Annual variation in harvested animals (hereafter bag size) is often used as an index of population abundance when investigating population dynamics. Few studies have evaluated how well bag size tracks population change despite its widespread use. Two recent studies on grouse harvest statistics have reached contrasting conclusions. Th ere is limited information about the functional response of hunters in relation to varying game densities, and effort is seldom recorded. We investigated how much of the variation in bag size (total number of harvested grouse km−2) is explained by variation in willow grouse Lagopus lagopus density (adult and young grouse km−2) and hunting eff ort (total number of hunting days km−2). We also evaluated catch per unit effort (CPUE) as an index of grouse abundance, and estimated the response in harvest rate (total bag size in relation to total grouse density) to varying hunting effort. We used data from the 88 management areas on state land in Jämtland county, Sweden (1996–2007), where hunting days and bag size are recorded in detail. Willow grouse density was estimated in four of these management areas in August using line transects and distance sampling. The hunting effort and total grouse density explained most of the variation in bag size (R2= 0.89). Bag size was twice as sensitive to changes in hunting effort compared to changes in grouse density. More than a ten times change in the grouse population density was required to one unit change in bag size. The use of CPUE did not provide a better alternative index of grouse density, and variation in density only explained 23% of the variation in CPUE. Harvest rate showed a strong relationship with hunting effort, and we suggest that an upper limit in hunting effort can be used to reduce the risk of high harvest rates. Hunters became more efficient at low densities and controlling hunting effort is most important when there are indications of population lows and/or poor breeding. CPUE may be less sensitive to changes in game abundance than previously assumed, and bag size as a proxy for population density would then depend on the ability of hunters to adjust their effort according to population change. We speculate that this ability will depend on whether or not hunters have long‐term experience of a hunting area where they can return to hunt throughout the hunting season. We propose that recording hunting eff ort should be encouraged and possible correlations with game abundance and other factors such as weather should be investigated for game species.
Age and sex ratios in bag records are frequently used as indices of population 18 composition for harvested populations. However, vulnerability to harvest may differ by age 19 and sex thereby producing bias in population estimates. We assessed whether age and sex 20 affected vulnerability to harvest for willow grouse (Lagopus lagopus) where adult density and 21 brood size was known in the harvested populations. We collected bag records during 2 days 22 of controlled hunting in 4 areas in 2 years (2007 and 2008) in Jämtland county, Sweden. We 23 found that vulnerability to harvest was different for chicks and adults, but not between male 24 and female adults. Hunters encountered broods at a higher rate than single birds compared to 25 personnel conducting pre-harvest counts along line transects. Furthermore, the probability of 26 shooting a grouse was higher in encounters of broods than individual grouse. Proportionally, 27we calculated about a 50% probability of a hunter shooting either a chick or an adult 28 1 E-mail: lasse.asmyhr@hihm.no 2 | Asmyhr et al.independent of encountering a single bird or broods of 2-10 grouse. Increasing adult density 29 also increased the vulnerability to harvest for adults relative to chicks, independent of the 30 chick to adult ratio in the pre-harvest population. The different vulnerability of adults and 31 chicks to harvest observed in this study will dampen variation in age classes in bag records 32 compared to the population, and we caution against extrapolation of age ratios in bag records 33 to harvested populations. 34 KEY WORDS age ratio, bag limit, harvest vulnerability, hunters, Lagopus lagopus, selective 35 harvest, sex ratio, willow grouse. 36
Hunters that have options to hunt in different areas should evaluate their previous hunting success when they decide where to hunt. Following optimal foraging theory for nonhuman predators we investigated if hunting success and density of other hunters on the hunting area will affect the probability of return to the same area, and if such behavioural changes will result in a higher hunting success compared to hunters that change to a new area.For this purpose we used detailed information about willow grouse (Lagopus lagopus) hunters on state owned land in Sweden. We found support for the optimal foraging theory application on grouse hunters' behavioural changes according to hunting success. The return rate increased with increasing hunting success and hunters that returned to the same area also increased their success compared to hunters that changed to a new area. Only one third of the hunters returned to the same area the subsequent year. We also found a negative effect of density of hunters in an area on hunters return rates and their hunting success, suggesting crowding among Swedish grouse hunters.
Context. Nest predation is a major factor influencing life history and population dynamics of ground-nesting birds. The transitions between the northern boreal mountain birch forests and the low-alpine tundra are important habitats for the willow ptarmigan, Lagopus lagopus (Linnaeus, 1758). During the past decades, these landscapes have been extensively developed with cabin resorts in southern Norway, which has led to an increased number of roads and foot paths in relatively undisturbed habitats. Aims. The aim of the present study was to investigate relative nest-predation rates in elevation gradients (ecotones) spanning from northern boreal mountain birch forests to low-alpine tundra in three locations with contrasting willow ptarmigan densities. Methods. We conducted an artificial nest study by using baited track boards (n = 108). Track boards were placed along transects (200 m) in the following three habitat types: birch forest, edge habitat and low-alpine tundra. Predator prevalence was analysed in relation to studydesign variables (location, habitat, study period) and the load of human infrastructure (i.e. distance to foot paths and roads), using generalised linear mixed-effect models assuming binomial distribution for the response variable. Key results. Prevalence of avian predators was consistently high (range 38.2-85.3%), in contrast to much lower prevalence of mammalian predators (range 2.8-22.9%). Raven (Corvus corax) was the dominant nest predator, followed by hooded crow (C. cornix) and pine marten (Martes martes). Location, as contrasted by differences in willow ptarmigan density, was not significantly related to total relative predation rates. Species-specific predator prevalence was habitat specific and related to human infrastructure, but with opposite relative predation patterns between pine marten and raven. Hooded crow predation was similar across the ecotone and not related to human infrastructure. Conclusions. Predator prevalence was habitat specific and affected by human infrastructure (distance to human foot paths). Our study confirmed that human activity might alter the predation rates by generalist species in these low-alpine environments. Implications. We recommend that attractive willow ptarmigan habitat should be avoided when planning human infrastructure in alpine ecosystems. To reduce predation pressure in this ecosystem, it appears that generalist predators should be considered for management actions. Further research is needed to explain the underlying mechanism driving expansion of generalist species into alpine habitats. Such knowledge is also important in developing alternative management actions with focus other than predator control.
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