Understanding the mechanisms by which climate change will affect animal populations is vital for adaptive management. Many studies have described changes in the timing of biological events, which can produce phenological mismatch. Direct effects on prey abundance might also be important, but have rarely been studied. We examine the likely importance of variation in prey abundance in driving the demographics of a European golden plover (Pluvialis apricaria) population at its southern range margin. Previous studies have correlated plover productivity with the abundance of their adult cranefly (Tipulidae) prey, and modelled the phenology of both plover breeding and cranefly emergence in relation to temperature. Our analyses demonstrate that abundance of adult craneflies is correlated with August temperature in the previous year. Correspondingly, changes in the golden plover population are negatively correlated with August temperature 2 years earlier. Predictions of annual productivity, based on temperature-mediated reductions in prey abundance, closely match observed trends. Modelled variation in annual productivity for a future scenario of increasing August temperatures predicts a significant risk of extinction of the golden plover population over the next 100 years, depending upon the magnitude of warming. Direct effects of climate warming upon cranefly populations may therefore cause northward range contractions of golden plovers, as predicted by climate envelope modelling. Craneflies are an important food source for many northern and upland birds, and our results are likely to have wide relevance to these other species. Research into the potential for habitat management to improve the resilience of cranefly populations to high temperature should be an urgent priority.