Response of corvid nest predators to thinning: implications for balancing short- and long-term goals for restoration of forest habitat

Abstract

Forest thinning on public lands in the Pacific Northwest USA is an important tool for restoring diversity in forest stands with a legacy of simplified structure from decades of intensive management for timber production. A primary application of thinning in young (< 50-year-old) stands is to accelerate forest development to mitigate loss of late-seral habitat to decades of logging. However, thinning may have short-term negative effects for some species associated with mature forest that are expected to benefit from the practice over the long term. An increased risk of nest predation is a primary concern to managers charged with stewardship of habitat for the federally threatened Marbled Murrelet (Brachyramphus marmoratus), a species that nests in older forests. Predation by corvids is the greatest cause of nest failure for the Marbled Murrelet, and corvids are known to respond positively to forest disturbance, but quantitative information is lacking on the potential impacts of thinning on risk of nest predation. We investigated the response of two common corvid nest predators, Steller's Jay (Cyanocitta stelleri) and Canada Jay (Perisoreus canadensis), to variation in thinning intensity in young forest (< 50 years old) using data from a long-term silviculture experiment. We used a Before-After-Control-Impact (BACI) design, linear mixed modeling, and occupancy modeling to quantify differences in corvid observation rates among varying levels of thinning intensity, and to assess changes in jay response over more than a decade following thinning. We found an increase in observation rates of both species in the heavily thinned treatment during the first 5 to 7 years following thinning, and some evidence of a shortterm increase in Steller's Jay activity in the thinning-with-gaps treatment. Neither jay species responded to the least intensive thinning treatment, which reduced average canopy cover by < 30%. By approximately a decade after thinning, observation rates of jays did not differ between unthinned controls and any of the thinning treatments. Incorporating our quantitative information into landscape-level planning can help managers balance short-and long-term conservation goals.Réaction de corvidés prédateurs de nids à l'éclaircie : répercussions pour obtenir un équilibre entre les objectifs à court et à long termes de la restauration de l'habitat forestier RÉSUMÉ. L'éclaircie forestière sur les terres publiques du nord-ouest des États-Unis est un outil important visant à restaurer la diversité dans les peuplements forestiers dont la structure a été simplifiée par des décennies d'aménagement intensif destiné à la production de bois. L'un des principaux objectifs de l'éclaircie de jeunes peuplements (< 50 ans) est d'accélérer la croissance de la forêt afin d'atténuer la perte d'habitat de stades successionnels avancés attribuable à des décennies d'exploitation forestière. Cependant, l'éclaircie peut avoir des effets négatifs à court terme pour certaines espèces associées aux forêts matures qui devraient bénéficier ...