Comparing census methods for the endangered Kirtland's Warbler

Abstract

Abstract We compared transect counts used for the annual official count of male Kirtland's Warblers (Dendroica kirtlandii) to an observation-based mapping method of individually sighted males in 155 stands over 10 yrs. The annual census count almost tripled from 1990 to 1999. The transect and observation-based mapping method showed the same increasing trend in population between 1990 and 1999, except from 1992 to 1993. The annual official census transect count was consistently higher than the mapping method for stands censused in common. After standardizing for sample size, the annual number of Kirtland's Warblers per stand increased through time with the transect method, while there was a positive, non-significant trend with the mapping method. After 1992, the two methods began diverging in the number of males per stand. The relationship between the differences in count between methods (mapping count minus transect count) to the official transect count varied among years. At the stand level, the transect...