Per Wegge

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

Abstract Northern Botswana and adjacent areas, have the worlds 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.

Predicting space use responses to habitat fragmentation: can voles Microtus oeconomus serve as an experimental model system (EMS) for capercaillie grouse Tetrao urogallus in boreal forest?

Abstract We found similarities in space use response by individual root voles Microtus oeconomus and capecaillie grouse Tetrao urogallus to habitat fragmentation. Male capercaillies and some male voles responded to a fine-grained fragmentation pattern by expanding their home ranges to include more than one habitat fragment. Breeding female voles belonging to a northern, aggresive strain spread out over single habiaat fragments (fission response) when the habitat was moderately coarse-grained. The same response was shown by lekking capercaillie males in the spring; as their spring lek habitat gradually became more coarse-grained due to logging, coalitions of neighbouring males dissolved, resulting in solitary displaying individuals. Breeding female voles belonging to a southern, docile strain and capercaillie males (in the non-breeding season) responded to a coarse-grained habitat fragmentation by congregating with highly overlapping home ranges on remaining habitat patches. Our results suggest that experimentally tractable species (e.g. voles) may be used as Experimental Model Systems (EMS) to predict responses by other wildlife species (such as capercaillie grouse) which are less amendale to experimentation.

Effects of trapping effort and trap shyness on estimates of tiger abundance from camera trap studies

Camera trapping has recently been introduced as an unbiased and practical method for monitoring tiger abundance. In a high density area in the Royal Bardia National Park in lowland Nepal, we tested this method by trapping very intensively within a 25 km2 area to determine the true number of animals in that area. We then tested the effect of study design by sub-sampling the data set using varying distances between trap stations and by reducing the number of trapping nights at each station. We compared these numbers with the density estimates generated by the capture–recapture models of the program CAPTURE. Both distance between traps and trapping duration greatly influenced the results. For example, increasing the inter-trap distance from 1 to 2.1 km and reducing the trapping duration per station from 15 to 10 nights reduced the number of tigers captured by 25%. A significant decrease in trapping rates during successive 5-night periods suggested that our tigers became trap-shy, probably because of the photo flash and because they detected the camera traps from cues from impression pads 50 m from the traps. A significant behavioural response was also confirmed by the program CAPTURE. The best capture–recapture model selected by the computer program (Mbh) gave precise estimates from data collected by the initial 1 km spacing of traps. However, when we omitted data from half the number of traps, thus decreasing the sampling effort to a more realistic level for monitoring purposes, the program CAPTURE underestimated the true number of tigers. Most probably, this was due to a combination of trap shyness and the way the study was designed. Within larger protected areas, total count from intensive, stratified subsampling is suggested as a complementary technique to the capture–recapture method, since it circumvents the problem of trap shyness.

Park-people relationships : the case of damage caused by park animals around the Royal Bardia National Park, Nepal

Crop damage and livestock predation were a serious problem in three Village Development Committees (VDCs) situated adjacent to the Southwestern Part of the Royal Bardia National Park. The seriousness of crop and livestock losses varied considerably with the distance from the Parks border and the specific location of farms. This was explained by the variations in the distribution of animal wildlife inside the Park, the presence of natural and Man-made barriers, the availability of forested areas outside the Park, and the agricultural cropping pattern. Adjacent to the section of the Park with the highest animal densities, crop losses varied from 47% for Lentil to 24% for Wheat. Farther away, the extent of crop losses was reduced. In the ‘Far’ zone situated 2–8 km from the Park, only 3% of the Paddy was reported lost. Two wildlife species, Chital and Wild Boar, were responsible for roughly half of the total damage to crops by animals. Damage from a newly-introduced population of Rhinoceros unicornis was increasing, with Paddy (Rice) and Lentil the crops most affected by that species. The economic value of livestock loss to wild predators was estimated to be two percent of the value of total crop losses. The estimated value of grasses harvested by local villagers inside the Park, seen as ‘compensation’ for crop losses and denial of access to traditional resources, constituted only 10% of the total economic loss from crop losses and livestock predation.

Size and spacing of capercaillie leks in relation to social behavior and habitat

SummarySpring territories of 17 adult capercaillie (Tetrao urogallus L.) cocks were 10–79 ha in extent; they varied inversely in size with the relative proportion of mature forest within them. The number of resident cocks at leks increased with the amount of mature forest within a 1 km radius of each lek center. Leks in two areas (n=46) were regularly spaced with mean distances to nearest neighbors of 1.98 and 2.07 km, corresponding to the territorial space occupied by adult cocks of adjoining leks. In one area with intensive logging, interlek distance increased with decreasing amounts of mature forest between them. Spring home ranges of 18 adult females averaged 51.3 ha±8.2 SE. The spatial relationships did not fit recent models of interlek spacing based on female spacing behavior. Instead, the results suggested that spacing of leks may be related to the territorial requirements of males.

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.

Do tigers displace leopards? If so, why?

We investigated predictions concerning the competitive relationships between tigers Panthera tigris and leopards Panthera pardus in Bardia National Park, Nepal, based on spatial distributions of scats and territorial markings (sign), analyses of scat content and census of wild ungulate prey. Medium-sized ungulates, in particular chital Axis axis, was the main food of both predators, but leopards consumed significantly larger proportions of domestic animals, small mammals, and birds than tigers. Tiger sign were never found outside the park, while leopard sign occurred both inside and outside, and were significantly closer to the park border than tiger sign. Significantly higher prey densities at locations of tiger sign than that of leopards were mainly due to a preference of the latter species for the park border areas. Our results imply that interference competition––and not competition for food––was a limiting factor for the leopard population, whose distribution was restricted to the margins of the tiger territories. We suggest that the composition of the prey base is a key factor in understanding the different results and interpretations reported in studies on tiger/leopard coexistence. There are two potential mechanisms that link interference competition and prey: (1) low abundance of large ungulate prey decreases foraging efficiency of tigers, leading to increased energetic stress and aggression towards leopards; and (2) increased diet overlap due to scarcity of large prey leads to increased encounter rates and increased levels of interference competition.

