Survival and population viability analyses of the declining Black-headed gull in the inner Oslo fjord | Survival and population viability analyses of the declining Black-headed gull in the inner Oslo fjord

Statistical models and models for population dynamics are crucial for understanding and projecting the effects of influential factors on ecosystems and their populations. This understanding can help us implement efficient conservation actions for endangered species. Seabird populations are declining worldwide, and the Black-headed gull was recently listed as critically endangered on the Norwegian Red List. The inner Oslo fjord is one of two main areas for the Norwegian population. The reasons behind the current population decline are unclear. I used capture-mark-recapture data of 2700 ringed Black-headed gulls to estimate the survival of the population living in the inner Oslo fjord. The first-year survival rate was notably low at 0.358 (and 0.0474 with additional data). Second-year survival was 0.795, and 0.850 for individuals aged 2 or older. Survival differed between colony locations. This thesis also provides a matrix population model for the current Black-headed gull population living in the area. The long-term population growth rate was 0.906. The decline in the population studied was due to high first-year mortality. One way to ensure a stable population growth rate is either to increase chick survival from 0.133 to 0.438, or the entire first-year survival must increase from 0.0474 to 0.154. Adult survival was highly sensitive to stochastic environments, and even a small decrease in annual adult survival can have large effects on the survival of the whole population. Management must prioritize increasing first-year survival by protecting colonies during the breeding season and ensuring a healthy Oslo fjord to prevent local extinction.