Population trends of the Peregrine Falcon in Switzerland with special reference to the period 2005–2016

We study population trends of the Peregrine Falcon (Falco peregrinus) in Switzerland with special reference to the development since 2005 and three study areas, South West Switzerland (4,993 km², 1960–2015), the Northern Jura mountains (3,270 km², 2005–2015) and the Canton of Zurich (1,748 km², 2002–2015). We used dynamic occupancy models, which allow the territory-specific extinction and colonization parameters – the demographic rates (at the territory level) underlying a population trend – to be estimated. The Swiss peregrine population has developed in line with trends observed in many other countries and regions in North America and Europe: after the pesticide-induced collapse between the 1950s and 1970s, the population largely recovered up to the turn of the millennium. However, in recent years, we detected significant declines again: in SW Switzerland, the population decreased from 51 to 33 pairs during 2008–2015 (-35%), in the N Jura from 70 to 40 pairs during 2009–2015 (-43%) and in Zurich from 6–7 to 2–4 pairs during 2010–2015 (-50%). In the same time, the local extinction rate in the three study areas (more than) doubled from (0.05) 0.1 to 0.2, while the colonization rate dropped from 0.3 to 0.1 in one of the areas, while no change was detectable in the other two. We discuss two factors responsible for these strong, recent declines of Swiss peregrines: (1) predation by Eagle Owls (Bubo bubo) and (2) direct and illegal persecution by humans. In addition to these two factors, growing human disturbance (e.g. through climbers, bird photographers, paragliders, hikers, geocachers, etc.) and fatalities due to collisions with man-made structures (power lines, glass, wind turbines, etc.) are also suspected to contribute to the population decline.