Christmas Bird Count Research Articles

The Erosion of Seasonality in Avian Communities

ABSTRACTAimSeasonality governs species composition at a given place and time. However, the effects of climate and land‐use change can vary by season, altering species composition. These changes can lead to a loss of distinct seasonal community composition, representing a novel form of biotic homogenisation. We ask if breeding and winter bird communities are becoming more similar over time. If so, is homogenisation occurring more rapidly in winter than in the breeding season, and has the presence of individual species changed between seasons?LocationNortheastern United States.Time Period1989–2019.Major Taxa StudiedTwo hundred thirty‐eight bird species.MethodsWe use data from The National Audubon Society's Christmas Bird Count and the North American Breeding Bird Survey to test if winter and breeding bird communities have become more similar (homogenised). We evaluate this change using the Sørensen dissimilarity index, and its components of turnover (species replacement) and nestedness (a subset of a more species rich community) and describe the mechanism in which the seasonal winter and breeding bird communities are changing.ResultsWe found that winter and breeding bird communities are homogenising, driven by significant decrease in turnover and a marginal decrease nestedness. When viewing breeding and wintering communities separately, we observe different trends. Breeding communities are becoming more unique with decreasing turnover and nestedness. Winter communities are becoming more similar to each other, with decreasing turnover and nestedness. More breeding species are declining and species that are typically found in the winter and year‐round residents are the main contributors to the homogenisation between seasons.Main ConclusionsWe show for the first time homogenisation between winter and breeding bird communities over time across the northeastern United States. This insight into how individual species are faring between seasons, and how they impact community structure, can be used when implementing conservation measures for maintaining ecological functioning and integrity.

Bayesian integrated species distribution models for hierarchical resource selection by a soaring bird

Migratory birds exhibit seasonal geographic range (hereafter, range) dynamics during the annual cycle. Few studies have examined how migratory birds select their habitats for range occupancy at the species level and space use at the individual level simultaneously. We hypothesized that environmental variables directly related to fitness components would affect the range occupancy probabilities of migrants, whereas environment variables related to movements and flights would affect the space use intensities of migrants. We built Bayesian integrated species distribution models (ISDMs) to evaluate the effects of climate conditions, wind conditions, and landcover compositions on the seasonal range dynamics of American white pelicans Pelecanus erythrorhynchos (hereafter, pelican) during summer and winter. The ISDMs estimated the summer range occupancy probabilities of pelicans with Breeding Bird Survey data, winter range occupancy probabilities with Christmas Bird Count data, and summer and winter space-use intensity rates with eBird data jointly. We evaluated the predictive performance of ISDMs using independent datasets of pelican GPS locations. Integrated species distribution models outperformed the occupancy-only models in the predictive performance of occupancy probabilities. Climate conditions had opposite effects on the range occupancy probabilities between the breeding and non-breeding grounds, whereas landcovers had relatively consistent effects on range occupancy probabilities between the seasons.

Population Trends of the Ferruginous Hawk (Buteo regalis) Wintering in California

Abstract The Ferruginous Hawk (Buteo regalis) is a raptor of conservation concern in much of its range. Population trend estimates from Breeding Bird Surveys and migration counts for this species are often contradictory and of low credibility. Therefore, we used Christmas Bird Count data to assess population trends for Ferruginous Hawks that winter in California, USA. Evidence suggests that the birds breeding in southeastern Washington and northeastern Oregon may represent a metapopulation that winters almost exclusively in California. Data for the 25-yr period from Count Year 98 (winter 1997–1998) to Count Year 122 (winter 2021–2022) from 22 California Christmas Bird Count circles in the core winter range of Ferruginous Hawks showed a significant positive trend. This positive trend contrasts with the continent-wide negative trends observed for most grassland/open country bird species and is surprising given ongoing declines of this species’ preferred winter habitat in California during this same period. We discuss potential explanations that may account for these differences, including the possibility that the California-wintering Ferruginous Hawks include a large proportion of birds breeding outside of southeastern Washington and northeastern Oregon.

