Nesting success and status of the least tern breeding colony at Gibson Lake in southwestern Indiana

Federally-endangered interior least terns (Sterna antillarum) have nested at Gibson Lake in southwestern Indiana since 1986. In 2003 and 2004 we evaluated nesting success of least terns and identified factors influencing their productivity at Gibson Lake. In 2003 least terns nested only at secondary breeding sites, composed of deposited ash byproducts from coal combustion. Least terns produced eight fledglings from 39 total nests in 2003; we attributed most nest failures that year to flooding during heavy rains. In 2004 the terns returned to breed at their historical primary breeding site, a narrow gravel dike that bisects Gibson Lake (center dike). However, nesting success again was low in 2004 (13 fledglings produced from 84 total nests), although we attributed most nest failures in 2004 to predation on eggs and chicks by ring-billed gulls (Larus delawarensis). Our study implicated ring-billed gulls as the chief source of mortality on least tern eggs and chicks. The future success of the least tern breeding colony at Gibson Lake ultimately may depend on the establishment and sustained management of alternate breeding areas in the Gibson Lake vicinity.