Sources of Variation in the Abundance and Detection of the Endangered Florida Grasshopper Sparrow

Abstract

Unmarked aims to be a complete environment for the statistical analysis of data from surveys of unmarked animals. Currently, the focus is on hierarchical models that separately model a latent state (or states) and an observation process. This vignette provides a brief overview of the package -for a more thorough treatment see [2] 1 Overview of unmarked Unmarked provides methods to estimate site occupancy, abundance, and density of animals (or possibly other organisms/objects) that cannot be detected with certainty. Numerous models are available that correspond to specialized survey methods such as temporally replicated surveys, distance sampling, removal sampling, and double observer sampling. These data are often associated with metadata related to the design of the study. For example, in distance sampling, the study design (line-or point-transect), distance class break points, transect lengths, and units of measurement need to be accounted for in the analysis. Unmarked uses S4 classes to store data and metadata in a way that allows for easy data manipulation, summarization, and model specification. Table 1 lists the currently implemented models and their associated fitting functions and data classes.

Accounting for misclassification of subspecies provides insights about habitat use and dynamics of the Florida Grasshopper Sparrow in response to fire

“…Point count surveys for the Florida Grasshopper Sparrow generally start in late March or early April, at the start of their breeding season, thus in some years there may be as much as a month when males of both subspecies are singing. Point count surveys conducted after eastern Grasshopper Sparrows leave in May have a higher certainty of detection but also may be less likely to detect Florida Grasshopper Sparrows given lower levels of nesting synchrony and singing at that point in the breeding season (Delany et al 2013, Lohr et al 2013. Explicitly modeling certainty of detections and misclassifications allows for surveys to be completed at the most likely time to detect Florida Grasshopper Sparrow while also accounting for the presence of the eastern Grasshopper Sparrow.…”

“…We did not truncate Florida Grasshopper Sparrow detections at any distance to maintain consistency among years of study, because most point count surveys did not record distance to detection. Florida Grasshopper Sparrows have high-pitched (~ 8 kHz) songs that are difficult for human listeners to hear at great distances, and previous studies suggest a detection radius of < 200 m (Delany et al 2013).…”

Optimizing reproductive opportunity for Florida grasshopper sparrows: When to burn?

“…We located territories of male Florida grasshopper sparrows by re‐sighting color bands and monitoring birds detected during annual point count surveys (400 m apart) across the entire study area (Delany et al ). We visited males frequently for territory mapping and nest searching activities.…”

Exclosure fences around nests of imperiled Florida Grasshopper Sparrows reduce rates of predation by mammals

“…We located territories of male Florida Grasshopper Sparrows each breeding season (March–August) by monitoring color‐banded birds detected during annual point count surveys (Delany et al. ) at Three Lakes (2013–2018) and the Ranch (2015–2016). We visited territories frequently and located nests primarily through behavioral observations of breeding adults and, occasionally, when females flushed when we walked through their territory (Aldredge ).…”