Columbia River Streaked Horned Lark Surveys and Monitoring Final Report 2014

The Center for Natural Lands Management (CNLM) has been monitoring larks in the lower Columbia River since 2010. Within the Columbia River there are a series of islands created through periodic placement of dredged materials that provide suitable habitat for larks. However, deposition islands appear to be suitable for a limited period, apparently from 2-3 years after creation until 7-8 years after creation (Anderson 2013). Understanding lark distribution is key to minimizing impacts from deposition actions as well as maximizing the habitat creation benefits of dredged material placement. In addition, monitoring lark distribution and trends through time can help us understand how larks are responding to deposition actions.

In 2014, we continued ongoing efforts and initiated new components; overall, we focused on five objectives. The first objective was to determine occupancy at deposition islands that had never been previously surveyed for larks or sites where larks had not recently been detected. Because the proposed abundance monitoring protocol, drafted by WDFW (2012) relies on counts at occupied sites, periodic assessment of unsurveyed sites is important to determine if they should be included in the abundance monitoring network and to inform potential deposition actions at these sites.

The second and third objectives were related to abundance monitoring efforts that have been ongoing since 2010. Long-term monitoring of lark abundance is key to assess the species conservation status, evaluate management efforts, and measure long-term population trends. Objective Two (or 2) was to conduct a pilot study to estimate lark detectability. This new project was initiated because we know that lark surveys have imperfect detection and understanding detectability and how it varies is critical to evaluating long-term trends in abundance. For example, some birds are missed because they didn’t sing or an observer may have been looking the other way when an individual made a movement in their territory. Estimating detectability is also critical for use by the Washington Department of Fish and Wildlife (WDFW) to get a more precise estimate of population trend. WDFW intends to use an N-mixture model approach (Royle et al. 2004) in which prior estimates of detection probability is critical for conducting this analysis. We estimated detectability using Distance sampling, which is a well-established method (Buckland et al. 2001). The third objective was to continue monitoring larks on occupied deposition sites using the WDFW lark monitoring protocol. We also evaluated patterns of lark abundance over time to describe notable patterns in abundance.

The fourth objective was to qualitatively assess habitat for larks at the sites visited in Objectives 1 and 3. These assessments can be used by managers to determine future management (e.g., deposition) considerations. Finally, we make recommendations about future monitoring.