La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	Detection ratios on winter surveys of Rocky Mountain Trumpeter Swans Cygnus buccinator
Auteurs :	Jonathan Bart, Auteur ; Carl D. Mitchell, Auteur ; Michael N. Fisher, Auteur ; James A. Dubvsky, Auteur
Type de document :	Article
Dans :	Wildfowl (57 2007)
Article en page(s) :	21-28
Langues:	Anglais
Résumé :	We estimated the detection ratio for Rocky Mountain Trumpeter Swans Cygnus buccinator that were counted during aerial surveys made in winter. The standard survey involved counting white or grey birds on snow and ice and thus might be expected to have bad low detection ratios. On the other hand, observers were permitted to circle areas where the birds were concentrated multiple times to obtain accurate counts. Actual numbers present were estimated by conducting additional intensive aerial counts either immediately before or immediately after the standard count. Surveyors continued the intensive surveys at each area until consecutive counts were identical. The surveys were made at

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