COS 125-5 - Locating larks: Developing a survey protocol to monitor distribution, abundance, and population trends of streaked horned larks on private lands in the Willamette Valley, OR, USA.

Abstract: Tracking the status of recovery efforts for imperiled species requires accurate information on the species’ distribution, abundance, and population trends. The streaked horned lark (Eremophila alpestris strigata) is a federally threatened songbird found in open and early successional habitats in western Washington and Oregon. More than 50% of the population is believed to breed in the Willamette Valley, OR, a region largely composed of privately-owned agricultural lands where land ownership and ephemeral habitat suitability precludes the use of existing standardized line transect survey methods successfully used elsewhere in the lark’s geographic range. To develop a protocol for monitoring the breeding population of streaked horned larks in the Willamette Valley, we implemented several steps in the design and collection of pilot data using a road-based surveys. First, we modified an existing lark habitat suitability model using a multi-year compilation of normalized difference vegetation index values across the landscape to generate spatially balanced survey points distributed within three USFWS-designated streaked horned lark recovery zones. In 2022, we conducted 8-min point count surveys at 214 points between 1 and 30 June, detecting 55 streaked horned larks at 28 points, of which 76% were male. Second, we used the initial data and challenges encountered to inform our strategy in 2023, where we completed earlier surveys (beginning 1 May) of new points. Finally, we provide a recommendation for implementing a standardized monitoring plan specific to the Willamette Valley capable of filling the knowledge gap in range-wide streaked horned lark population size and trends, which is critical to support recovery and conservation of the subspecies.