Christmas Bird Count data are a reliable harvest-independent index for Ruffed Grouse monitoring in the eastern United States

Abstract Using data from the mid-1990s to the present, we assessed correlations of Ruffed Grouse (Bonasa umbellus) hunter cooperator reports from seven states to Breeding Bird Survey, Christmas Bird Count, and eBird data to determine which program’s trends best reflected patterns seen in hunter-sourced data that has historically been used for monitoring purposes. Christmas Bird Count data most closely reflected state-wide long-term trends in cooperator flush rates. Using an analytical approach that accounts for sources of bias and examines abundance at a finer spatial scale, we observed a pattern of decline across our study area. In recent decades, Ruffed Grouse populations in the eastern United States are thought to have suffered persistent declines due to a combination of young forest habitat loss and West Nile virus mortality. Declining hunter participation in much of the species’ range has highlighted the need to identify harvest-independent indices of grouse abundance to enable continued monitoring of regional long-term trends. Recent analytical methods can better capture complex trends in population dynamics, account for biases inherent to community-sourced data, and potentially inform designs of future survey efforts aimed at fulfilling priority monitoring and research needs. Comparable results across varying statistical methodologies suggest that our inferences are robust, demonstrating that Christmas Bird Count data can be used to inform regional monitoring efforts for grouse and other cryptic game bird populations, but require careful consideration of program designs and protocols to identify and implement data appropriately.

Quantifying the Effects of Energy Infrastructure on Bird Populations and Biodiversity.

Shale oil and gas production and wind energy generation both expanded rapidly across the United States between 2000 and 2020, raising concerns over impacts on wildlife. I combine longitudinal microdata from the National Audubon Society's Christmas Bird Count with geolocated registries of all wind turbines and shale wells constructed in the contiguous U.S. during this period to estimate the causal effects of these contrasting types of energy infrastructure on bird populations and biodiversity, which are key bellwethers of ecosystem health. Results show that the onset of shale oil and gas production reduces subsequent bird population counts by 15%, even after adjusting for location and year fixed effects, weather, counting effort, and land-use changes. Wind turbines do not have any measurable impact on bird counts. Negative effects of shale are larger when wells are drilled within important bird habitats.

Spatially explicit Bayesian hierarchical models improve estimates of avian population status and trends

Abstract Population trend estimates form the core of avian conservation assessments in North America and indicate important changes in the state of the natural world. The models used to estimate these trends would be more efficient and informative for conservation if they explicitly considered the spatial locations of the monitoring data. We created spatially explicit versions of some standard status and trend models applied to long-term monitoring data for birds across North America. We compared the spatial models to simpler non-spatial versions of the same models, fitting them to simulated data and real data from 3 broad-scale monitoring programs: the North American Breeding Bird Survey (BBS), the Christmas Bird Count, and a collection of programs we refer to as Migrating Shorebird Surveys. All the models generally reproduced the simulated trends and population trajectories when there were many data, and the spatial models performed better when there were fewer data and in locations where the local trends differed from the range-wide means. When fit to real data, the spatial models revealed interesting spatial patterns in trend, such as recent population increases along the Appalachian Mountains for the Eastern Whip-poor-will (Antrostomus vociferus), that were much less apparent in results from the non-spatial versions. The spatial models also had higher out-of-sample predictive accuracy than the non-spatial models for a selection of species using BBS data. The spatially explicit sharing of information allows fitting the models with much smaller strata, allowing for finer-grained patterns in trends. Spatially informed trends will facilitate more locally relevant conservation, highlight areas of conservation successes and challenges, and help generate and test hypotheses about the spatially dependent drivers of population change.

