Bibliothèque Tour du Valat

Se connecter

Mot de passe oublié ?
Pas encore inscrit ?

La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Détail

Ajouter au panier

Ajouter au panier

Lien vers la notice

Titre :	[Bewick's Swans in the IJsselmeer area. Have the good times passed?] (2002)
Auteurs :	Ruurd Noordhuis, Auteur ; Ingrid Tulp, Auteur
Type de document :	Article
Dans :	Limosa (75(1) 2002)
Article en page(s) :	13-24
Résumé :	Brouwer and Tinbergen (1939) described the changes in distribution of Bewick's Swans when eelgrass (Zostera sp.) disappeared and pondweeds (Potamogeton pectinatus) spread over the area after the formerly brackish Zuiderzee was dammed in 1932 and turned fresh afterwards. Since then, several other changes took place in the area. About half of the newly formed Lake IJsselmeer was reclaimed and water quality changed as a result of eutrophication. Algal blooms developed and in Lake Veluwemeer, by then the most important foraging area for Bewick's Swans outside the dikes, all macrophytes disappeared around 1970, except for P. pectinatus. While most other species disappeared for lack of food, Bewick's Swans kept appearing each year of feed on the tubers of this pondweed. In the second half of the 1980s, macrophytes started to respond to measures to improve water quality. At first pondweeds increased, but they were pushed to deeper areas as stoneworts Chara spp. reappeared and spread to cover large areas during the 1990s. Bewick's Swans switched to stoneworts for food and reached higher numbers than before. However, Mute Swans also increased, both in winter and during the moulting season. Due to their smaller size and tendency to focus on underground parts of the stoneworts, Bewick's Swans need shallower waters and are more susceptable to water level changes than Mute Swans. In recent years, Mute Swan numbers have increased particularly in the moulting season. As a result, an increasing share of the available biomass of stoneworts is consumed before the Bewick's Swans appear in October. Since autumn 1999 Bewick Swan numbers have remained low. Along with other factors like an overall population decrease and a relatively poor food quality this may have been caused by competition between the two species.

FAQ

Infos pratiques

Heures d'ouverture et contact

Lundi , mardi et jeudi de 9h à 12h et de 13h à 17h00 : ouverture au public ...

Liens utiles

A-
A
A+