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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	A field test of the distance sampling method using Golden-cheeked Warblers
Auteurs :	Rebecca G. Peak, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (82(3) SEP 2011)
Article en page(s) :	311-319
Langues:	Anglais
Résumé :	Criteria for delisting Golden-cheeked Warblers (Dendroica chrysoparia) include protection of sufficient breeding habitat to ensure the continued existence of 1000 to 3000 singing males in each of eight recovery regions for >= 10 consecutive years. Hence, accurate abundance estimation is an integral component in the recovery of this species. I conducted a field test to determine if the distance sampling method provided unbiased abundance estimates for Golden-cheeked Warblers and develop recommendations to improve the accuracy of estimates by minimizing the effects of violating this method's assumptions. To determine if observers could satisfy the assumptions that birds are detected at the point with certainty and at their initial locations, I compared point-transect sampling estimates from 2-, 3-, 4-, and 5-min time intervals to actual abundance determined by intensive territory monitoring. Point-transect abundance estimates were 15%, 29%, 43%, and 59% greater than actual abundance (N = 156) for the 2-, 3-, 4-, and 5-min intervals, respectively. Point-transect sampling produced unbiased estimates of Golden-cheeked Warbler abundance when counts were limited to 2 min (N = 154-207). Abundance estimates derived from point-transect sampling were likely greater than actual abundance because observers did not satisfy the assumption that birds were detected at their initial locations due to the frequent movements and large territory sizes of male Golden-cheeked Warblers. To minimize the effect of movement on abundance estimates, I recommend limiting counts of singing males to 2-min per point. Counts for other species in similar habitats with similar behavior and movement patterns also should be limited to 2 min when unbiased estimates are important and conducting field tests of the point-transect distance sampling method is not possible.

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