Budworm-linked warblers as early indicators of defoliation by spruce budworm: A field study. (June 2021)

• Record Type: Journal Article
• Authors: Moisan Perrier, Jeanne; Kneeshaw, Daniel; St-Laurent, Martin-Hugues; Pyle, Peter; Villard, Marc-André
• Is Part Of: Ecological indicators. Volume 125(2021)
• Publication Date: 2021-06
• Subjects: Boreal forest -- Despotic behavior -- Dispersal -- Herbivorous insects -- Early intervention strategies -- Insect outbreaks; Environmental monitoring -- Periodicals; Environmental management -- Periodicals; Environmental impact analysis -- Periodicals; Environmental risk assessment -- Periodicals; Sustainable development -- Periodicals; 333.71405
• DOI: 10.1016/j.ecolind.2021.107543
• Languages: English
• ISSNs: 1470-160X

Abstract

Highlights: Bay-breasted Warbler responded fastest to an increase in the density of spruce budworm larvae. Bay-breasted Warblers breeding for the first time colonized stands at earlier stages of infestation. Experienced Bay-breasted Warblers dominated stands with high spruce budworm densities. Bay-breasted Warbler is a reliable indicator to guide early intervention strategies to control spruce budworm. Abstract: Outbreaks of eastern spruce budworm ( Choristoneura fumiferana ; hereafter SBW) are a major natural disturbance in coniferous forests of eastern North America. These outbreaks provide a superabundant source of food for insectivorous birds. Three species, referred to as budworm-linked warblers, exhibit strong positive numerical responses to early increases of SBW density: Tennessee Warbler ( Leiothlypis peregrina ), Cape May Warbler ( Setophaga tigrina ), and Bay-breasted Warbler ( S. castanea ). Their abundance increases even before defoliation is visible from aerial surveys. Budworm-linked warblers may detect new epicenters of SBW outbreaks through natal dispersal, as this movement is typically much more extensive than subsequent (breeding dispersal) movements. Our main objectives were, thus, (1) to determine whether sudden increases in the abundance of budworm-linked warblers could be used to detect early stages of SBW outbreaks, and (2) to examine age-specific responses of budworm-linked warblers to local and landscape-level habitat characteristics, in order to investigate the potential role of natal dispersal in the detection of new epicenters. To do so, we estimated the abundance of each species of budworm-linked warbler in 75 study plots sampling a gradient of SBW density and related them to 7 stand variables and landscape metrics with generalized additive mixed models. We also compared the responses of yearling (second-year; SY) and older (after-second-year; ASY) individuals to the density of SBW larvae and habitat variables at different spatial scales. We captured 31 Tennessee Warblers, 27 Cape May Warblers, and 57 Bay-breasted Warblers. The abundance of all three species of budworm-linked warblers increased with SBW larval density, but the numerical response of Bay-breasted Warbler was initiated earlier and it varied with age. SY individuals tended to be associated with stands supporting lower larval densities than ASY individuals and, as suggested by other authors, Bay-breasted Warbler appeared to be more efficient at exploiting SBW larvae at low density. For that reason, this species represents an early indicator of stands undergoing SBW outbreaks and we propose to use its abundance as an indicator to orient labour-intensive ground surveys of SBW larvae.