Spatial modeling of Audubon Christmas Bird Counts reveals fine‐scale patterns and drivers of relative abundance trends

Abstract

Bird counts by community volunteers provide valuable information about the conservation needs of many bird species. The statistical modeling techniques commonly used to analyze these counts provide robust, long‐term population trend estimates from heterogeneous community science data at regional, national, and continental scales. Here, we present a new modeling approach that increases the spatial resolution of trend estimates and reduces the computational burden of trend estimation, each by an order of magnitude. We demonstrate the approach with data for the American Robin (Turdus migratorius) from Audubon Christmas Bird Counts conducted between 1966 and 2017. We show that aggregate regional trend estimates from the proposed method aligned well with those from the current standard method, and that spatial variation in trends was associated with winter temperatures and human population densities as predicted by ecological energetics. This technique can provide reasonable large‐scale trend estimates for users interested in general patterns, while also providing higher‐resolution estimates for examining correlates of abundance trends at finer spatial scales, which is a prerequisite for tailoring management plans to local conditions.

Modeling avian full annual cycle distribution and population trends with citizen science data

“…The spatially and seasonally explicit trend estimates also provide new information about interannual changes in Wood Thrush population size. The spatial resolution of the trend estimates presented here is relatively high compared to other studies with similarly broad spatial extents (Sauer et al 2017, Baker et al 2019, Meehan et al 2019, Rushing et al 2019. Both breeding and non-breeding trend maps show significant spatial variation in the pattern of declines, with the steepest declines within the 5% FDR regions (Figs.…”

“…) and with the North American Christmas Bird Count (Meehan et al. ). To match the common terminology in the literature, we will also refer to this as an estimate of relative abundance.…”

“…Similarly, the expected count of individuals of the species on the same standardized checklist is a measure of relative abundance, an index of the total count of the individuals of the species present in the search area. Note that this measure of abundance is equivalent in many respects to the relative abundance estimates used to estimate trends with the North American Breeding Bird Survey (BBS; Link 2011, Sauer et al 2017) and with the North American Christmas Bird Count (Meehan et al 2019). To match the common terminology in the literature, we will also refer to this as an estimate of relative abundance.…”

“…, and Meehan et al. ) across broad spatial extents have turned to the use of less structured survey data collected by citizen scientists. Citizen science projects have been very successful at collecting species observation data with high spatial and temporal resolution across broad extents throughout the year (Dickinson et al.…”

“…Recent efforts to estimate species' distributions (K ery et al 2010), abundance (Johnston et al 2015), and trends (Horns et al 2018, Baker et al 2019, and Meehan et al 2019) across broad spatial extents have turned to the use of less structured survey data collected by citizen scientists. Citizen science projects have been very successful at collecting species observation data with high spatial and temporal resolution across broad extents throughout the year (Dickinson et al 2010).…”