Surveys of the largest Leach's Storm Petrel colonies in the north-east Atlantic have found them to be in rapid decline.
The findings mirror trends observed elsewhere in the species' range. The biggest Leach's Storm Petrel colonies are in Newfoundland, Canada, where huge population declines have occurred – the largest colony declined by 42% over 29 years, equating to the loss of more than a million breeding pairs.
To investigate how the species was faring in the north-east Atlantic, fieldwork was carried out in June 2018 on the island of Elliðaey, in Iceland's Vestmannaeyar archipelago, and then on St Kilda, Outer Hebrides, in June-July 2019. The latter had not been surveyed fully for the species since the summers of 1999 and 2000.
Leach's Storm Petrel populations are decreasing rapidly in many parts of its range (Joe Pender).
Active Leach's Storm Petrel nests were counted by using playback at the entrance to burrows. If occupied, adults will generally respond by calling back to the recording, allowing scientists to formulate a good estimate of how many pairs are nesting.
The findings, which were recently published in The Seabird Group's journal, Seabird, paint a worrying picture. Elliðaey's population of Leach's Storm Petrel was estimated to stand at around 5,400 pairs, having declined by almost a third (29%) in 26 years. Alarmingly, the decline on St Kilda was even more severe, with a more than two-thirds drop (68%) in numbers in just two decades to a current population of 8,900 pairs.
St Kilda previously held almost all (94%) of Britain and Ireland's breeding Leach's Storm Petrels and the observed decline led to the species being classified as Critically Endangered in the UK in the recent Birds of Conservation Concern report.
Reasons for the rapid declines are not known, but the researchers suspect multiple factors are involved. Work is underway to track the movements of Leach's Storm Petrels at sea, with a project to tag the species that started in 2021 set to continue this summer. The hope is that they will provide enough data to inform conservation efforts and marine management decisions that could impact the species.
Deakin, Z, & 29 others. 2021. Decline of Leach's Storm Petrels Hydrobates leucorhous at the largest colonies in the northeast Atlantic. Seabird 33: 74-106.