81st Annual Saskatchewan Christmas Bird Count - 2022

81st Annual Saskatchewan Christmas Bird Count - 2022

81st Annual Saskatchewan Christmas Bird Count - 2022

81st Annual Saskatchewan Christmas Bird Count - 2022

Winter range shifts and their associations with species traits are heterogeneous in eastern North American birds

Abstract Many species’ distributions are shifting in response to climate change. Many distributional shifts are predictably poleward or higher in elevation, but heterogeneity in the rate and direction of shifts both within and between species appears to be common. We found high heterogeneity in the trajectory of winter range shifts for 65 species of birds across eastern North America and in the different traits and trait interactions associated with these shifts across the spatial scales we examined. We used data from the Christmas Bird Count to quantify the trajectory of winter latitudinal center of abundance range shifts over 4 decades (1980–2019) for 65 species of songbirds and woodpeckers in North America, both across eastern North America (ENA) as a whole and for the Atlantic (ATL) and Mississippi (MISS) flyways separately. We then used linear models and Akaike’s Information Criterion with small-sample size correction (AICc) model selection to test whether species traits could explain variation in range shifts or flyway discrepancies. Across ENA, most species showed northward latitudinal range shifts, but some showed no latitudinal shift while others shifted southwards. Amongst ATL and MISS, we documented both within- and between-species differences in the rate and direction of latitudinal shifts, complicating the results from across ENA. No single trait emerged as a dominant driver of range shift differences at the ENA and flyway scales. Migration strategy interacted with insectivory to explain variation at the largest spatial scale (ENA), whereas frugivory and mean winter latitude explained much of the variation in ATL and MISS, respectively. Exploring heterogeneity in range shifts within and between species, and in the associations between range shifts and life history traits, will help us better understand the mechanisms that mediate differing responses to environmental change and predict which species will be better able to adapt to those changes.

Evidence of Continuing Downward Trends in American Kestrel Populations and Recommendations for Research into Causal Factors

ABSTRACT We analyzed long-term datasets from nest box programs, Breeding Bird Surveys run by the US Geological Survey, Christmas Bird Counts run by the National Audubon Society, and counts from two key fall migration watch sites, Hawk Mountain Sanctuary and Cape May Hawkwatch. We found that populations of American Kestrels (Falco sparverius) in North America are generally still declining, albeit with some caveats. Some populations are actually increasing, while others are remaining stable. Overall, the magnitude of annual change appears to be decreasing slightly during recent years. To understand potential causes of the decline, we recommend the following courses of action in no particular order: (1) determine whether the increase in Cooper's Hawk (Accipiter cooperii) populations is restricting kestrel distributions by the mere presence of the larger raptor; (2) study the effects of habitat loss and/or degradation on the falcon's wintering range; (3) further investigate on a broader spatial scale whether within-season habitat alterations are creating ecological traps for breeding kestrels; (4) determine the importance of arthropods in the diet of kestrels, especially the long-term population trends and timing of emergence of grasshoppers in relation to kestrel breeding chronology; (5) discover whether rodenticides pose a serious risk to American Kestrels across North America; (6) learn more about possible effects, both direct and indirect, that the use of neonicotinoids may have on kestrels; and (7) continue ongoing studies of the effect of climate change on these birds.

Poleward shifts and altered periodicity in boreal bird irruptions over six decades.

Range boundaries are long-term biogeographic features of species distributions and abundance. However, many species demonstrate dynamic range boundaries, reflecting strong seasonal and annual variability in migratory behaviour. As a form of facultative migration, irruptions involve the movement of many individuals outside of their resident range in response to climate variability, resource availability, and demographic processes. Many species have experienced range shifts and altered phenology in response to modern climate change, but spatiotemporal changes in irruption dynamics are less well known. We quantified changes in the geography and periodicity of boreal bird irruptions across eastern North America from 1960 to 2021. Using data from Audubon's Christmas Bird Count for nine finch species, including several exhibiting recent population declines, we evaluated latitudinal trends in southern range and irruption boundaries and characterized irruption periodicity using spectral wavelet analysis. Six boreal birds exhibited significant northward shifts in their southern range boundaries and three species displayed shifts in their southern irruption boundaries. Irruption periodicity across multiple species was consistent across the 1960s and 1970s, culminating in frequent and synchronized irruptions of multiple species (superflights) during earlier decades. Coherence between species dampened beginning in the early 1980s as superflight periodicity became increasingly unstructured, finally reforming in recent decades, after 2000. Boreal birds are considered important sentinels of the boreal forests, and northward shifts and altered periodicity of irruptions may indicate broad-scale changes in climate- and resource-associated drivers operating across the boreal forests.

