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

Timothy D Meehan,Håvard Rue,Nicole L Michel

doi:10.1002/ecs2.2707

Timothy D Meehan, Håvard Rue + Show 1 more

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https://doi.org/10.1002/ecs2.2707

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Abstract

AbstractBird 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.

Highlights

Volunteers with the Audubon Christmas Bird Count (CBC) have been counting wintering birds across North America every year for the last 118 yr (Dunn et al 2005, Soykan et al 2016)
Population trends derived from CBC data, along with those derived from other large-scale monitoring programs like the North American Breeding Bird Survey (BBS, Robbins et al 1989, Sauer et al 2017), provide valuable information for understanding the conservation needs of North American bird species (Dickinson et al 2010, Hochachka et al 2012)
The four goals of this report were to (1) describe an spatially varying coefficient (SVC) approach for calculating trends in CBC data, (2) employ the approach using data for the American Robin (Turdus migratorius), (3) compare trend results derived from the SVC approach to those derived from standard methods, and (4) demonstrate use of fine-scaled trend results through a simple post hoc analysis exploring correlations between precomputed SVC trends and potential energetic drivers related to climate and winter food resources

Summary

Introduction

Volunteers with the Audubon Christmas Bird Count (CBC) have been counting wintering birds across North America every year for the last 118 yr (Dunn et al 2005, Soykan et al 2016). Treating each stratum as independent, a non-linear function is used to correct for the effect of observer effort on counts, while simultaneous effects are estimated for the impact of count circle, year, and stratum by year (Link et al 2006, Soykan et al 2016) These parameter estimates are used to derive a relative abundance index per stratum and year, and those annual indices are used to compute annual percent change per stratum across defined time periods (Link and Sauer 2002, Sauer and Link 2011)

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