A Comparison of Acoustic and Point Count Monitoring with Respect to Historical Records to Determine Avian Migration Phenology in the Great Plains

Pavlacky, D.C.Jr

In 2011, the Desert Southwest Cooperative Ecosystem Studies Unit, the National Park Service, and Rocky Mountain Bird Observatory initiated a project comparing acoustic and point count monitoring techniques to investigate the migration phenology of grassland birds. A goal of the project was to determine if climate change was responsible for declines in grassland bird species by causing a mismatch in spring arrival dates and food availability. Another goal of the study was to measure the effectiveness of automated recording units for surveying birds. Automated recording units were deployed at four study sites (Badlands and Wind Cave National Parks in South Dakota and Lake Meredith National Recreation Area and Rita Blanca National Grassland in Texas) and point count surveys were conducted at the same locations to compare the two methodologies during 2011 and 2012 field seasons. We used 15 years of eBird data to investigate temporal and spatial trends in the arrival dates of the grasshopper sparrow in the Great Plains. We discovered that the detection rates of acoustic monitoring units and point counts were similar for the long-billed curlew, Cassin’s sparrow, grasshopper sparrow and brown-headed cowbird. In contrast, the detection rates for the acoustic method were lower than the point count method for the vesper sparrow, lark sparrow and lark bunting. Acoustic monitoring performed equal to point count methods for estimating the arrival dates of the grasshopper sparrow, lark sparrow and lark bunting. Conversely, acoustic monitoring detected arrival on the breeding grounds before the territorial establishment of the long-billed curlew, Cassin’s sparrow and brown-headed cowbird. Interestingly, acoustic monitoring detected arrival on the breeding ground after territorial establishment of the vesper sparrow. Our results suggested that the grasshopper sparrow may be able to alter migration timing to match early onset of spring conditions. Because this species demonstrated flexibility in migration timing, climate change and associated changes to the timing of resource availability may not be a large contributor to ongoing population declines of this species.

A Comparison of Acoustic and Point Count Monitoring with Respect to Historical Records to Determine Avian Migration Phenology in the Great Plains

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