Spatial and temporal non-stationarity in long-term population dynamics of over-wintering birds of North America.

Understanding population changes across long time scales and at fine spatiotemporal resolutions is important for confronting a broad suite of conservation challenges. However, this task is hampered by a lack of quality long-term census data for multiple species collected across large geographic regions. Here, we used century-long (1919-2018) data from the Audubon Christmas Bird Count (CBC) survey to assess population changes in over 300 avian species in North America and evaluate their temporal non-stationarity. To estimate population sizes across the entire century, we employed a Bayesian hierarchical model that accounts for species detection probabilities, variable sampling effort, and missing data. We evaluated population trends using generalized additive models (GAMs) and assessed temporal non-stationarity in the rate of population change by extracting the first derivatives from the fitted GAM functions. We then summarized the population dynamics across species, space, and time using a non-parametric clustering algorithm that categorized individual population trends into four distinct trend clusters. We found that species varied widely in their population trajectories, with over 90% of species showing a considerable degree of spatial and/or temporal non-stationarity, and many showing strong shifts in the direction and magnitude of population trends throughout the past century. Species were roughly equally distributed across the four clusters of population trajectories, although grassland, forest, and desert specialists more commonly showed declining trends. Interestingly, for many species, region-wide population trends often differed from those observed at individual sites, suggesting that conservation decisions need to be tailored to fine spatial scales. Together, our results highlight the importance of considering spatial and temporal non-stationarity when assessing long-term population changes. More generally, we demonstrate the promise of novel statistical techniques for improving the utility and extending the temporal scope of existing citizen science datasets.

Thirty Years of Migration and Winter Count Data Indicate Regional Differences in Population Trajectories for American Kestrels in North America

ABSTRACT Using fall migration trend data from the Raptor Population Index analyses (n = 59 count sites) paired with winter Christmas Bird Count trend data at the USA state and Canadian province level, we evaluated continental and regional patterns in trends of American Kestrels (Falco sparverius) over the last 30 yr. Long-term trends at the continental and regional level showed widespread declines in the number of kestrels counted during both fall migration and winter. The lone exception was in western North America where declining migration counts were evident, but could at least partly be explained by increasing winter counts. These results suggest that western kestrels are shifting migratory tendencies, migrating shorter distances (short-stopping), or are not migrating at all. This contrasts with patterns in central and eastern North America where kestrel counts declined in both fall and winter over the last 20- and 30-yr periods. Recent trends (2009–2019) showed less widespread declines in both fall and winter across North America and for most regions, suggesting kestrel declines might have moderated in the past decade. However, the species remains at significantly reduced abundance levels compared to the recent past and has not rebounded.

Long-term Christmas Bird Counts describe neotropical urban bird diversity.

