Hunter's behavioural responses to changes in bag size and willow grouse density : implications for management and interpretation of harvest data

Abstract

An important aspect of ecological research is to provide guidelines and tools to wildlife managers. The ecological feature of density dependence which shapes population responses to harvest are important for wildlife management, but monitoring practices and exploiter dynamics to the changing resources and management regimes should also be included. Bag records are often collected by wildlife managers as part of their management regime, in which monitoring of the harvest is crucial. However, bag records are also commonly used as an index for population abundance and reproductive success. Bag records are valuable for their accessibility at a low cost and are used by researchers to parameterize harvest models and in studying population dynamics. However, seldom are bag records utilised as an index for abundance and reproduction, properly evaluated against abundance estimates based on count data. Moreover, which factors influence hunters’ effort and success (and hence bag size), are not well explored for many game species. In this thesis I present my aims, by means of long-term monitoring records and more short-term experimental data, are (1) to evaluate bag records of willow grouse (Lagopus lagopus) as indices for willow grouse abundance and breeding success and (2) to provide advancement in understanding of the underlying mechanisms determining the harvest rates; the hunters and their behavioural responses to willow grouse and (3) to derive implications for rational management of willow grouse populations. I found the bag size and harvest rate to be more dependent on hunter effort than on willow grouse density and breeding success. The vulnerability of grouse to harvest was different for young and adult birds; young were most vulnerable. Among adults vulnerability depended on whether they had bred successfully or not; reproductively successful adults were most vulnerable. The sex ratio of the adult grouse in the harvest tended to be male-biased, in accordance with what has been found earlier, and independent of willow grouse density and breeding success. Hunter’s daily bag size was at best weakly density dependent. The number of grouse encounters, which was independent of willow grouse density, and gender of the hunter were the two strongest determinants for daily bag size. Hunters general experience in willow grouse hunting seems highly variable and of great importance for their success in bagging grouse. Still, hunters with several years of local knowledge from the hunting area were equally efficient in bagging grouse as hunters with equal experience, but from other hunting areas. Hunters considered less experienced in grouse hunting managed to increase their Catch Per Unit Effort (CPUE) in an area from one year to the next. Less than one third of the hunters return to the same area from one year to the next and the return rate was dependent of their previous CPUE, contrary to what hunters express is important for their satisfaction. In conclusion, I urge caution in relying on bag size and harvest age ratios as indexes for willow grouse abundance and breeding success. The harvest rate was mostly determined by hunter effort and implies a potential for the regulation of hunter effort to maintain sustainable harvest rates. The finding that hunters appear to be selective towards key demographic components of willow grouse populations, such as adults with high reproductive success, suggests that this aspect of hunters’ behaviour should be taken into account when deciding on sustainable harvest levels for willow grouse populations.