Notch factor - A technique for separating Marsh Warblers Acrocephalus palustris from Reed Warblers A. scirpaceus on spring migration

Abstract

Using measurements which are regularly collected on Reed Acrocephalus scirpaceus and Marsh Warblers Acrocephalus palustris, a new method was tested which appears to give better separation than the currently available biometric techniques. The length of the notch on the inner web of the second primary is multiplied by the number of the primary whose tip it falls adjacent to (numbering ascendently) to calculate the ‘notch factor’. This factor successfully separated (on biometrics alone) 1, 574 out of 1, 577 birds trapped in the spring migration through Kuwait. Reed Warblers trapped represented individuals from both the scirpaceus and fuscus races. © 2001 British Trust for Ornithology.