Using population modelling to understand the dynamics of the Sussex peregrine falcon (Falco peregrinus) population

The peregrine falcon, Falco peregrinus, is a charismatic bird of prey, which belongs to the Family Falconidae. It was once listed as an endangered species, but through dedicated conservation efforts it is now of least concern. The peregrine falcon is the perfect case study for measuring the impact of conservation efforts on species on the brink of extinction, with just 360 pairs remaining in 1963, which have since recovered to 1750 thanks to the conservation efforts taken. The focus of this study was on the peregrine falcon population of Sussex, in which the data was provided by the Sussex Peregrine Study (SPS) who have one of the most comprehensive historical records of peregrine falcons. Using the data provided, Geographical Information Systems (GIS) and Population Viability Analysis (PVA), many different population elements were analysed in a historical context, such as the density and location of peregrines, the productivity of the population and the probability of survival of populations at different time points. Using the more recent records, the recolonising population was explored and compared to the historical records. As this population is a new inhabitance of the county of Sussex, the peregrines nesting preferences were also analysed, indicating factor preferences such as location and nest type. As the modern population has exceeded historical records, nests have been established further north than previously witnessed. Records show a pattern of high egg and young productivity in the early 1900s (and before World War 2) and 1990-2016, with 1941-1988 having minimal productivity, showing the direct relationship between the successful production of young, the stability of a population and anthropogenic pressures. The early low productivity and relatively small number of birds in the early 1900s were caused by egg collection and persecution, while the later lack of productivity and final disappearance of peregrine falcons were due to organochlorine pesticide poisoning. From the different nest types being established, an order of preference has been established which is coastal, inland and manufactured from most to least favoured. An analysis of the records indicate that this is also the order of most to least productive nest type. The PVA based on current (optimal) parameters indicated that the stable pre-crash population could have continued to grow under these conditions; however, the 1941 population was already too diminished to survive even in the optimal conditions. The 0-productivity simulation indicated that all populations would go extinct, as no offspring would be created to continue the population. The persecution model indicated that more robust stable populations could survive these conditions; however, persecution had a greater effect than lack of productivity on smaller populations. The model which mimics the conditions witnessed in the population crash of the peregrine falcon shows that no population, no matter how robust, would survive under these circumstances. In conclusion, the indirect conservation efforts taken in the UK to protect the peregrine falcon population were incredibly successful as they tackled the primary issue of productivity, while reducing the lesser impact of persecution which is detrimental for smaller populations. Lessons can be learnt from this study and applied to other raptors facing population declines or slow recovery rates.