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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 Group-Level, Negative (A) and positive (B) Change Points in Population Trends that are Shared across North American Flycatcher Populations.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 (neither positive nor negative).
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pone.0130768.g005: Timing of Well-Supported Group-Level, Negative (A) and positive (B) Change Points in Population Trends that are Shared across North American Flycatcher Populations.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 (neither positive nor negative).

Mentions: Flycatcher population trajectories showed common, well-supported negative change points in many strata across North America, but the timing of these downturns varied geographically (Fig 5A). In general, the negative change points occurred in the late 1970s in parts of the lower American Midwest, Kentucky, and Tennessee; in the mid-1980s in the northeastern US, parts of Texas, Georgia and South Carolina, and eastern Canada (with the exception of Nova Scotia); in late 1980s and early 1990s in much of the rest of Canada, north-central US, and parts of Texas and Alabama; and in the 2000s in the western US, western British Columbia, and Alaska. Flycatcher population trajectories in many strata also showed consistent positive change points that were strongly geographically separated: occurring either in the 1970s in eastern North America, or approximately in 2000 in western North America (Fig 5B). In the west, FC trajectories were characterized by a steep, long-term decline from the start of the time series (1970), followed by a positive change point in the late 1990s or early 2000s, a period of population increase, and finally a negative change point and decrease starting approximately in 2009 (Fig 4). In the southeast, FC trajectories were broadly similar to trajectories in the northeast for the early part of the time series, but in most strata, the only clear change in trend was an early, positive change point that moderated the previously steep rate of decline (Fig 4).


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 Group-Level, Negative (A) and positive (B) Change Points in Population Trends that are Shared across North American Flycatcher Populations.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 (neither positive nor negative).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130768.g005: Timing of Well-Supported Group-Level, Negative (A) and positive (B) Change Points in Population Trends that are Shared across North American Flycatcher Populations.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 (neither positive nor negative).
Mentions: Flycatcher population trajectories showed common, well-supported negative change points in many strata across North America, but the timing of these downturns varied geographically (Fig 5A). In general, the negative change points occurred in the late 1970s in parts of the lower American Midwest, Kentucky, and Tennessee; in the mid-1980s in the northeastern US, parts of Texas, Georgia and South Carolina, and eastern Canada (with the exception of Nova Scotia); in late 1980s and early 1990s in much of the rest of Canada, north-central US, and parts of Texas and Alabama; and in the 2000s in the western US, western British Columbia, and Alaska. Flycatcher population trajectories in many strata also showed consistent positive change points that were strongly geographically separated: occurring either in the 1970s in eastern North America, or approximately in 2000 in western North America (Fig 5B). In the west, FC trajectories were characterized by a steep, long-term decline from the start of the time series (1970), followed by a positive change point in the late 1990s or early 2000s, a period of population increase, and finally a negative change point and decrease starting approximately in 2009 (Fig 4). In the southeast, FC trajectories were broadly similar to trajectories in the northeast for the early part of the time series, but in most strata, the only clear change in trend was an early, positive change point that moderated the previously steep rate of decline (Fig 4).

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