The diet of the night heron and a purple heron in the Guadalquivir marshes

Abstract

The diet of the night heron and purple heron in the Guadalquivir Marshes. Aims: To compare the diet of chicks of night heron Nycticorax nycticorax and purple heron Ardea Pur- purea in the Guadalquivir Marshes. To study the diet of night heron adults during breeding and non-breed- ing seasons. To establish whether the diet of purple heron in Doñana has changed over the past 30 years in response to changes in land use and habitat quality. Location: Heronries in the Guadalquivir Marshes, including the natural marshes of Doñana National Park and transformed marshes dominated by ricefields outside the National Park. Methods: Collection of regurgitates from purple heron chicks (n = 52) and night heron chicks (n = 12) during ringing operations in 2001-2002. Collection of pellets (n = 80) under daytime roosts of night herons in 2001-2002. Results: Purple heron regurgitates were dominated by carp Cyprinus carpio, recorded in 84.6 % of samples and representing 73.3 % of all prey items. Odonata nymphs were present in 13.5 % of samples and aquatic Coleoptera in 9.6 %. Regurgitates from night heron chicks were also dominated by carp, record- ed in 83.3 % of the samples and representing 76.3 % of prey items. Coleoptera larvae were present in 25 % of samples. There was no difference in the size of carp consumed by the two species, but carp taken by purple heron were larger in 2002. Night heron pellets collected outside the breeding colonies lacked fish and were dominated by red swamp crayfish Procambarus clarkii, present in 86.2 % of pellets and repre- senting 44.4 % of prey items. Terrestrial insects were also abundant in pellets. Conclusions: In spite of the great increase in abundance of P. clarkii in natural marshes since earlier studies in 1977-1983, and other major changes in the ecosystem, there has been no detectable change in purple heron diet over this period. Night heron and purple heron chicks in Doñana fed prodominantly on an invasive fish. Outside the breeding colonies, night herons fed predominantly on an invasive crayfish. Key words: Doñana, ecological change, food items, night heron, purple heron

La dieta del martinete y la garza imperial en las marismas del Guadalquivir. Objetivos: Comparar la dieta de los pollos de martinete Nycticorax nycticorax y garza imperial Ardea purpurea en las marismas del Guadalquivir. Estudiar la dieta de los adultos de martinete durante el pe- riodo reproductor y no reproductor. Determinar si la dieta de la garza imperial en Doñana ha cambiado a lo largo de los últimos 30 años, debido a cambios en los usos del suelo y la calidad del hábitat.