Plant-water regime management in a wetland: consequences for a floating vegetation-nesting bird, whiskered tern Chlidonias hybridus

Abstract

In this study we investigated the interplay between water level management, floating macrophytic vegetation and nesting whiskered tern (Chlidonias hybridus) during 8 years (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002) at a shallow macrophyte-dominated lake in western France. The specific question was to see if slight increases in the water regime of the lake (three scenarios), as part of a restoration programme, affect the timing of nesting and occupation of colonies by whiskered terns by way of changes in biomass of waterlily (Nymphaea alba) beds where colonies always establish. During the study period, egg-laying dates were progressively delayed up to 40-50 days (mid-May to early July) in relation to late appearance of suitable waterlily biomass (R 2 = 0.67, p = 0.01) associated with high spring water levels (1.10-1.25 m vs. 0.95 m). Simultaneously some nesting attempts were observed in sub-optimal habitats (adjacent wet grasslands) in high flooding conditions leading either to poor breeding success or colony desertion. We concluded that there is a need for compromise between the experimental water levels used to control waterlily biomass and the nesting requirements of the whiskered tern population in this lake of international importance (260-510 pairs in 1995(260-510 pairs in -2002.

Reproductive parameters in relation to food supply in the whiskered tern (Chlidonias hybrida)

“…In contrast, they laid slightly earlier in 2005 than in 2004. Moreover, the timing of laying in whiskered terns has been found to be strongly affected by other proximate factors, such as the development of floating plant beds and the water level conditions (Paillisson et al 2006). However, we found no sign that the development of waterlily beds in 2005 had a positive effect in enabling the birds to breed early in 2005 despite the food shortage.…”

“…Despite its unfavourable conservation status in Europe (Tomialojc 1994), the whiskered tern has been little studied (Spina 1982), although recently it has been the focus of two studies (Bakaria et al 2002;Paillisson et al 2006). …”

“…Lake Grand-Lieu currently supports a whiskered tern breeding population ranging from 620 to 1250 pairs breeding at 10-11 colonies. Nesting platforms are always built on waterlily beds and consist mainly of waterlily leaves and stems and common clubrush Scirpus lacustris stems (Paillisson et al 2006).…”

Estimation of ecological water requirements based on habitat response to water level in Huanghe River Delta, China

“…All coastal or shoreline wetland plant communities have one or more bird habitats influenced by water depth and flood duration (Desgranges et al, 2006). Slight increases in the water level of wetlands could progressively delay the egg-laying dates of birds (for example, Chlidonias hybrida) up to 40-50 days in relation to late appearance of suitable aquatic biomass (Pallisson et al, 2006). Although the hydrological conditions greatly influence the nature of plant growth and bird distribution in wetlands, it is unknown how hydrology interacts with the other features of plant growth, e.g.…”

Effect of seasonal water level decrease on a sensitive bird assemblage in a Mediterranean wetland

“…Some studies were undertaken with regard to the direct and/or indirect effects of natural or human-induced water stress on target species (e.g., Kushlan et al 1975;Cézilly et al 1995;Strong et al 1997;Báldi and Kisbenedek 1998;Arengo and Baldassarre 1999;Boertmann and Ricet 2006;Paillisson et al 2006) and on bird assemblages at pluriannual scale (Battisti et al 2004. Nevertheless, investigations on seasonal changes of bird assemblages are lacking, especially in remnant wetlands where consequences may be emphasized (Saunders et al 1991;Leibowitz 2003).…”