Dry season diets of sympatric ungulates in lowland Nepal: competition and facilitation in alluvial tall grasslands

Based on microhistological analyses of faecal material, we compared the early dry season diets of greater one-horned rhinoceros Rhinoceros unicornis, swamp deer Cervus duvauceli and hog deer Axis porcinus, which inhabit the same alluvial grassland habitat complex in lowland Nepal. Their diets were quite similar, both at the forage category level and within subcategories of graminoids and woody plants. Early successional tall grasses, especially Saccharum spontaneum, were the dominant food of all three species, underlining the key role of the threatened alluvial floodplains in large mammal conservation in South Asia. The two deer species ate significantly more graminoids (>66.5%) than did rhino (45.5%), and although they did not differ in proportions of graminoids, swamp deer ate significantly more late successional tall grasses (Narenga porphyrocoma and Themeda spp.) and short grasses (mainly Imperata cylindrica) than hog deer. The two deer consumed almost equal proportions of woody browse (ca. 10%), significantly less than that of rhino (33.0%). The prediction of the Jarman–Bell hypothesis, that large-bodied herbivores are less selective and subsist on lower quality graminoids than smaller ruminants, was not supported by the data. Based on this and previous studies in the same area we propose a conceptual model where the larger megaherbivores (rhino and elephant Elephas maximus) facilitate the smaller swamp deer and hog deer during the monsoonal growing season, while the smaller and more selective deer species outcompete the larger during the dry season when food is more limited. Owing to the all-year sprouting ability of S. spontaneum, facilitation may occur also in the dry season with low numbers of megaherbivores, thus accentuating competitive exclusion at higher deer densities.

Spacing and activity patterns of leopards Panthera pardus in the Royal Bardia National Park, Nepal

Abstract Space use and activity of radio-collared leopards Panthera pardus (two adult males and one adult female) were monitored during 3–25 months in a prey-rich part of the Royal Bardia National Park, Nepal. Annual home ranges of the two males were 47 and 48 km2 and had an overlap of only 7%, whereas the overlap between the females home range (17 km2) and that of one of the males was 56%. The range sizes were larger than reported from other studies in southeast Asia, but much smaller than some ranges in Africa. When comparing different studies, the sexual difference in range size increased significantly with increasing average range size. Thus, the cost by males of traversing large home ranges is probably not a determinant factor in shaping leopard communities. The females seasonal home ranges (5.2 and 6.6 km2) were smallest during the seasons when her cubs were less than six months of age. She moved her home range closer to agricultural fields during the season when the abundant and important prey axis deer Axis axis visits these areas most frequently. No such pattern was detected among the two males. Instead they frequented human settlements throughout the year, probably in order to hunt easily accessible domestic animals. Home ranges in similar seasons in consecutive years overlapped more (female = 64%, male = 75%) than ranges in different seasons in the same year (female = 38%, male = 64%). Intensive tracking sessions of 24 hours revealed that the diel activity levels of the two sexes were similar (female: 62.3%, males: 62.6%). However, their patterns of activity were different as the males moved mainly at night (day: 1,582 m, night: 5,244 m) and the female moved similar distances day and night (day: 2,381 m, night: 2,698 m). The female may have restricted her movement at the time when conspecific males were likely to be active in order to protect her cubs from infanticide. The males moved in a more linear manner than the female, and the linear distances between radio locations from consecutive days differed significantly between the sexes (male: 3,324 m, female: 881 m), but the actual distances moved during the 24-hour cycles were fairly similar (male: 6,826 m, female: 5,079 m).

The effects of cutting and burning on grass quality and axis deer ( Axis axis ) use of grassland in lowland Nepal

Man-made grasslands dominated by Imperata cylindrica (L.) Beauv. in forested areas of lowland Nepal are commonly cut and/or burned annually. Changes in grass forage quality following different treatments of cutting and burning and axis deer ( Axis axis ) response to such habitat manipulations were investigated. Samples of matured grass were collected in December 1990, February and April 1991 from three experimental sites: cut, burned, cut-and-burned. Four locations on cut-and-burned grassland were repeatedly sampled at 12-d intervals from January to April 1992. Numbers of axis deer were recorded during the dry season of 1991/1992 on grassland plots receiving the following treatments: cut, cut-and-burned, and uncut/unburned (controls). Based on grass quality differences between December and February and between December and April, cut-and-burned treatments gave the greater increase in forage quality. N was significantly higher on cut-and-burned plots than on cut plots both in February and in April, while Na, K and P was significantly higher in February. On plots cut-and-burned in January, Ca concentrations were relatively low while the P content fell below required levels for domestic stock towards the end of the dry season in April. Na concentrations were below the minimum required levels for both domestic and wild ruminants during the whole period. When an entire grassland was cut, deer density increased gradually. When the same area was subsequently burned, the daily deer density increased much more rapidly. Axis deer preferred burned plots compared to plots neither cut nor burned and to cut plots. Plots burned in late February had higher densities of axis deer than plots burned 1.5 mo earlier. When nearby recently burned plots were available, deer density was reduced on plots burned earlier.