Project description:Acoustic individuality may well play a big role during the mating season of many birds. Black grouse (Lyrurus tetrix) produces two different long-distance calls during mating on leks: rookooing and hissing calls. The first one represents low frequency series of bubbling sounds and the second one represents hissing sound. This hissing represents a signal not produced by the syrinx. We analyzed 426 hissing calls from 24 individuals in Finland and Scotland. We conducted cross-validated discrimination analyses (DFA). The discrimination model classified each call with almost 78% accuracy (conventional result) and the validated DFA revealed 71% output, that is much higher than classification by chance (4%). The most important variables were Frequency 95%, 1st Quartile Frequency, Aggregate Entropy and Duration 90%. We also tested whether between individual variation is higher than within individual variation using PIC (Potential for individual coding) and we found that all acoustic parameters had PIC > 1. We confirmed that hissing call of black grouse is individually distinct. In comparison to the signals produced by the syrinx, non-vocal sounds have been studied rarely and according to our knowledge, this is the second evidence of vocal individuality in avian hissing sounds which are not produced by syrinx. Individuality in the vocalization of the male black grouse may aid females in mating partner selection, and for males it may enable competitor recognition and assessment. Individually distinct hissing calls could be of possible use to monitor individuals on leks. Such a method could overcome problems during traditional monitoring methods of this species, when one individual can be counted multiple times, because catching and traditional marking is problematic in this species.
Project description:Since 2017, a reinforcement programme was developed to save the last, endangered, Belgian population of black grouse (Lyrurus tetrix), in the High Fens Natural Park. To improve the success of this programme, an analysis of past data of this population was undertaken to understand the causes of its past decline. A time series analysis was applied, using annual spring male census data recorded between 1967 and 2016. In the period 1967-1993, there was a fluctuation around an equilibrium of a population of ca. 40-45 males. The peak of 85 males observed in 1971 was probably due to a succession of several favourable years in terms of environmental conditions, albeit without an exceptional annual growth rate. It seems that fox density, by using the occurrence of rabies as a proxy, has an impact on the black grouse population. After 1993, the population dynamic changed drastically, decreasing continuously until finally reaching quasi-extinction. On average, the population lost 15.4% of its size each year. Climate models, applied in previous studies to explain these population trends in the High Fens, failed to describe this major modification in this population's dynamic and its recent decline. We suggest that this negative effect was mainly induced by a significant increase in predation by red fox (Vulpes vulpes), whose abundance has increased considerably since the 1990s, in particular, as a consequence of the eradication of fox rabies. We also discuss alternative hypotheses, such as the impact of other predator species, modification of the natural environment and climatic modifications.Supplementary informationThe online version contains supplementary material available at 10.1007/s10344-023-01642-w.