Breeding Biology of Two Sympatric Coots with Contrasting Conservation Status

Capsule Red-knobbed Coots Fulica cristata and Common Coots Fulica atra have similar breeding biology except in chick survival, which was significantly lower in Red-knobbed Coots.Aims To provide information on the breeding biology of Red-knobbed Coots in Spain and to compare this with similar data for Common Coots.Methods During two consecutive breeding seasons, clutch size, egg size, brood size and chick survival of Red-knobbed and Common Coots were studied in nearly all of the lagoons in which Red-knobbed Coots were breeding.Results Clutch size was similar in the two species. Egg volume varied between years within species. Both species had similar brood sizes but chick survival differed significantly, being lower in Red-knobbed Coots (36% and 55% in 2002 and 2003, respectively) than in Common Coots (93% and 91% in 2002 and 2003, respectively). The number of fledglings per pair was lower in Red-knobbed Coots (0.9 and 2.1 in 2002 and 2003, respectively) than in Common Coots (2.2 and 3.0 in 2002 and 2003, respectively).Conclusion The disparity in productivity between Red-knobbed and Common Coots in the lagoons of southern Spain is mainly due to differential chick survival rates. These differences could be the key factor that has led to their currently different conservation status in Spain.