PARENTAL CONDITION AND BREEDING EFFORT IN WADERS

1. Body weight of incubating parents, hatching success, parental care during incubation and tending periods after the chicks hatched as well as foraging distances from the nests and chicks were recorded for lap wing (Vanellus vanellus L.), and black-tailed godwit (Limosa limosa L. ) breeding on meadows in Kiskunsag National Park, 50 km south of Budap est (19 degrees 07'E, 47 degrees 08'N). 2. Sex-related differences in parental care were found in both species. Males responded more readily to avian predators and foraged farther from the nests and chicks than did females. In contrast females carried out a greater share of the i ncubation, and played the larger part in caring for the young. 3. Ther e were condition-related differences in parental investment by both sp ecies: heavier females and males incubated for longer than lighter par ents, and males found tending chicks in the late-tending period had be en heavier at the start of the incubation than males that were not pre sent in this period. 4. Weight loss during incubation was recorded onl y in lone females and those laying a replacement clutch when the first had been destroyed. Adverse weather increased the proportion of the f emale time budget spent in incubation and, as a consequence, their bod y weight declined but they were able to regain their former condition, godwits faster than lapwings. 5. The more important role of godwit ma les than lapwing males in care was found. The stronger pair-bond in go dwit than in lapwing was supported by: (i) they have fewer females inc ubating alone; (ii) more godwit pairs tended together in the late-tend ing period; (iii) more godwit females that laid replacement eggs were tending chicks during the late-tending period. 6. The results of this study suggest that reduced parental care may lead incidentally to poly gamy in the lapwing but the greater demands for caring made on black-t ailed godwits act against polygamy developing in this species. The god wit retains monogamy and females benefit by choosing a mate in good co ndition in order to ensure successful rearing of offspring.