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Change Points in the Population Trends of Aerial-Insectivorous Birds in North America: Synchronized in Time across Species and Regions.

Smith AC, Hudson MA, Downes CM, Francis CM - PLoS ONE (2015)

Bottom Line: We found evidence for group-level change points in 85% of the strata.This group-level synchrony in AI population trends is likely evidence of a response to a common environmental factor(s) with similar effects on many species across broad spatial extents.The timing and geographic patterns of the change points that we identify here should provide a spring-board for research into the causes behind aerial insectivore declines.

View Article: PubMed Central - PubMed

Affiliation: Canadian Wildlife Service, Environment Canada, Ottawa, Ontario, Canada.

ABSTRACT
North American populations of aerial insectivorous birds are in steep decline. Aerial insectivores (AI) are a group of bird species that feed almost exclusively on insects in flight, and include swallows, swifts, nightjars, and flycatchers. The causes of the declines are not well understood. Indeed, it is not clear when the declines began, or whether the declines are shared across all species in the group (e.g., caused by changes in flying insect populations) or specific to each species (e.g., caused by changes in species' breeding habitat). A recent study suggested that population trends of aerial insectivores changed for the worse in the 1980s. If there was such a change point in trends of the group, understanding its timing and geographic pattern could help identify potential causes of the decline. We used a hierarchical Bayesian, penalized regression spline, change point model to estimate group-level change points in the trends of 22 species of AI, across 153 geographic strata of North America. We found evidence for group-level change points in 85% of the strata. Change points for flycatchers (FC) were distinct from those for swallows, swifts and nightjars (SSN) across North America, except in the Northeast, where all AI shared the same group-level change points. During the 1980s, there was a negative change point across most of North America, in the trends of SSN. For FC, the group-level change points were more geographically variable, and in many regions there were two: a positive change point followed by a negative change point. This group-level synchrony in AI population trends is likely evidence of a response to a common environmental factor(s) with similar effects on many species across broad spatial extents. The timing and geographic patterns of the change points that we identify here should provide a spring-board for research into the causes behind aerial insectivore declines.

No MeSH data available.


Related in: MedlinePlus

Examples of Simultaneously Estimated, Species-Specific (Blue Triangles) and Group-Level (Black and Grey Triangles) Change Points, for a Selection of Species and Regions.Triangles pointing up represent positive change points, while triangles pointing down represent negative change points. Many species’ trajectories follow the group trajectory relatively well for part of the time series, but then diverge following a species-specific change point: Chimney Swift in the Indiana portion of Bird Conservation Region (BCR) 24 (A), and Great Crested Flycatcher in the Maryland portion of BCR 30 (B). Many other species trajectories include only the group-level change points: Great Crested Flycatcher in the New York portion of BCR 13 (C). In a few cases the species-specific change points contradict the group-level change points: Eastern Phoebe in the Quebec portion of BCR 14 (D). Region names relate to analytical strata, which are defined by the intersections of states and provinces with BCRs. BCR names are: BCR 13, Lower Great Lakes / St. Lawrence Plain; BCR 14, Atlantic Northern Forest; BCR 24, Central Hardwoods; and BCR 30, New England/Mid-Atlantic Coast.
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pone.0130768.g007: Examples of Simultaneously Estimated, Species-Specific (Blue Triangles) and Group-Level (Black and Grey Triangles) Change Points, for a Selection of Species and Regions.Triangles pointing up represent positive change points, while triangles pointing down represent negative change points. Many species’ trajectories follow the group trajectory relatively well for part of the time series, but then diverge following a species-specific change point: Chimney Swift in the Indiana portion of Bird Conservation Region (BCR) 24 (A), and Great Crested Flycatcher in the Maryland portion of BCR 30 (B). Many other species trajectories include only the group-level change points: Great Crested Flycatcher in the New York portion of BCR 13 (C). In a few cases the species-specific change points contradict the group-level change points: Eastern Phoebe in the Quebec portion of BCR 14 (D). Region names relate to analytical strata, which are defined by the intersections of states and provinces with BCRs. BCR names are: BCR 13, Lower Great Lakes / St. Lawrence Plain; BCR 14, Atlantic Northern Forest; BCR 24, Central Hardwoods; and BCR 30, New England/Mid-Atlantic Coast.

Mentions: In addition to the group-level change points that we have focused on here, we also identified species-specific change points. For all species included in our analyses, except Eastern Whip-poor-will, species-specific change points were identified in at least one stratum (Table 1). Species varied in the number and direction of these species-specific change points. For example, Western Wood-Pewee, Acadian Flycatcher, and the Northern Rough-winged Swallow had species-specific change points in relatively few of the strata where they were included (Table 1). By contrast, Chimney Swift, Eastern Phoebe, Tree Swallow, Olive-sided Flycatcher, and Barns Swallow had species-specific change points in many (up to 89% of the strata where they were included, Table 1). In almost all cases, the species-specific change points represented change points that followed or pre-dated the group-level change points (Fig 7A and 7C). However, for Eastern Phoebe, there was a positive species-specific change point that directly contradicted the group-level negative change point that occurred in Eastern North America (Fig 7D, Table 1). We have provided a table detailing the timing of positive and negative species-specific change points, for all species included here (22 species across 153 strata), in S2 Table to enable further study by researchers and managers interested in single species of AI.


