Summary

The critically endangered hooded grebe Podiceps gallardoi has suffered a population reduction of 80% in the last 25 years. Although climatic conditions are suggested to be important causes of this decline, invasive species are also having a large impact. Hooded grebes have the lowest recruitment rate within the Podicepodiformes, but this is usually compensated by high adult survival. Considering these life history traits and threats, we designed the ‘colony guardian programme’, which aimed to protect nesting grebes by reducing the negative impacts of American mink and kelp gull on breeding colonies of grebes in central-western Santa Cruz Province, Argentina. Over five breeding seasons between 2011 and 2015, 10 colonies were protected using a total of 755 fieldwork days. Colonies guarded throughout the breeding season had higher recruitment (0.64 juveniles/breeding pair) than colonies with little or no protection (0.39 juveniles/breeding pair).