Possible causes for breading failure in common terns
Mogelijke oorzaken van slecht broedsucces in de visdiefkolonie bij terneuzen. Stand van zaken en aanbevelingen - 2003
Context of the study
Since 1997 the Dutch Coastal and Marine institute (RIKZ) monitors the coastal breading birds of the Delta area. One of these breading birds is the common tern. In 1994 the colony in Terneuzen was struck by serious signs of illness, while the other colonies in the delta area remained healthy. The number of breading couples decreased strongly, and the broedsucces vertaling!!!! was terrible: eggs didn't hatch, young birds were diseased and suffered mass casualties. In 1999 the signs of illness vanished and the number of breading couples increased again. However, after 2000, the eggs started to show anomalies (small cracks or bulges), which indicated that the population still hadn't recovered.
Content of the study
This study investigated possible causes (both ecological as chemical) for the problems in the common tern colony of Terneuzen.
Main results
3 hypothetic causes: infection, toxic plants and chemicals. The first 2 have been eliminated as possibilities. 2 groups of chemicals have been encountered in increased concentrations (higher than in other common tern colonies) Could have been caused by: organotin compounds, vlamvertragers, "unidentified substances"
