Data from: Top-down control of a marine mesopredator: Increase in native white-tailed eagles accelerates the extinction of an endangered seabird population

1. Bottom-up control is an important regulator of marine mesopredators
such as seabirds. The prevalence of top-down control on these species is
however less well understood. In particular, how native predators affect
seabird populations has rarely been quantified. 2. Here, we investigate
how an increase in white-tailed eagles in northern Norway, a stronghold
for the species, affected a local population of 25,000 pairs of
black-legged kittiwakes, a red-listed seabird, during a 42-year period
ending with colony extinction. We use a natural experiment of two
neighbouring colonies with/without eagle predation to disentangle the
effects of eagles from local kittiwake foraging conditions (using size of
young herring as a proxy). 3. At the colony where eagle predation
occurred, and in contrast to the eagle-free colony, kittiwake breeding
success and population size declined with increased eagle abundance, the
latter more strongly under poor foraging conditions. Breeding success
increased with foraging conditions at both colonies. 4. Simple population
modelling shows that although conditions were insufficient to sustain the
eagle-exposed colony, the increased abundance of eagles sped up its
extirpation by many years. 5. Policy implications. Our study shows that
top-down effects from avian predators can be significant regulators of
seabird populations, challenging their conservation where native, often
protected, predators are rising. Such effects, and their possible
interaction with other factors, must also be accounted for when using
seabird demographic traits as environmental indicators and when developing
more flexible and effective management and action plans.