Gyrfalcon and Rock Ptarmigan: a study on predator prey relationship

A population model for the Icelandic rock ptarmigan has been made based on data collected in North-east Iceland since 1981. The model can simulate the 10 year cycle of the ptarmigan and indicates that autumn and winter mortality rates of first year birds are the demographic explanation of the cycle. This mortality rate, termed excess juvenile mortality , changes in delayed density dependent mode peaking two to four years after the peak in ptarmigan numbers. There is a significant relationship between gyrfalcon population size and ptarmigan juvenile excess mortality suggesting that gyrfalcon predation could be one of the factors driving the ptarmigan cycle. The lecture will be about the studies that the model is based on, i.e. the study area and how these studies have been conducted. Also, what these studies have shown about the life histories of these two species and their relationship. Special emphasis will be on the functional response and the numerical response of the gyrfalcon population in relation to changes in ptarmigan numbers.