Change Points in the Population Trends of Aerial-Insectivorous Birds in North America: Synchronized in Time across Species and Regions.

Smith AC, Hudson MA, Downes CM, Francis CM - PLoS ONE (2015)

Examples of Simultaneously Estimated, Species-Specific (Blue Triangles) and Group-Level (Black and Grey Triangles) Change Points, for a Selection of Species and Regions.Triangles pointing up represent positive change points, while triangles pointing down represent negative change points. Many species’ trajectories follow the group trajectory relatively well for part of the time series, but then diverge following a species-specific change point: Chimney Swift in the Indiana portion of Bird Conservation Region (BCR) 24 (A), and Great Crested Flycatcher in the Maryland portion of BCR 30 (B). Many other species trajectories include only the group-level change points: Great Crested Flycatcher in the New York portion of BCR 13 (C). In a few cases the species-specific change points contradict the group-level change points: Eastern Phoebe in the Quebec portion of BCR 14 (D). Region names relate to analytical strata, which are defined by the intersections of states and provinces with BCRs. BCR names are: BCR 13, Lower Great Lakes / St. Lawrence Plain; BCR 14, Atlantic Northern Forest; BCR 24, Central Hardwoods; and BCR 30, New England/Mid-Atlantic Coast.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493114&req=5

pone.0130768.g007: Examples of Simultaneously Estimated, Species-Specific (Blue Triangles) and Group-Level (Black and Grey Triangles) Change Points, for a Selection of Species and Regions.Triangles pointing up represent positive change points, while triangles pointing down represent negative change points. Many species’ trajectories follow the group trajectory relatively well for part of the time series, but then diverge following a species-specific change point: Chimney Swift in the Indiana portion of Bird Conservation Region (BCR) 24 (A), and Great Crested Flycatcher in the Maryland portion of BCR 30 (B). Many other species trajectories include only the group-level change points: Great Crested Flycatcher in the New York portion of BCR 13 (C). In a few cases the species-specific change points contradict the group-level change points: Eastern Phoebe in the Quebec portion of BCR 14 (D). Region names relate to analytical strata, which are defined by the intersections of states and provinces with BCRs. BCR names are: BCR 13, Lower Great Lakes / St. Lawrence Plain; BCR 14, Atlantic Northern Forest; BCR 24, Central Hardwoods; and BCR 30, New England/Mid-Atlantic Coast.
Mentions: In addition to the group-level change points that we have focused on here, we also identified species-specific change points. For all species included in our analyses, except Eastern Whip-poor-will, species-specific change points were identified in at least one stratum (Table 1). Species varied in the number and direction of these species-specific change points. For example, Western Wood-Pewee, Acadian Flycatcher, and the Northern Rough-winged Swallow had species-specific change points in relatively few of the strata where they were included (Table 1). By contrast, Chimney Swift, Eastern Phoebe, Tree Swallow, Olive-sided Flycatcher, and Barns Swallow had species-specific change points in many (up to 89% of the strata where they were included, Table 1). In almost all cases, the species-specific change points represented change points that followed or pre-dated the group-level change points (Fig 7A and 7C). However, for Eastern Phoebe, there was a positive species-specific change point that directly contradicted the group-level negative change point that occurred in Eastern North America (Fig 7D, Table 1). We have provided a table detailing the timing of positive and negative species-specific change points, for all species included here (22 species across 153 strata), in S2 Table to enable further study by researchers and managers interested in single species of AI.

Bottom Line: We found evidence for group-level change points in 85% of the strata.This group-level synchrony in AI population trends is likely evidence of a response to a common environmental factor(s) with similar effects on many species across broad spatial extents.The timing and geographic patterns of the change points that we identify here should provide a spring-board for research into the causes behind aerial insectivore declines.

View Article: PubMed Central - PubMed

Affiliation: Canadian Wildlife Service, Environment Canada, Ottawa, Ontario, Canada.

ABSTRACT
North American populations of aerial insectivorous birds are in steep decline. Aerial insectivores (AI) are a group of bird species that feed almost exclusively on insects in flight, and include swallows, swifts, nightjars, and flycatchers. The causes of the declines are not well understood. Indeed, it is not clear when the declines began, or whether the declines are shared across all species in the group (e.g., caused by changes in flying insect populations) or specific to each species (e.g., caused by changes in species' breeding habitat). A recent study suggested that population trends of aerial insectivores changed for the worse in the 1980s. If there was such a change point in trends of the group, understanding its timing and geographic pattern could help identify potential causes of the decline. We used a hierarchical Bayesian, penalized regression spline, change point model to estimate group-level change points in the trends of 22 species of AI, across 153 geographic strata of North America. We found evidence for group-level change points in 85% of the strata. Change points for flycatchers (FC) were distinct from those for swallows, swifts and nightjars (SSN) across North America, except in the Northeast, where all AI shared the same group-level change points. During the 1980s, there was a negative change point across most of North America, in the trends of SSN. For FC, the group-level change points were more geographically variable, and in many regions there were two: a positive change point followed by a negative change point. This group-level synchrony in AI population trends is likely evidence of a response to a common environmental factor(s) with similar effects on many species across broad spatial extents. The timing and geographic patterns of the change points that we identify here should provide a spring-board for research into the causes behind aerial insectivore declines.

No MeSH data available.


Related in: MedlinePlus