MORE IS NOT ALWAYS BETTER - MALE INCUBATION IN 2 ACROCEPHALUS WARBLERS

This study investigates male and female incubation ability in two mono gamous Acrocephalus warblers with overlapping, equally sized territori es and similar prey abundance. Given the longer breeding time window o f the moustached warbler A. melanopogon compared with the reed warbler (A. scirpaceus), the trade-off between the need for biparental care a nd the cost of inefficient incubation is discussed. Hourly protocols a nd egg temperature measurements were analyzed with regard to four prim ary questions: male and female incubation ability, the role of environ mental parameters, hatching success and the influence of male incubati on on Female time allocation. In both species, males increase egg temp erature per minute at a slower rate than do females. There is no speci es difference ill the percentage of incubation per hour for males (20% ) or females (50%). Ambient temperature influences male incubation onl y in the moustached warbler during the early season April when male in cubation correlates with hatching success. The male reed warbler shows daily temporal selectivity throughout the breeding season, increased incubation during rainfall, and no correlation with hatching success. In both species, females receive direct benefits of increased foraging time through male incubation. However, only the female reed warbler a djusts her incubation duration to previous male incubation. Thus; Fema le reed warblers maximise the male component and thereby reduce the to tal incubation phase with high male effort whereas the incubation phas e is increased with above average male effort in-the moustached warble r.