Submersed macrophytes as a food source for wintering waterbirds at Lake Constance

We investigated the relationship between Charophytes and herbivorous waterbirds in the littoral zone of Lake Constance by quantifying their seasonal dynamics. The waterfowl extensively consumed Charophyte vegetation in shallower areas (<1 m water depth) at the beginning of the winter season, while deeper regions were only used in late winter. By the end of winter, the waterfowl had almost completely depleted the available Charophyte biomass down to a water depth of approximately 2 m (relative to average mean water level (AML)). Enclosure experiments revealed that senescence processes had a negligible influence on Charophytes biomass loss until early February. Coot, Red-crested Pochard and Pochard are the main avian Chara consumers in winter. Despite their great influence on biomass in winter, their influence on subsequent Charophyte regeneration is probably limited in Lake Constance, since Charophytes as typical pioneer species produce innumerable diaspores forming dense Charophyte meadows at a depth of between 1 and 4 m every year.     

Response of waterbirds to alternating clear and turbid water phases in two shallow Mediterranean lakes

Albufera de Adra (Southern Spain) constitutes an internationally-recognised marsh for waterbirds; important populations of some endangered species such as White-headed Duck and Red-crested Pochard overwinter and breed in its two shallow permanent lakes (Lake Honda and Lake Nueva). In a recently published article, we revealed the factors responsible for the irregular alternation between phytoplankton-dominated turbid phases and macrophyte-dominated clear water phases in Lake Honda and Lake Nueva. In this note, we try to clarify the impact of such an alternation of equilibrium states on the waterbird dynamics. Marked increments in abundance, and brood recruitment of dabbling and diving waterbirds were recorded during the clear water phases in contrast with the turbid water phases, as the increase of macrophytes associated with increased water transparency attract waterbirds for available food. Implications for ecosystem management, restoration and conservation are identified.     

Winter distribution and population change of Red-crested Pochard Netta rufina in southwestern and central Europe

Under the African-Eurasian Waterbird Agreement (AEWA) of the Convention on Migratory Animals (Bonn Convention), the Red-crested Pochard Netta rufina has a high conservation priority in Europe. This is particularly the case for the southwest/central European flyway population, which is considerably smaller than the southeast European and Asian ones. Data from the International Waterbird Census from 1967 to 1994 indicate that the flyway population has remained at a similar level between the mid-1980s and mid- 1990s, but is likely to be smaller than it was in the 1970s. Population size in January is estimated to be between 25 000 and 30 000 individuals. In winter, the Red-crested Pochard is concentrated at a small number of sites. In the period 1985–94, 75% of the population were observed at the six main sites: Laguna de Gallocanta, Albufera de Valencia, Delta del Ebro, Marismas del Guadalquivir (all in Spain), Camargue (France) and Lac de Neuchâtel (Switzerland). In January, 39 sites held ≥1% of the population at least once between 1975 and 1994. The Red-crested Pochard has recently shown a marked change in its winter distribution, and two patterns emerged: (1) a shift from the western Mediterranean to the region north of the Alps; and (2) the use of a greater number of sites.