Seabird census produces mixed results

The latest seabird census of Britain and Ireland has revealed mixed results. Nearly half of the monitored species were found to be in decline, although some have increased.

Seabirds Count, released as a book by wildlife publishers Lynx Edicions on Thursday [16 November 2023], is the most comprehensive seabird census completed to date, providing population estimates for the 25 regularly breeding species of Britain, Ireland, Isle of Man and the Channel Islands.

The survey took place between 2015 and 2021 and was led by the Joint Nature Conservation Committee (JNCC) with more than 20 steering group partners. The census results show that 11 of the 21 seabird species, where there is confidence in their trends, have declined since the last census in 1998-2002. Five species have remained stable while five have increased, with some of those increases linked to targeted conservation work.

Puffin is declining in Britain, which holds some 8% of the global population (Bethan Clyne).

The remaining four species of the 25 surveyed have up-to-date breeding population estimates, but due to survey method changes and improvements these cannot be confidently compared with previous estimates.

The results also differ significantly by region or country. Seabirds Count shows that Scotland has the greatest number of species in decline (14 out of the 20 where trends are known), but still remains an important stronghold for Britain and Ireland's seabirds with 51% of the total population. 

The results in England are mixed, with eight species increasing, six declining and five stable. Seabirds are doing well in Ireland with 15 species increasing and only two declining. In Wales, 11 species are increasing while six are declining. In Northern Ireland, four species are declining, six are stable and seven are increasing.

The main drivers for declining populations vary between species and even location; however, there are some common themes. Predation is a common problem: eggs, chicks and adults can be eaten by native and invasive predators, which may have been released onto seabird colony islands or, in the case of Brown Rats or American Mink, may have stowed away on boats.

Climate change is another important factor. Increased water temperatures reduce the availability of important food such as sandeels, which leads to seabird parents not finding enough food. This is exacerbated by fish stock depletion by commercial fisheries, meaning there's not enough food to go around during the important breeding season. Additionally, adverse weather conditions have caused nest sites to be swept away and make foraging conditions more difficult.