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Data for: Evaluating Golden-winged Warbler use of alder and aspen communities managed with shearing in the western Great Lakes

Citation

Buckardt Thomas, Anna (2022), Data for: Evaluating Golden-winged Warbler use of alder and aspen communities managed with shearing in the western Great Lakes, Dryad, Dataset, https://doi.org/10.5061/dryad.f4qrfj70b

Abstract

Best management practices are often written by researchers to guide land managers and landowners in the creation of habitat for wildlife species of interest. These documents are based on research evaluating the habitat needs of a species, but also describe tools and strategies managers can implement to create or restore desired conditions. Shrub and sapling shearing is a management practice often used to improve habitat for early-successional species, yet little monitoring or research has focused on wildlife response to shearing. The goal of this research was to formally evaluate the effect of shrub and sapling shearing as a best management strategy for Golden-winged Warbler (Vermivora chrysoptera) conservation at a regional scale. Specifically, we surveyed for male Golden-winged Warblers during the breeding season in sheared sites and untreated reference sites across portions of the western Great Lakes to assess the effects of 1) management status (i.e., sheared aspen or alder vs un-treated sites), and 2) the patch-level vegetation characteristics on male abundance. We found that male Golden-winged Warbler abundance was twice as high in sheared sites than in mature reference sites and peaked when sapling cover was ~40%. Male abundance was also negatively associated with percent cover of forbs and non-vegetated ground. These findings highlight the importance of patch-level heterogeneity when implementing shearing treatments for Golden-winged Warblers, and demonstrate the potential need for pre-treatment site assessments to help focus conservation efforts for this species. Ultimately, our results support the use of a site-specific, nuanced approach to shearing implementation to maximize cost efficiency and desired species outcomes.

Methods

We counted male Golden-winged Warblers at each site using a passive 10-minute point count between May 25 and July 2 each year (2012–2013, 2015–2018; n=1,222 point counts conducted). Points were visited once, annually, in 2012–2013 (n=13 points per year) and twice annually in 2015–2018 (n=68–217 points per year), and surveys were conducted in favorable weather conditions (no heavy precipitation, wind, or fog) and between 30 minutes before sunrise and five hours after sunrise. Golden-winged Warbler count data were truncated to include only males detected within 100 m, which eliminated ~3% of detections. Prior to the start of each point count, we recorded survey metadata including weather conditions (precipitation type, Beaufort wind index, percent cloud cover [0- 175 100%] rounded to the nearest 25%), point location, date, survey start time, and observer identity. Beaufort wind categories 0–2 were combined into a low wind index category and Beaufort categories 3–5 were combined to make a high wind index category for modeling. All visually and aurally detected Golden-winged Warblers were recorded as well as detection type (visual, audio, both), sex, and distance (estimated to the nearest 5m). We collected vegetation data at each location where Golden-winged Warblers were surveyed during 2015–2018 to examine relationships between male Golden-winged Warbler abundance and patch-level habitat characteristics. We sampled vegetation annually each field season from early July to August, except at reference sites which we only surveyed once under the assumption that the vegetation structure at these sites remained consistent throughout the duration of our sampling. We quantified vegetation characteristics along three 100-meter transects radiating from each point count location at 0, 120, and 240-degree azimuths. Every ten meters along each transect (n=30 locations/transect), we used an ocular tube (James and Shugart 1970) to record the presence or absence of vegetation strata: bare ground, leaf litter, graminoids (grass and sedge), forbs, ferns, Rubus, shrubs, saplings, and canopy trees. Leaf litter and bare ground strata were combined into non-vegetated strata for modeling. At the same 30 locations, we recorded the presence or absence of woody regeneration (shrubs and saplings) in four categories [none, small (0–1 m tall), medium (> 1–2 m tall), and large (> 2 m tall)] within a 1-meter radius area, for a site-level percent 199 occurrence value of each category. Although we aimed for 30 locations of sampling at each site, we truncated transect lengths when they extended beyond the boundary of a treatment footprint thus resulting in fewer than 30 subplots for some sites with irregular boundaries or a small footprint. We estimated patch-level cover and occurrence values for each vegetation component by dividing the number of subplots where a component was present by the total number of subplots sampled. Percent occurrence (measured at 1 m radius woody regeneration plots) differs from the commonly used percent cover metric (which was used for other metrics in this study) because it does not take the density of each habitat element into account, only its presence or absence throughout the site. 

Funding

United States Department of Agriculture—Natural Resource Conservation Service, Award: Agreement # 68-7482-12-502

National Institute of Food and Agriculture, Award: McIntire Stennis Project 42018

National Fish and Wildlife Foundation, Award: Agreement # 0101.14045580

Minnesota Clean Water, Land and Legacy Amendment, Award: Outdoor Heritage Fund

University of Maine Department of Wildlife, Fisheries, and Conservation Biology