Open access publications in the SLU publication database

Abstract

This study is a first attempt to analyze large-scale willow grouse (Lagopus lagopus) population dynamics. In this thesis I studied the population dynamics of willow grouse in the Swedish mountain range. I estimated the scale of synchrony in both breeding success, and the adult segment between populations throughout the mountain range by using time-series of harvest data and population densities estimated from line transect counts. Little evidence of regular fluctuations/cycles in juveniles in autumn was found, and chick production in willow grouse appears to fluctuate more irregularly than was previously believed. Breeding success estimated as number of juveniles per two adults in autumn, showed a spatial correlation between sites up to 200 km apart, but there was no spatial correlation in the adult segment of the populations. When analyzing the presence and strength of time-lags in density dependent processes, a first order process was detected in the southernmost region, and a combination of weak first and second order processes in the northern part of the mountain range. There was a positive relationship between breeding success the previous year and the intrinsic rate of increase in the northernmost region where first and second order density dependence was weak and of equal strength. No such relationship was found in the southern region where density dependence was stronger and dominated by a first order process. Natal dispersal resulted in 80% of the juvenile females dispersing more than 5 km from their summer area, with a mean dispersal distance of 10.2 km, three times further than for juvenile males (3.4 km). Adult females were migratory between wintering areas used as a juvenile and their first breeding site. At landscape scales, only juvenile females and migratory adult females are important in exchange of individuals between populations. Hunters’ effort provided a useful relationship with harvest rate. Setting limits to the totally allowable effort within an area has a stronger potential for controlling harvest than daily bag limits or adjusting the length of the open season. Another simple harvest strategy would be to prohibit harvest in parts of the total area hunted. By setting aside a part of the total area as a buffer, and placing limits on the harvest effort in the open parts of the hunting area, it would be possible to achieve a cost-efficient system with a small risk of over-harvesting.