Effects of Rice Field Water Cycles on the Breeding Biology of Grey Heron (Ardea cinerea) and Conservation Implications

Abstract. Wetlands are among the most threatened ecosystems on the planet, largely due to their conversion to agricultural or dry land. L'Albufera de Vàlencia is characterized by a large expanse of rice fields (c. 14,000 ha), which hosts the most important colony of Grey Heron Ardea cinerea on the Mediterranean coast of Spain. The colony was visited every 10 days during February-April of 2016 to 2018 and during May-July of 2015 to 2017. The reproductive parameters were estimated for each year and season. We also monitored the available habitat and habitat use of the species in the rice fields from February 2016 to June 2017. The condition of the rice field was related to reproductive parameters. The breeding period was divided into two stages per year. In 2016 all reproductive parameters were lower values, coinciding with a larger area of dry fields in winter and low rainfall in summer. Breeding success was found to be positively associated with the muddy/semi-flooded fields and negatively associated with the sown fields. Like Grey Heron, other waterbirds species nesting in L'Albufera de Valencia could depend on the condition of the rice fields for breeding success. Their reproductive requirements should be considered in rice cultivation management.