Cerulean Warbler (Setophaga cerulea) Use of Managed Forests Enrolled in Private Lands Conservation Programs in Pennsylvania and Western Maryland

Abstract

The Cerulean Warbler (Setophaga cerulea) is a migratory songbird exhibiting one of the most dramatic and sustained population declines of all eastern forest birds by 1.9%, annually. Population declines for this species are understood to be driven, in large part, by breeding habitat loss. Indeed, the structurally-complex forest required by nesting Cerulean Warblers have become increasingly rare in eastern forests. In 2013, science-informed best management practices (BMPs) were created that described a series of silvicultural techniques to enhance Cerulean Warbler nesting habitat in the Appalachian Mountains. From 2016-2020, Natural Resources Conservation Service and several partners implemented these BMPs across more than 3,800 ha of private forest lands. Understanding how Cerulean Warblers respond to conservation efforts on private lands is important given that >70% of Appalachian forests are privately-owned. I used single-season occupancy models to evaluate Cerulean Warbler response to management and habitat features on private forests enrolled in NRCS programs in Pennsylvania and western Maryland. From 2017-2020, I conducted 684 avian point counts and 342 vegetation surveys across 139 unique locations. Study sites were either pre-treatment (n=56) or post-treatment (n=104). Across all sites, mean Cerulean Warbler occupancy probability was low (0.16; 95%CI: 0.10- 0.23). Site occupancy was best explained by distance to nearest known Cerulean Warbler population. Although sites were managedusing species-specific best management practices, low Cerulean Warbler occupancy was likely driven by poor pre-existing forest conditions at treated sites. Indeed, both DBH (median = 34.7 cm; 95%CI: 32.3- 35.9) and basal area (median = 23.5 m2/ha; 95%CI: 20.7- 23.7) were relatively low for pre-treatment, mature forests and left limited room for short-term improvement. Such conditions are characteristic of prior unsustainable harvest practices (e.g., high grading) that commonly occur on private lands in eastern deciduous forests. Future efforts to implement Cerulean Warbler BMP guidelines should prioritize sites that are proximate to existing Cerulean Warbler breeding populations. Even then, managers should recognize that a legacy of exploitative timber harvests on private land may prevent the near-term attainment of some habitat targets important for Cerulean Warbler occupancy (i.e., DBH ≥ 40.6 cm), and thus likely limit colonization of managed stands by the species.