Flight distance and population trends in European breeding birds

Flight distance reflects the risk that individual animals are willing to take when approached by a potential predator, as shown by a negative relationship between susceptibility to predation and flight distance. Species with long flight distances should more often suffer from disruption of their activities by potential predators, including humans, than species with short distances, resulting in declining reproductive success and hence declining population size of such species if disturbance happens more often. Long flight distances thus suggest that individuals need large amounts of space for their body size, resulting in the prediction that species with long flight distances should have a higher frequency of declining populations than species with short flight distances, when human impact on natural habitats increases. Bird species with long flight distances had declining population trends across Europe in a comparative study of 56 species, even when controlling statistically for other factors associated with population declines, with effect sizes ranging from 0.36 to 0.58 (Pearson's r). These findings suggest that standardized measures of flight distance provide reliable information about the population consequences of risk-taking behavior by individuals and the susceptibility of different species to increased levels of disturbance.