COSTS AND BENEFITS OF INTERSPECIFIC COLONIALITY IN BREEDING WADERS

Nest position, laying and hatching data, agressive interactions betwee n foragers, and causes of hatching failures were recorded in lapwing ( Vanellus vanellus), redshank (Tringa tetanus) and black-tailed godwit (Limosa limosa) breeding on 380 ha of meadows in Kiskunsag National Pa rk, 50 km south of Budapest (47 degrees 08'N; 19 degrees 07'E). Meadow s were flooded artificially every autumn, but no water management or a gricultural activities were carried out during the breeding seasons ov er the 8 year study period, 1988 - 1995. All three species laid clutch es in their preferred nest sites during the early laying period, and t his resulted in the formation of single-species colonies. Preferred ne st sites for lapwings were areas of low vegetation a long way from the water. Godwits preferred high vegetation near the water, whereas reds hanks showed a preference for areas mid way between the two latter. In preferred areas, where single species-colonies developed, the frequen cy of aggressive interactions was higher than in mixed colonies or on solitary nest sites. In mid and late laying periods, pairs nested in n onpreferred sites, presumably due to competition, and this produced mi xed-species colonies or solitary nest sites. Lapwings benefited from r educed effects of predation and flooding by rainfall in three-species colonies, where they attained their highest hatching success. Godwits benefited from nesting with lapwings and achieved their highest hatchi ng success in two-species colonies because they nested further from th e water and lost fewer clutches from flooding than in single-species c olonies. Redshanks suffered nest losses due to attacks of neighbouring lapwings and achieved their highest hatching success in two-species c olonies where they bred with godwits. The conspecific and heterospecif ic interactions produced colonies with various compositions that refle cted the balance of costs and benefits for each species to achieve its highest hatching success.