranges of both sexes were distributed in a clumped spacing pattern. This can be explained by preference for patchily distributed habitat types in males, and habitat preference and sociality in broodless females.