Thorup O. (2026) Shifts in breeding timing of Dunlin Calidris alpina and Northern Lapwing Vanellus vanellus and how goose grazing may affect such changes. ARDEA 114 (1): 1-1

From 1986 to 2024 various aspects of the breeding biology of Dunlin Calidris alpina were studied at the Tipperne nature reserve in western Denmark, alongside monitoring of the breeding performance in Northern Lapwing Vanellus vanellus nests in the same area. Despite increases in March and April mean temperatures over the study period, Dunlins delayed their onset of laying, with the median date shifting later by an average of 0.22 days per year. In contrast, Lapwings advanced their median date by an average 0.20 days per year over the same period. A major change in the timing of laying in Dunlin took place after large-scale intensive grazing by Barnacle Geese Branta leucopsis in April and early May, which started in 2000. Dunlins prefer to construct their nests in tufts 9–12 cm high, most commonly of Festuca rubra and Agrostis stolonifera/capillaris, species that are the preferred forage for Barnacle Geese. Heavy goose grazing very likely suppressed the growth of the nesting habitat to the preferred height for nesting Dunlins. Predation rates on early Dunlin nests increased after the onset of heavy goose grazing, particularly during the initial years (1997–1999) when intensive goose grazing first occurred. This pattern was not observed in Lapwing nests. Dunlin chick survival (estimated by local return rates of ringed chicks as adults) indicated substantially higher survival rates among early hatched chicks compared to those hatching later. Breeding Dunlin numbers declined markedly from around 100 pairs to less than ten pairs during 1986–2024. In contrast, Lapwing numbers remained relatively stable (mostly 120–200 pairs) with higher numbers in periods with extensive predator control and lower numbers in periods with a high predation pressure. The change in grazing regime at Tipperne from 2000 onwards characterized by heavy Barnacle Goose grazing during the Dunlin pre-breeding period may have played a key role in the marked decline of the Dunlin at this site.