A significant gap in understanding the response of biodiversity to urban areas is the lack of long-term studies. Most of the information on urban birds comes from studies carried out in the northern hemisphere, and they include data that don´t exceed three years. Although short-term studies contribute to knowledge about bird community diversity and their spatial distribution in urban areas, they could be biased towards more conspicuous species. One of the few multi-temporal datasets available for birds in urban areas is the Christmas Bird Count (CBC). Using annual CBC data available between 2001 and 2018 from 21 urban and peri-urban sample sites assessed from the main cities of Colombia, we identified and analyzed long-term trends on the cumulative diversity of bird communities as well as on their spatial distribution. We estimated comparative trends in richness, number of individuals counted, similarity, and complementarity of avifauna for each city and sample site based on their responses to urbanization and dietary guilds. We identified almost a quarter of the species registered in Colombia (464 of 1954). The representativeness of the community obtained for 18 years exceeds 84%, showing richness that ranges between 214 and 278 species in the three cities. Bird species and individuals registered showed wide variation of the sample sites. We found more dwellers, insectivorous and granivorous species in urban areas, with frugivores relegated to peri-urban sites, usually coinciding with avoider species. Natural peri-urban areas and intra-urban wetlands and urban parks were the most important refuges for birds and maintained the highest avoider and utilizer species richness. Long-term inventories are fundamental for determining consolidated bird diversity and distributional patterns. This information established a baseline for decision-making and applying recommendations that allow reconciling the growing demand for urban areas with the need to preserve the native avifauna in megadiverse Neotropical countries such as Colombia.

Acadia National Park Winter Birds: 51 Years of Change along the Coast of Maine

There is a long history of recording bird observation in Acadia National Park, ME. These studies and resulting long-term data sets provide evidence of changes happening within and around the park, as well as an opportunity to compare local dynamics with trends detected in regional to continental-scale studies. Over 51 years (1971–2021), community volunteers in and around Acadia National Park engaged in annual Christmas bird counts (CBC), collecting valuable information to assess winter bird-population dynamics and species trends. We analyzed the cumulative data from 2 CBC circles that encompass Acadia and the surrounding lands and waters to generate a combined summary of early winter population-trend estimates for 162 species. We found a 43% reduction in the total number of birds over the 51-year study, with 42 species exhibiting declines, and 33 species showing increasing abundance. The annual number of species observed has declined by over 7%; however, the cumulative species in the full dataset continues to increase as newly observed species are added in most years. Our study complements many other studies from Acadia documenting ongoing changes in the physical environment and coastal biota. Conservation and management actions take place at the local level (e.g., Acadia National Park), and local resource data and trends are critical to synthesize and share for effective decision making.

Composite population trends reveal status of wintering diurnal raptors in the Northwestern USA

Integrated models can combine data from disparate monitoring programs to improve inference into population dynamics because trends in disparate datasets can be interpreted using a single index. We present a composite index of raptor population trends that combines data from two monitoring programs into a single estimate. The National Audubon Society's Christmas Bird Count and the East Cascade Audubon Society's Winter Raptor Survey use different methods to monitor the same populations of wintering raptors. Observers record all birds detected within 452 km2 ‘circles’ during the Christmas Bird Count, and during the Winter Raptor Survey observers count raptors along roadways. We present the results of a joint likelihood model that combines trends of raptors counted during both programs into a single population trend from 2005 to 2020. Population indices of the Bald Eagle (Haliaeetus leucocephalus), Ferruginous Hawk (Buteo regalis), Cooper's Hawk (Accipiter cooperii), Red-shouldered Hawk (Buteo lineatus), and Red-tailed Hawk (Buteo jamaicensis) increased over the course of our study, whereas Prairie Falcon (Falco mexicanus) and White-tailed Kite (Elanus leucurus) population indices declined. Further, the composite index for White-tailed Kite declined at a rate of 22 % (80 % CRI = 17 %–28 %) per year—supporting evidence of declines from breeding season surveys. We recommend further research into population trends of this species within its core California range. Our study advances efforts to combine trends in datasets collected using differing methodologies to estimate large-scale population trends from disparate data sets.

