Weather‐mediated decline in prey delivery rates causes food‐limitation in a top avian predator

Abstract

Inclement weather can negatively affect breeding birds directly by exposure to factors such as severe temperature and rainfall, or indirectly by reducing food supply. During a three‐year study of Arctic peregrine falcons Falco peregrinus tundrius breeding in Nunavut, Canada, we estimated annual prey density at a biologically relevant scale (i.e. the home range of breeding pairs), and examined the manner in which prey density and within‐season weather conditions influenced occupancy of breeding sites, egg‐laying, hatch rate, prey delivery rates and growth and survivability of nestlings. The first two summers of our study (2010–2011) were warm and dry, while the third summer (2012) was cool and wet, and was preceded by a severe spring rain event. We found that occupancy of breeding sites was consistently high. As a proportion of the number of eggs laid, hatch rate did not change among years, but the number of eggs laid per occupied site declined in the third year of the study. In the first two years of the study, the number of nestlings per occupied sited was high, but declined in the third year. Total prey density at the home range scale was similar in 2010 and 2012, while the highest prey density was recorded in 2011. Total prey delivery rates to nestlings and nestling growth rates were significantly lower in 2012, which received more precipitation than 2010 and 2011. Nestling growth rates were similar in 2010 and 2011, but were markedly different in 2012; for both sexes the period of rapid growth was of shorter duration in 2012 and asymptotic weights were lower. This research contributes to the growing body of evidence that indicates severe rain events and ongoing periods of wet weather can reduce reproductive output of Arctic‐breeding raptors regardless of whether it occurs during laying, incubation or brood rearing.