Yellow-bellied Sapsuckers (Sphyrapicus varius) alter sap well locations in response to experimentally induced tree damage

Abstract

ABSTRACT Yellow-bellied Sapsuckers (Sphyrapicus varius) regularly use paper birch (Betula papyrifera) as a source of sap during the breeding season and may position their sap wells on the tree in order to maximize sap extraction. Sap flow can be affected by tree damage, and altering sap well locations in response to such damage could enhance sapsucker foraging efficiency. We sought to determine if sapsuckers selectively drilled sap wells on damaged (experimentally girdled) paper birch trees over non-damaged healthy trees and, if so, whether the locations of the drill sites varied in response to this damage. Sapsuckers drilled holes on a significantly larger proportion of girdled trees than control trees (healthy trees on adjacent plots), and the holes were lower on girdled trees in comparison with control trees. These differences occurred even though control and girdled trees were of similar size (diameter) and had similar numbers of sap wells per tree. Yellow-bellied Sapsuckers appear to alter their fora...