Migratory Movements and Home Ranges of Geographically Distinct Wintering Populations of a Soaring Bird

Migratory soaring birds exhibit spatiotemporal variation in their circannual movements. Nevertheless, it remains uncertain how different winter environments affect the circannual movement patterns of migratory soaring birds. Here, we investigated annual movement strategies of American white pelicans Pelecanus erythrorhynchos (hereafter, pelican) from two geographically distinct wintering grounds in the Southern and Northern Gulf of Mexico (GOM). We hypothesized that hourly movement distance and home range size of a soaring bird would differ between different geographic regions because of different thermals and wind conditions and resource availability. We calculated average and maximum hourly movement distances and seasonal home ranges of GPS-tracking pelicans. We then evaluated the effects of hour of the day, seasons, two wintering regions in the Southern and Northern GOM, human footprint index, and relative pelican abundance from Christmas Bird Count data on pelican hourly movement distances and seasonal home ranges using linear mixed models and generalized linear mixed models. American white pelicans moved at greatest hourly distance near 1200 h at breeding grounds and during spring and autumn migrations. Both wintering populations in the Northern and Southern GOM exhibited similar hourly movement distances and seasonal home ranges at the shared breeding grounds and during spring and autumn migrations. However, pelicans wintering in the Southern GOM showed shorter hourly movement distances and smaller seasonal home ranges than those in the Northern GOM. Hourly movement distances and home ranges of pelicans increased with increasing human footprint index. Winter hourly movements and home ranges of pelicans differed between the Northern and Southern GOM; however, the winter difference in pelican movements did not carry over to the shared breeding grounds during summers. Therefore, exogenous factors may be the primary drivers to shape the flying patterns of migratory soaring birds.

Assessing long‐term dynamics of non‐breeding Brown Pelican (Pelecanus occidentalis) populations using Christmas Bird Count data

Brown PelicanPelecanus occidentalispopulations are recovering in many parts of their geographical range in coastal areas of North and Central America following near‐decimation in the mid‐20th century. However, populations have exhibited varying recovery rates that could be rectified with improved understanding of influencing factors, including population stressors, particularly during the non‐breeding period. Brown Pelicans are central‐place foragers and sensitive to changes in surface fish distributions that may result from stochastic events such as the El Niño Southern Oscillation. We used 34 years of Audubon Christmas Bird Count (CBC) data (1984–2017) to evaluate long‐term density‐dependent and density‐independent population dynamics of Brown Pelican populations in coastal areas of Alabama, California, Louisiana and Mississippi. We used exploratory dynamic factor analysis across four population time series to model a linear combination of common trends from CBC data. We then developed a suite of state space models to assess effects of density‐dependent and density‐independent factors (e.g. Southern Oscillation Index) on Pelican populations dynamics over time. Generally, Brown Pelican populations increased substantially following recovery efforts in the mid‐1980s, but have stabilized and fluctuated over time, represented by three latent trends. Populations generally were subject to density‐dependent regulatory mechanisms, with only the Louisiana population exhibiting a significant negative association with the fall/winter Southern Oscillation Index from 2 years earlier. Improved understanding of underlying regulatory mechanisms driving or hindering Brown Pelican population recovery may help in targeting regional or sub‐regional conservation measures, particularly during lesser‐known periods of their annual cycle.

80th Annual Saskatchewan Christmas Bird Count - 2021

80th Annual Saskatchewan Christmas Bird Count - 2021

The Citizen Science Paradox

Citizen science (CS) is now very popular in ecology. The number of scientific publications referencing CS has increased steadily over the past 15 years, with more than 1150 publications today. However, the multiplicity of research involved suggests that this number is highly underestimated. Based on this paradox, a literature review on CS shows that while its formalization in 2009 facilitated its referencing, about 70% of the publications are not referenced using CS as keyword. To understand this under-representation, an analysis of 149 publications related to the famous Christmas Bird Count program shows that this underestimation is not mainly related to the diversity of keywords used to describe CS, but rather to the fact that CS is mainly considered as a method (four publications out of five). The results also show that taking into account the whole text of a publication would represent a substantial improvement for the analysis of scientific databases, whatever the field of research.