Open Access

Joseph Stephan

• This bachelor thesis investigates the factors influencing the breeding success of Little Terns and other shorebirds within predator exclosures at three study sites in the Danish Wadden Sea: Blåvandshuk, Lakolk Strand on Rømø, and Grønningen on Fanø. The research focused on sand drift dynamics, habitat characteristics, decoy effects, predator pressure, and human disturbance. A standardized sampling design was applied at Blåvandshuk and Lakolk Strand to monitor changes in sand drift and surface cover composition. Moreover, environmental parameters and Little Tern responses to 3D-printed decoys were recorded at Blåvandshuk. In addition, nest monitoring at all three study sites provided insights into breeding success and nesting habitat preferences. Predator pressure was assessed by an artificial nest experiment at Blåvandshuk and Lakolk Strand. Finally, surveys of beach visitors and dog counts at Blåvands-huk quantified awareness of the seasonal dog leash law and potential human disturbances. Results showed that both Lakolk Strand and Blåvandshuk were affected by sand drift, with Blåvandshuk more severely exposed due to a higher proportion of bare sand. Little Terns showed a preference for shell-rich, sparsely vegetated backshore areas within predator exclo-sures. The 3D-printed decoys effectively attracted Little Terns, but did not lead to nesting, likely due to more suitable habitat elsewhere. Observations of eight fledged chicks at Grønningen, together with one fledged chick from Juvre Sand on Rømø represented the only breeding suc-cess of Little Terns in the Danish Wadden Sea in 2025, marking the least successful breeding season on record. Artificial nest experiments revealed high predation rates at Blåvandshuk, mainly by red foxes and corvids. Predation rates were much lower at Lakolk Strand, highlight-ing the effectiveness of ongoing predator control on Rømø. Human disturbance, especially from off-leash dogs, remains a major threat to resting and breeding shorebirds at Blåvandshuk. Altogether, the study demonstrates that safeguarding Little Terns and other coastal breeding birds within predator exclosures depends on coordinated habitat management, predator con-trol, and regulation of human activities.