Recent stability of resident and migratory landbird populations in National Parks of the Pacific Northwest

Abstract

Abstract. Monitoring species in National Parks facilitates inference regarding effects of climate change on population dynamics because parks are relatively unaffected by other forms of anthropogenic disturbance. Even at early points in a monitoring program, identifying climate covariates of population density can suggest vulnerabilities to future change. Monitoring landbird populations in parks during the breeding season brings the added benefit of allowing a comparative approach to inference across a large suite of species with diverse requirements. For example, comparing resident and migratory species that vary in exposure to non-park habitats can reveal the relative importance of park effects, such as those related to local climate. We monitored landbirds using breeding-season point-count data collected during 2005-2014 in three wilderness areas of the Pacific Northwest (Mount Rainier, North Cascades, and Olympic National Parks). For 39 species, we estimated recent trends in population density while accounting for individual detection probability using Bayesian hierarchical N-mixture models. Our analyses integrated several recent developments in N-mixture modeling, incorporating interval and distance sampling to estimate distinct components of detection probability while also accommodating count intervals of varying duration, annual variation in the length and number of point-count transects, spatial autocorrelation, random effects, and covariates of detection and density. As covariates of density, we considered metrics of precipitation and temperature hypothesized to affect breeding success. We also considered effects of park and elevational stratum on trend. Regardless of model structure, we estimated stable or increasing densities during 2005-2014 for most populations. Mean trends across species were positive for migrants in every park and for residents in one park. A recent snowfall deficit in this region might have contributed to the positive trend, because population density varied inversely with precipitation-as-snow for both migrants and residents. Densities varied directly but much more weakly with mean spring temperature. Our approach exemplifies an analytical framework for estimating trends from point-count data, and for assessing the role of climatic and other spatiotemporal variables in driving those trends. Understanding population trends and the factors that drive them is critical for adaptive management and resource stewardship in the context of climate change.

Explaining the birds and the bees: deriving habitat restoration targets from multi‐species occupancy models

“…, Ray et al. ). Each survey lasted 7 min and was divided into three consecutive time intervals: a 3‐min period and then two subsequent 2‐min periods.…”

“…To maximize the number and diversity of sites sampled, we allocated our bird sampling effort to visit each site once between late May and early July in both years, rather than visiting a smaller number of sites multiple times (MacKenzie and Royle 2005). Breeding territories of landbirds are typically stable throughout the seasonal period of our study, allowing strong inferences based on a single site visit (Tingley et al 2016, Ray et al 2017. Each survey lasted 7 min and was divided into three consecutive time intervals: a 3-min period and then two subsequent 2-min periods.…”

Landbird trends in protected areas using time‐to‐event occupancy models

“…Bird responses to climate change may depend on their life history strategies (e.g., specialists vs generalists and migratory vs resident). This variability among species and regions creates challenges when trying to tease apart the effects of climate change and other landscape changes (Ray et al 2017, Scridel et al 2018, Clement et al 2019.…”

“…Some mountainous bird populations maintain their climatic niche by shifting their range upslope so long as they are not constrained by rock, ice, and loss of habitat near the mountaintops (Maggini et al 2011, Elsen and Tingley 2015, Scridel et al 2018. Populations of many mountain bird species have declined in Europe (Lehikoinen et al 2019a), yet some in North America have remained stable (Ray et al 2017). Reasons for the differing trends are unclear.…”

“…Birds in protected areas, where some of the research in North America occurred, may be more resilient to climate change. Bird species in protected areas have had lower extinction rates and higher colonization rates compared to unprotected areas (Ray et al 2017, Lehikoinen et al 2019b, Peach et al 2019. Overall, many questions remain about how changing climatic conditions will affect the status and trends of bird populations in many regions of the world.…”