Striking centennial-scale changes in the population size of a threatened seabird

Many animal populations are under stress and declining. For numerous
marine bird species, only recent or sparse monitoring data are available,
lacking the appropriate temporal perspective needed to consider natural,
long-term population dynamics when developing conservation strategies.
Here we use a combination of established paleoenvironmental approaches to
examine the millennial-scale dynamics of the world’s largest colony
(representing ~50% of the global population) of the declining and
vulnerable Leach’s Storm-petrel (Hydrobates leucorhous). By reconstructing
the last ~1,700 years of the colony’s population trends, we corroborate
recent surveys indicating rapid declines since the 1980s. More
surprisingly, however, was that population size was smaller and has
changed strikingly in the past, even prior to the introduction of human
stressors. Our results challenge notions that very large colonies are
generally stable in the absence of anthropogenic pressures and speak to an
increasingly pressing need to better understand inter-colony movement and
recruitment when inferring range- and species-wide trends. While the
recently documented decline in storm-petrels clearly warrants conservation
concern, we show that colony size was consistently much lower in the past
and changed markedly in the absence of major anthropogenic activity. In
response, we emphasize the need for enlarged protected area networks to
maintain natural population cycles, coupled with continued research to
identify the driver(s) of the current global seabird decline.