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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

Group-level Trends for Flycatchers (FC) and for Swallows, Swifts, and Nightjars (SSN), Before and After Well-Supported, Group-Level Change Points.Group-level trends are defined as the average annual rates of change from the group-level trajectories of the piecewise linear regression spline model. The graph is divided into positive (A and C) and negative (B and D) change points for species of swallows, swifts, and nightjars (A and B), and flycatchers (C and D). Only one quadrant from each of the four plots is shown: the quadrant that included points representing all well-supported change points for a particular group and direction. The colours of the points indicate the decade in which the change point occurred and match previous figures (Figs 3 and 5). The size of the points reflects the posterior probability of the change point occurring at that time (i.e., larger points reflect change points with higher probability).
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pone.0130768.g006: Group-level Trends for Flycatchers (FC) and for Swallows, Swifts, and Nightjars (SSN), Before and After Well-Supported, Group-Level Change Points.Group-level trends are defined as the average annual rates of change from the group-level trajectories of the piecewise linear regression spline model. The graph is divided into positive (A and C) and negative (B and D) change points for species of swallows, swifts, and nightjars (A and B), and flycatchers (C and D). Only one quadrant from each of the four plots is shown: the quadrant that included points representing all well-supported change points for a particular group and direction. The colours of the points indicate the decade in which the change point occurred and match previous figures (Figs 3 and 5). The size of the points reflects the posterior probability of the change point occurring at that time (i.e., larger points reflect change points with higher probability).

Mentions: In the regions with well-supported positive change points for SSN, the group trends were all strongly negative before the change point and positive afterwards (Fig 6A). At the change point, the rate of population change increased by approximately 6%/year (from approximately 4%/year decline to 2%/year increase). In regions with well-supported negative change points for SSN, the group trends were positive, relatively stable, or slightly negative (between 1%/year decline and 3%/year increase) before the change point and were all negative following the change points (Fig 6B). At these negative change points, most of the trends decreased by approximately 2–4%/year, although a few decreased by much more.


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)

Group-level Trends for Flycatchers (FC) and for Swallows, Swifts, and Nightjars (SSN), Before and After Well-Supported, Group-Level Change Points.Group-level trends are defined as the average annual rates of change from the group-level trajectories of the piecewise linear regression spline model. The graph is divided into positive (A and C) and negative (B and D) change points for species of swallows, swifts, and nightjars (A and B), and flycatchers (C and D). Only one quadrant from each of the four plots is shown: the quadrant that included points representing all well-supported change points for a particular group and direction. The colours of the points indicate the decade in which the change point occurred and match previous figures (Figs 3 and 5). The size of the points reflects the posterior probability of the change point occurring at that time (i.e., larger points reflect change points with higher probability).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130768.g006: Group-level Trends for Flycatchers (FC) and for Swallows, Swifts, and Nightjars (SSN), Before and After Well-Supported, Group-Level Change Points.Group-level trends are defined as the average annual rates of change from the group-level trajectories of the piecewise linear regression spline model. The graph is divided into positive (A and C) and negative (B and D) change points for species of swallows, swifts, and nightjars (A and B), and flycatchers (C and D). Only one quadrant from each of the four plots is shown: the quadrant that included points representing all well-supported change points for a particular group and direction. The colours of the points indicate the decade in which the change point occurred and match previous figures (Figs 3 and 5). The size of the points reflects the posterior probability of the change point occurring at that time (i.e., larger points reflect change points with higher probability).
Mentions: In the regions with well-supported positive change points for SSN, the group trends were all strongly negative before the change point and positive afterwards (Fig 6A). At the change point, the rate of population change increased by approximately 6%/year (from approximately 4%/year decline to 2%/year increase). In regions with well-supported negative change points for SSN, the group trends were positive, relatively stable, or slightly negative (between 1%/year decline and 3%/year increase) before the change point and were all negative following the change points (Fig 6B). At these negative change points, most of the trends decreased by approximately 2–4%/year, although a few decreased by much more.

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