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Tree rubbing or marking by bears has been observed throughout the northern hemisphere. Even so, this behaviour has rarely been studied. We documented 93 sites where grizzly bears Ursus arctos horribilis rubbed on 116 trees during 1986–1992, in the Yellowstone Ecosystem. We used logistic regression and information-based estimation and selection criteria to specify models that explained selection of sites and individual trees for rubbing by bears in our study area. The probability of rubbing peaked during May and June, the period of mating and moult, and declined thereafter. At the landscape level, grizzly bears selected for gentle south-facing slopes, forest/non-forest ecotones with sparse deadfall, and forest stands dominated by lodgepole pine Pinus contorta or Douglas-fir Pseudotsuga menziesii. Among the trees at sites where bears rubbed, we found strong selection for large diameters but no indication of selection for species. Rubbed trees were highly associated with travel routes likely used by bears, including game trails, recreation trails and forest edges. Rubbing was often oriented towards these likely travel routes. Short trails of entrenched pad-shaped marks leading up to rubbed trees were recorded at 58% of the sites where rubbing occurred. Contrary to reports of black bears Ursus americanus clawing and biting trees, we found shredded or bitten bark at only 9% of sites with rubbed or otherwise marked trees. Circumstantial evidence suggests that bears used trees primarily for rubbing their back and shoulders. Our findings are consistent with previous arguments that rubbing serves as a means of chemical communication.
Trapping records are often used to monitor long-term trends of small carnivore populations. However, many factors, not related to abundance, may affect capture rates. In this study, we examined whether trapper experience, trapping effort and trapping methods significantly affect capture rates of red fox Vulpes vulpes, stone marten Martes foina and pine marten M. martes. Data were collected from 58 trappers (35,774 trap-nights) in a 660-km2 study area during one trapping season. The main trapping methods used for foxes and martens with different types of traps were identified by multiple correspondence analyses on 424 trap sites. Generalised linear modelling showed that trapping methods, the length of time traps were set in the same place, trapper experience and the presence of captures in neighbouring trap sites significantly affect capture rates of foxes and martens. Given the high variability of capture rates among different combinations of these factors (0–3.4 captures/100 trap-nights for fox and 0.6–7.8 captures/100 trap-nights for martens), a separate trapping index should be calculated to detect trends in small carnivore populations.
Wolverine Gulo gulo populations have a low reproductive potential and are thus relatively sensitive to changes in survival rates. Consequently, knowledge about survival and mortality causes in juvenile wolverines is important for a sound management of the species. We estimated survival rates for juvenile wolverines and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993–2001. We monitored 80 radio-marked juvenile wolverines from May to February. Intraspecific predation was the most important cause of juvenile mortality and occurred during two periods. First, seven juveniles were killed in May-June when still altricial, i.e. infanticide. Second, four juvenile females were killed by conspecifics outside their mothers' territories after independence in August–September. The survival rate of radio-marked juveniles during May-February was 0.68. There was a strong tendency for survival to be lower during the summer when juveniles were altricial, than after they became independent. The estimates of survival rates and mortality causes provided by this study are important for the understanding of wolverine population dynamics. Currently, our data are too weak to suggest an explicit explanation for infanticide in spring/early summer. Still, in the light of the available information on wolverine life history and infanticide patterns in other species, we suggest two, not mutually exclusive, hypotheses to consider for further investigation: 1) males kill non-related juveniles to increase their reproductive success, and 2) females kill non-related juveniles to reduce competition for resources. In addition, attention should be given to the alternative hypothesis that infanticide in wolverines is non-adaptive. Finally, we suggest that independent juvenile females were killed by resident females in territorial defence.
