Effects of an extreme weather event on seabird breeding success at a North Sea colony

Quantifying the effects of extreme weather is a critical question in population ecology since climate models predict increased climate variability. Effects will vary among and within species due to exposure or susceptibility, yet few studies have considered these sources of variation simultaneously. We investigated the effects of a summer storm on the breeding success of 4 seabird species at a North Sea colony in relation to aspect, height above sea-level, distance to cliff edge and laying date. The storm lasted 8 h with gusts of \ensuremath>60 m s?1. In exposed plots, razorbills Alca torda had higher failure rates (28.5%) than European shags Phalacrocorax aristotelis (15.1%), black-legged kittiwakes Rissa tridactyla (15.6%) and common guillemots Uria aalge (10.4%). Conversely, failure rates in sheltered plots were negligible (shags 0.0%; kittiwakes 1.9%; no guillemot or razorbill plots in sheltered locations). Guillemots breeding closer to sea-level were more likely to fail, but cliff edge proximity did not affect failure rate. In razorbills, pairs that laid early were more likely to survive the storm. In all species, some failed pairs re-laid, and success of re-lays was lower than that of pairs that survived. Thus, re-laying only provided partial compensation, and, overall, the storm caused a net reduction in annual population production of 4.6, 10.7, 8.9 and 22.8% for shags, kittiwakes, guillemots and razorbills, respectively. Increased storm frequency may therefore have important consequences on seabird populations, but orientation of storms relative to colonies and timing in relation to the breeding season are likely to be critical in determining the overall effect.