A team led by Martin Beal of BirdLife International has investigated whether it is more important to spread GPS tracking effort of seabirds across multiple years or to tag more individuals when identifying important areas for marine conservation.
Tracking data is a well-established part of the conservation toolkit for seabirds, allowing important feeding areas to be identified and for the impacts of commercial fishing and other threats to be better understood. The importance of tracking a large enough sample of the population has been a hot topic in the research community in recent decades, as has the potential of a population to use different areas from year to year and the implications for mapping distributions. However, which approach should take priority in this costly field of research has not been properly investigated until now.
The data review included tracking studies of 23 seabird species, including Cape Verde Shearwater (Rob Williams).
Global standards are in place for identifying important sites for biodiversity, including accounting for annual variation in distribution by setting a minimum threshold for the number of years over which a population is studied and mapped. One of the questions the new research sought to answer was whether this is truly necessary or appropriate in all species and situations, given the effort and expense involved in tracking in remote locations over long periods of time.
The researchers assessed tracking data from the chick-rearing period for 23 species from seven of the 14 seabird families to assess whether the focus should be on studying a certain proportion of the population or spreading the effort across years. The chick-rearing period is important as this is when the movements of seabirds are most restricted and when conservation management of important areas has the most potential to recover or protect seabird colonies.
The variation in distribution between years for each species included in the research was studied and viewed against the taxonomy, habitat and latitude of each species to see whether patterns emerged.
Tracking study datasets were resampled by the team to test both the influence of the number of individuals tracked as part of a study and the importance of tracking over multiple years in an effort to inform how resources should be focussed in future tracking projects.
It was found that there was little variation in distribution during the chick-rearing period between years across a wide variety of the seabird species included in the research. This meant that, although tracking birds over multiple years did improve estimates of population-level distributions, the effect was small. Overall, one year of tracking would miss just 5% of the distribution generated by tracking the same number of individuals over the course of three years.
On the other hand, ensuring the sample of tracked individuals is representative of the population being studied was shown to crucial when it comes to using tracking data to identify areas for conservation management.
Given the marginal benefits of multiple-year studies, the researchers suggested that tracking a representative sample of the population over just one or two years will be suitable for assessing distribution in order to identify key areas and implement conservation action.
It was concluded that ensuring enough individuals are tracked is the key consideration in providing a representative estimate of a population's distribution, and therefore identifying key areas for conservation, rather than focussing on tracking over multiple years.
The researchers said that analysing tracking data during the pre-laying, incubation and non-breeding periods would further improve understanding of annual variation in distribution, as movements are less constrained during these phases. In addition, they pointed out that the lack of tracking studies for small-bodied and tropical seabirds prevented wider conclusions from being made. However, the work does have significant implications for the application of tracking data and the planning of future seabird conservation projects.
Beal, M, Catry, P, et al. 2023 Quantifying annual spatial consistency in chick-rearing seabirds to inform important site identification. Biological Conservation 281: 109994. DOI: https://doi.org/10.1016/j.biocon.2023.109994