A long-term study of Little Stint in southern Sweden has assessed the overall autumn abundance of the species over a 75-year period.
Worringly, its findings back up other recent research and suggest that the shorebird is in trouble.
Using trapping data collected between 1946 and 2020, Jonas Waldenström and his colleagues analysed the timing and abundance of Little Stint occurrence at Ottenby Bird Observatory during autumn.
Some 4,791 Little Stints were trapped during the study period, but the researchers found that the number of birds appearing annually had significantly declined. More specifically, the number of juveniles dropped from median 31 (mean 74) in 1946-1999 to median 1.5 (mean 3.5) birds in 2000-2020. Closer analysis suggested that the decline in abundance of juveniles started around 1984, while since 1993 the median number never exceeded seven.
The number of juvenile Little Stints being recorded at Ottenby, Sweden, in autumn has declined in recent decades (Mick Kemp).
The number of adult Little Stints recorded throughout the 75-year study period was low and showed no trend in terms of abundance. However, the timing of return migration of adults has become progressively earlier, with their appearance at Ottenby having advanced by 26 days between 1946 and 2020. Meanwhile, juvenile passage advanced by nine days over the same period. Given that spring passage sometimes does not peak until the final week in May, the researchers believe that the big advance seen in the average date of autumn adults hints at an increased proportion of failed breeders.
Overall, the team says that the combination of earlier migration of adults and decreased numbers of juveniles suggests low reproductive output in recent decades.
These findings reflect observations elsewhere. Declines have been reported from the west of the species' breeding range in northern Norway, while numbers on Mauritanian and Namibian wintering grounds are also reported to have decreased. An accelerating decline is described from the East Atlantic Flyway as a whole.
Waldenström and his peers suggest that the reasons for decline likely lie on breeding grounds, citing similar observed decreases in other High Arctic waders, such as Curlew Sandpiper and Ruddy Turnstone. Previous research has linked Curlew Sandpiper breeding success to lemming cycles; when there are more lemmings, Curlew Sandpipers have better breeding seasons due to an abundance of available prey for predators, and vice versa.
The team highlights a number of factors that are likely driving reduced nesting success in High Arctic shorebirds. Their breeding grounds are bearing the brunt of human-induced climate change and increased temperature rises in the Arctic are likely to be causing increased mismatch between arrival of birds and peak food availability, as well as more frequent extreme weather events and higher levels of predation – indeed, in a global dataset, Arctic-breeding waders showed a threefold increase in daily nest predation rate between 1944 and 2016.
Reference
Waldenström, J, van Toor, M, & Lindström, Å. 2023. Long-term trends in abundance, phenology, and morphometrics of Little Stint Calidris minuta during autumn migration in southern Sweden, 1946-2020. Ornis Svecica, 33, 30-48. DOI: https://doi.org/10.34080/os.v33.23489
