The roles of climate and alternative prey in explaining 142 years of declining willow ptarmigan hunting yield

Long time series are important because they extend back to an era when animal populations were less influenced by habitat loss and climate change. Annual fluctuations in harvest yields are good proxies for large changes in population size and may reveal underlying ecological processes. From a variety of sources, we built a 142-year long time series representing the mean daily catch (CPUE) of willow ptarmigan Lagopus lagopus in southeastern Norway. CPUE decreased over the 142 years, from 35 birds shot per day in early years to around two in the last years. There were three periods in the time series: a first period with 3-5 year cycles of high peaks and low troughs (1872-1900), a short second period with similarly high peaks, variable depth of troughs and variable cyclicity (1901-1916), and a third long period with much lower peaks and faded cycles (1917-2013). Yearly variation in CPUE was best explained by an interacting effect of small rodent peak years and period, with a reduced posit...