Reproductive Indices of Common Murres Uria aalge and Marbled Murrelets Brachyramphus marmoratus Indicate Murrelets are More Resilient during Poor Years

Fledgling encounter rates at sea were used as measures of annual reproductive performance for Common Murres Uria aalge and Marbled Murrelets Brachyramphus marmoratus over 29 years in two marine biogeographic regions off the coast of Oregon, USA, north and south of Cape Blanco. In both bioregions, the adult murre population was much larger and the encounter rate of murre fledglings was much higher than for murrelets overall, but the apparent decline in productivity during El Niño events and years of poor foraging was significantly greater in murres than in murrelets. We conclude that murrelets are better at coping with variations in food availability as a function of ocean conditions. Different foraging strategies and body sizes may explain the differential success rates during years of low prey availability.