No abstract

Declines in populations of capercaillie (Tetrao urogallus) and black grouse (Lyrurus tetrix) have been reported from both Central Europe and the continuous boreal forests of Fennoscandia. While intensified land-use is assumed to be the underlying cause of these declines, the mechanisms are not yet understood. Predation is the proximate cause of mortality of eggs, chicks and adults throughout capercaillie and black grouse ranges, but the link between predation and habitat and/or climate change remains unclear. To investigate temporal trends in reproductive output of woodland grouse, we collated previously published and unpublished data of reproduction in capercaillie and black grouse throughout their ranges from 1930 to 2012. We show that, overall, reproductive success has decreased and stabilized at low levels in most regions whilst capercaillie reproductive output in Scotland is still declining. With today's net reproduction, capercaillie and black grouse adult survival is too low to compensate for reproduction declines. Consequently, populations are expected to further decline unless reproductive performances improve. We put our findings in the context of changes in land use, climate and generalist predator numbers. By critically reviewing how these factors limit reproductive success in capercaillie and black grouse, we hope to shed light on the underlying mechanisms causing the decline. Our results imply that measures should be undertaken to reduce mortality of capercaillie and black grouse chicks and eggs. We suggest that future studies should aim to better understand which predators limit capercaillie and black grouse populations and how predation rates are mediated by continuously changing habitat and climate.

We studied depredation rates on free-ranging domestic sheep (Ovis aries) by Eurasian lynx (Lynx lynx) in 2 areas in Norway to test whether selected individuals or a demographic group within a lynx population kill a disproportionate share of livestock. During 6 grazing seasons from 1994 to 1999 , we monitored 34 radiocollared lynx during 641tracking periods (either all night or during a full 24-hr period). Sixty-three domestic sheep and 3 domestic goats were killed by radiocollared lynx during these periods. All of the radiocollared lynx had access to free-ranging domestic sheep within their annual home ranges. Male lynx killed sheep more frequently than females and were responsible for 12 out of 13 cases of surplus killing. After adjusting for number of nights monitored, sheep-killing rates among males differed slightly, whereas the differences between individual females were correlated with the number of sheep available. There were no indications of any special "problem individuals," but rather a "problem sex." Therefore, it seems to be intrinsic in their behavior that males are likely to kill domestic animals more frequently than females. The lack of specific problem individuals in this study might depend on the livestock-herding technique used in Norway, where sheep generally are free-ranging and unattended throughout a lynx's home range. Selective removal of depredating males requires that the gap in the social mosaic either remains unfilled or is filled by an individual that causes less damage to livestock. The effects of such removal on sheep depredation are likely to be only temporary since all adult and yearling male lynx appear to kill sheep.

BackgroundHuman food subsidies can provide predictable food sources in large quantities for wildlife species worldwide. In the boreal forest of Fennoscandia, gut piles from moose (Alces alces) harvest provide a potentially important food source for a range of opportunistically scavenging predators. Increased populations of predators can negatively affect threatened or important game species. As a response to this, restrictions on field dressing of moose are under consideration in parts of Norway. However, there is a lack of research to how this resource is utilized. In this study, we used camera-trap data from 50 gut piles during 1043 monitoring days. We estimated depletion of gut piles separately for parts with high and low energy content, and used these results to scale up gut pile density in the study area. We identified scavenger species and analyzed the influences of gut pile quality and density on scavenging behavior of mammals and corvids (family Corvidae).ResultsMain scavengers were corvids and red fox (Vulpes vulpes). Parts with high energy content were rapidly consumed, mainly by corvids that were present at all gut piles shortly after the remains were left at the kill site. Corvid presence declined with days since harvest, reflecting reduction in gut pile quality over time independent of gut pile density. Mammals arrived 7–8 days later at the gut piles than corvids, and their presence depended only on gut pile density with a peak at intermediate densities. The decline at high gut pile densities suggest a saturation effect, which could explain accumulation of gut pile parts with low energy content.ConclusionsThis study shows that remains from moose harvest can potentially be an important food resource for scavengers, as it was utilized to a high degree by many species. This study gives novel insight into how energy content and density of resources affect scavenging patterns among functional groups of scavengers.

Eurasian lynx (Lynx lynx) are responsible for significant depredation on domestic lambs in Norway. Recreational hunting of lynx is widely used to limit lynx population growth and to attempt to remove problem individuals. We analyzed the relationship between annual changes in lamb losses and lynx hunting on 2 scales. On the county scale, lamb losses were related to the size of the lynx population that was reduced through the harvest of 294 lynx by hunters during our study, 1995–2001. At the level of individual grazing areas, we documented a significant local effect of lynx harvest (n = 321 lynx); however, the magnitude of this benefit was so small (13 lambs per male lynx, or 2 lambs per female lynx) as to be of little practical benefit. The data indicate that lynx hunting only reduces depredation when it reduces the size of the population.