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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

Timing of Well-Supported, Negative (A) and Positive (B) Change Points in Population Trends that are Shared across North American Swallows, Swifts, and Nightjars.Timings were estimated separately within each of the geographic strata; strata are coloured based on the year that had the highest posterior probability of including a change point. The plots below the maps show the years with highest probability (points) as well as adjacent years that also had relatively high posterior probability of including the change point (error bars, years with posterior:prior odds ratio > 3). In the plots, the strata are sorted from west to east based on the longitude of their centroid, and coloured regions reflect the decadal colours used in the maps. Strata coloured grey were not modeled due to insufficient data. Strata in white had no well-supported change points (either positive or negative).
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pone.0130768.g003: Timing of Well-Supported, Negative (A) and Positive (B) Change Points in Population Trends that are Shared across North American Swallows, Swifts, and Nightjars.Timings were estimated separately within each of the geographic strata; strata are coloured based on the year that had the highest posterior probability of including a change point. The plots below the maps show the years with highest probability (points) as well as adjacent years that also had relatively high posterior probability of including the change point (error bars, years with posterior:prior odds ratio > 3). In the plots, the strata are sorted from west to east based on the longitude of their centroid, and coloured regions reflect the decadal colours used in the maps. Strata coloured grey were not modeled due to insufficient data. Strata in white had no well-supported change points (either positive or negative).

Mentions: Across most of North America, swallows, swifts, and nightjar population trends showed a common, well-supported negative change point during the 1980’s (Fig 3A). There were a few strata where the data supported a positive change point in SSN trends. The majority of these (few) positive change points were in eastern North America; in almost all cases, they occurred a few years prior to the negative change point (Fig 3B). Overall, SSN trajectories appeared very similar across the continent due to the single negative change point that was consistent across most strata. However, the magnitude and direction of the group trends, (i.e., the slopes before and after the common change point) showed some geographic variation. In the west and northeast, the trends were initially moderately positive or stable, followed by a relatively steep decline through to the present (orange trajectories in Fig 4). In the south, many trajectories began with a period of steep increase, followed by a decreasing or stable trajectory through to the present (Fig 4). This geographic pattern in the trends before and after the change points resulted in some geographic variation in the overall trend among strata (greater overall decline in the northeast and less overall decline in the south), even though the timing and direction of the change point was consistent across the strata.


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)

Timing of Well-Supported, Negative (A) and Positive (B) Change Points in Population Trends that are Shared across North American Swallows, Swifts, and Nightjars.Timings were estimated separately within each of the geographic strata; strata are coloured based on the year that had the highest posterior probability of including a change point. The plots below the maps show the years with highest probability (points) as well as adjacent years that also had relatively high posterior probability of including the change point (error bars, years with posterior:prior odds ratio > 3). In the plots, the strata are sorted from west to east based on the longitude of their centroid, and coloured regions reflect the decadal colours used in the maps. Strata coloured grey were not modeled due to insufficient data. Strata in white had no well-supported change points (either positive or negative).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130768.g003: Timing of Well-Supported, Negative (A) and Positive (B) Change Points in Population Trends that are Shared across North American Swallows, Swifts, and Nightjars.Timings were estimated separately within each of the geographic strata; strata are coloured based on the year that had the highest posterior probability of including a change point. The plots below the maps show the years with highest probability (points) as well as adjacent years that also had relatively high posterior probability of including the change point (error bars, years with posterior:prior odds ratio > 3). In the plots, the strata are sorted from west to east based on the longitude of their centroid, and coloured regions reflect the decadal colours used in the maps. Strata coloured grey were not modeled due to insufficient data. Strata in white had no well-supported change points (either positive or negative).
Mentions: Across most of North America, swallows, swifts, and nightjar population trends showed a common, well-supported negative change point during the 1980’s (Fig 3A). There were a few strata where the data supported a positive change point in SSN trends. The majority of these (few) positive change points were in eastern North America; in almost all cases, they occurred a few years prior to the negative change point (Fig 3B). Overall, SSN trajectories appeared very similar across the continent due to the single negative change point that was consistent across most strata. However, the magnitude and direction of the group trends, (i.e., the slopes before and after the common change point) showed some geographic variation. In the west and northeast, the trends were initially moderately positive or stable, followed by a relatively steep decline through to the present (orange trajectories in Fig 4). In the south, many trajectories began with a period of steep increase, followed by a decreasing or stable trajectory through to the present (Fig 4). This geographic pattern in the trends before and after the change points resulted in some geographic variation in the overall trend among strata (greater overall decline in the northeast and less overall decline in the south), even though the timing and direction of the change point was consistent across the strata.

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