Weak compensation of harvest despite strong density–dependent growth in willow ptarmigan

Abstract

Ptarmigan and grouse species (Lagopus spp.) are thought to be able to compensate for a modest harvest because there is a surplus of breeding birds that are prevented from breeding by territory holders. To estimate the degree of harvest-mortality compensation reliably we experimentally harvested 0%, 15% and 30% of the willow ptarmigan (Lagopus lagopus) on 13 estates ranging from 20 to 54 km2 in size during four hunting seasons in Norway according to a regional block design. Population overwinter growth rate was strongly negatively density dependent, but despite this, and contrary to earlier findings, only 33% of the harvest was compensated for. The lack of compensation was probably caused by long-distance juvenile dispersal that was unaffected by the harvest. The need for large-scale management experiments to detect the effects of harvest was clearly demonstrated: lack of compensation was found only when we used the whole dataset and not when the data were analysed by year or block. Our study shows that it is very difficult to demonstrate a population's lack of harvest compensation and warns against using small-scale, out-of-season or poorly replicated studies as a basis for future harvest-management decisions.

Demographic transition among hunters: a temporal analysis of hunter recruitment dedication and motives in Denmark

“…Unrestricted harvesting within the seasonal limits has historically been regarded as an activity that only takes out a surplus of the populations (Pedersen et al 2004), despite the fact that scientists provided new knowledge about the eff ects of hunting as early as in the 1990s (Kastdalen 1992, Smith and Willebrand 1999, Willebrand and Hornell 2001. Th e studies show quite clearly that harvesting may add to the natural mortality in willow ptarmigan in contrast to the old view of harvesting from a surplus (Sandercock et al 2011).…”

Grouse Hunting Regulations and Hunter Typologies in Norway

“…Key-words: bag limit, game, harvest, willingness-to-pay, ptarmigan Declining grouse populations is a pressing management issue worldwide (Storch, 2007). The underlying causes are complex, and while no study has yet identified one single factor that explains the declines at larger spatial scales, the most prominent threat seems to be habitat loss, degradation and fragmentation (e.g., Webb, Boarman, & Rotenberry, 2004;Marzluff & Neatherlin, 2006): changes that are long-lasting and not easily reversed.Additionally, we see growing evidence that game-bird hunting may be more additive to other causes of mortality than previously thought (Smith & Willebrand, 1999;Pedersen et al, 2004;Pöysä et al, 2004;Sandercock, Nilsen, Brøseth, & Pedersen, 2011;Connelly, Hagen, & Schroeder, 2011; but see also Sedinger, White, Espinosa, Partee, & Braun, 2010).It thus seems clear that harvest regulations are inevitable for mitigating grouse population declines. Management agencies then face a partly conflicting quest; they must achieve the ecological goal without overly restricting hunting opportunities and thereby jeopardize hunter satisfaction.…”

Large-scale climate variability and rodent abundance modulates recruitment rates in Willow Ptarmigan (Lagopus lagopus)

“…At each encounter, the number of birds (chicks, adult males, adult females and birds of unknown age/sex) and perpendicular distance from the transect line to the observed birds (m) were recorded. Pedersen et al (2004) provide a detailed description of the sampling protocol. The number of years with data in each survey area varied between three and 15 (median = 7); the number of transects per survey area varied between two and 39 (median = 11), giving total transect lengths varying between 7.6 and 107 km (median = 33 km); and the number of encounters per year per survey area varied between four and 179 (median = 30).…”

“…This allowed us to estimate the proportion of juveniles from each encounter for each year in all survey areas and mountain regions separately. Large clusters are easier to detect than small clusters, and dogs spend more time searching close to the transect line than farther away (Pedersen et al 2004). This might result in a size bias where average cluster size becomes larger at long distances compared to distances close to the transect line, and consequently, estimates of cluster size might be overestimated.…”

“…1). Volunteer dog handlers with pointing dogs walked along predetermined transect lines and the free-running dogs searched the area on both sides of the line following the procedure of distance sampling (Buckland et al 2001;Pedersen et al 1999Pedersen et al , 2004Warren and Baines 2011). At each encounter, the number of birds (chicks, adult males, adult females and birds of unknown age/sex) and perpendicular distance from the transect line to the observed birds (m) were recorded.…”