Chick survival and hunting are important drivers for the dynamics of two Alpine black grouse Lyrurus tetrix populations

Niklaus Zbinden,Michael Schaub,Radames Bionda,Luca Rotelli

doi:10.2981/wlb.00874

Abstract

Alpine black grouse populations are generally declining, but the underlying demographic drivers are largely unknown. We studied the dynamics of two adjacent black grouse populations over a 20 years period in the Italian Alps that differ in hunting pressure to identify the main demographic process affecting these populations and to study the impact of hunting on males. We collected radio-tracking data and conducted population surveys in spring to count displaying cocks and in late summer to determine the breeding success by means of pointing dogs. These different data sets were jointly analysed using a seasonal integrated population model to estimate population sizes and various demographic rates. The two populations fluctuated in size and the number of males from one population increased after hunting intensity was reduced. The main demographic rates did not differ between the populations. Adult survival was relatively low and productivity was high, so the life history shows the feature of a fast turnover species. In both populations, the variability of survival from hatching to the age of five weeks (chick survival) contributed more to the variation of the population growth rates than the variability of survival in later life-history stages, and the former was positively affected by ambient temperatures in July, favouring chick survival. The adult sex ratio of the population where males hunting occurred was shifted towards females, but it evened over time with the reduction of hunting pressure. The adult sex ratio in the population without hunting and the chick sex ratios in both populations were even, suggesting that hunting acted as a mostly additive source of mortality.

Highlights

Black grouse Lyrurus tetrix populations in western and central Europe have been declining during the 20th century and since the 1970s (Bergmann and Klaus 1994, Storch 2000)
Since the populations were surveyed in spring and in late summer, we have developed a seasonal model that describes the dynamics from 15 May to 31 August in year t and the dynamics from 31 August in year t to 15 May in year t + 1
The output of the integrated population model (IPM) is rich with many parameters, and in the following, we present the biologically relevant ones

Summary

Introduction

Black grouse Lyrurus tetrix populations in western and central Europe have been declining during the 20th century and since the 1970s (Bergmann and Klaus 1994, Storch 2000). The interplay between demography and resulting population dynamics has, only rarely been investigated In these studies, the variation of productivity has been identified to be the principal process inducing variation in population size (Baines et al 2007, Jahren et al 2016). We monitored black grouse populations both in spring by counting displaying males and in late summer by means of pointing dogs in order to determine the breeding success. The former survey has the disadvantage that it includes the males only, while the latter method typically does not include all individuals due to imperfect detection and incomplete coverage. We estimate age- and sex-specific seasonal survival probabilities, different components of productivity and age- and sex-structured population sizes

Objectives

Methods

Results

Discussion

Conclusion