Native ant species Myrmica rubra affects Herring Gull Larus argentatus and Lesser Black-backed Gull L. fuscus chick survival at a North Sea island

Abstract

Trischen island is located in the core area of the Schleswig Holstein Wadden Sea National Park, north of the Elbe estuary, and holds one of the largest colonies of Herring Gull Larus argentatus (1,781 pairs in 2013) and Lesser Black-backed Gull L. fuscus (1,838 pairs in 2013) on the German west coast. Productivity has been monitored for both species since 2010, and was low throughout 2010-13, averaging 0.26 ± 0.12 SD fledged/nest for Herring Gull and 0.32 ± 0.14 SD fledged/nest for Lesser Black-backed Gull. Since 2011 excessive ant activity has been noted at some nest sites, causing distress for freshly hatched chicks. In 2013 a total of 83 gull nests (40 Herring Gull, 33 Lesser Black-backed Gull, 10 unspecified) were monitored at 2-4 day intervals and ant activity was recorded. Ten nest sites with chicks that were obviously suffering from attacks by the European Fire Ant Myrmica rubra were noted; all of these chicks (n = 25) died before the age of 4d (± 2d), reflecting a chick loss of 14.5% within the study colony. At the end of the breeding season, ant densities were compared between these ten nest sites where ant attacks had been observed and ten out of the 15 nests sites where at least one chick lived to fledging age. Results showed a 12-fold higher ant density at nests where ant attacks had been observed and a distinctive ant density pattern within the colony, suggesting that location of nesting sites affected chick survival.