Demographic data on avian species are critically important for conservation and management. Research on avian demography often requires some level of human disturbance at nest sites. We document researcher disturbance influence on Double-crested Cormorant (Nannopterum auritum: cormorant) reproductive parameters of nest success and survival at breeding colonies on Spider and Pilot Islands, Lake Michigan, Wisconsin, USA. Cormorant nests were monitored daily throughout the breeding season (April–August) via game cameras. Breeding colonies were subject to research disturbance of band resighting efforts, adult capture, and fledgling banding. Over two field seasons, we reviewed 399,674 photographs from 32 game cameras, with 187 nests used in analyses. Nests were 16.82 times more likely to fail on days researchers visited the island compared to days they did not. Nests in 2011 were 6.16 times more likely to succeed than nests in 2010. Nests were 1.76 times more likely to succeed during the chick stage than the egg stage. Nest survival for both islands increased substantially from 2010 to 2011 averaging 50.0% and 89.1%, respectively. Nest survival over the years and islands with researcher disturbance excluded from analyses averaged 75.15% (52.3%–97.7%), compared to 69.58% (40.9%–91.8%) with researcher disturbance. Researcher disturbance had a substantial impact on cormorant nest success in 2010. When researcher visits in 2011 were limited to the chick rearing period, nest failures declined markedly on both islands, but research disturbance still had a negative effect. Our research suggests the literature on cormorant demography may underestimate nest success and survival. We recommend researchers conduct surveys after hatching and take precautions to limit disturbance, such as after dark entry and exit from colonies and use of blinds and technology (cameras, drones) where feasible and applicable.
Dorr et al. (Thu,) studied this question.