Evolutionary theories based on adaptive modification of maternal investment are generally suggested to explain variation in offspring sex ratios, but general concordance with empirical data is rare. Recently, factors beyond the control of the mother, such as density and climate, were reported to affect offspring sex ratios, and the extrinsic modification (EM) hypothesis has been advanced to explain such variation. The EM hypothesis states that offspring sex ratios in sexually dimorphic vertebrates may vary with extrinsically induced changes in maternal condition during pregnancy. We investigated sex ratio variation and inter-cohort calf live weight variation in 5,509 reindeer Rangifer tarandus calves during an eight-year period. Using separate models, we also tested whether offspring sex ratio covaried with density, and, respectively, summer weather before conception and winter weather (measured by the North Atlantic Oscillation (NAO)) when calves were in utero. Offspring sex ratios in mid-July differed from parity only in one year. Calf live weight varied among cohorts and males were heavier than females. The proportion of male calves in the herd decreased significantly with an increasing NAO index when calves were in utero. Density in the year of birth only affected calf sex ratios by increasing the negative effects of the NAO index. The proportion of males in the herd also declined with increasing summer temperature, summer precipitation, and density in the year of conception, suggesting potential for pre-conception environmental effect. Because the reported environmental variables affected negatively the proportion of male calves in the herd, we suggest that their effects may be associated with nutritional stress caused to the mother before conception, which have not been shown previously, and during pregnancy. Evidence of extrinsic sex ratio adjustment was conclusive and our findings therefore support the EM hypothesis of sex ratio variation.
We developed a mathematical model to quantify and compare the impact of different forms of wildlife harassment, and applied it to compare the effects of hikers and paragliders on the feeding time and area of chamois Rupicapra rupicapra, considering differences between hikers and paragliders in terms of their prevalence and behaviour. Although many more hikers than paragliders visited the study area, the impact of paragliders was much stronger. With increasing paraglider traffic, the effects would steeply increase, whereas the effects of hikers approached an asymptote. With modification of input values and/or parameters, the model can be applied to other species, to compare the effects of other forms of wildlife harassment, and to simulate effects of changing conditions such as habituation of the animals or changes in the daily or spatial pattern of occurrence of tourism.
On 15 July 2000, a pod of about 80 long-finned pilot whales Globic ephala melas was driven to the coast at Sandavágur, the Faroe Islands (62.055°N, 7.157°W) for the purpose of tagging selected whales with satellite-linked radio transmitters. A transmitter was attached to the anterior flank of the dorsal fin of four beached whales. After the tagging, all four whales were reunited with their pod and the entire pod was driven to sea. The positions of three of the four whales were tracked (one for a period of 47 days) and the results show that the whales separated after a few days and eventually went in different directions. After 10 days, two of the whales were observed together in a pod, and after 19 days two of the whales were located at positions determined to be within 2.3 km of each other. The whales showed a strong affinity for the deep water off the continental shelf. The sex and relatedness of the four, tagged whales were determined from skin biopsies. The tagged whales comprised one adult female with one juvenile in puberty, possibly her male offspring, and two adult males, one of which could be the offspring or the sibling of the female. The swimming speed of the whales was estimated at 0.2–14.5 km/hour, and they travelled average distances of 70–111 km/24 hours with a maximum of 200 km in 24 hours. Considering the mobility of the whales, it seems likely that the catches that occur at the Faroe Islands are recruited from a larger area in the North Atlantic than previously presumed. This suggests that the whales are taken from a larger population than that estimated from coastal areas around the Faroe Islands, hence increasing the probability that the harvest is sustainable.
It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species. In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated here can modulate the dynamic properties of the population in a way not predicted by linear models. We argue that the behaviour of exploited populations and the role of harvesting can only be understood if we identify and understand the interplay of endogenous and exogenous components of population dynamics.
Census data from a eutrophic lake collected in 1987–1999 were used to study nesting and breeding success in mallards Anas platyrhynchos. In each year there were 6–19 pair counts and 13–34 brood counts. The maximum combined count of single males and pairs (i.e. on any day in any of three census periods in May) provided the best fit with subsequent estimates of breeding success. Nesting success (average brood:pair ratio = 0.52), brood size of older ducklings (mean = 5.7) as well as fledgling success (2.86 juveniles per nesting pair) were higher than in many previous mallard studies. Per capita brood production as well as per capita fledgling production was negatively density dependent, but the latter was not statistically independent of the former. There was no correlation between per capita fledgling success and duckling mortality on a year-by-year basis, hence the density-dependent pattern in breeding success appears to be mediated through variation in nesting success. The number of paired females at the start of the breeding season correlated positively with the production of fledged juveniles the year before.
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