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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

Comparison of Annual Indices of Abundance from the BBS Generated by the Annual Index Model (Spatial CAR) and by the Trend Model Currently Used by Environment Canada’s Canadian Wildlife Service (CWS Trend).Examples include plots for Olive-sided Flycatcher in Ontario/Bird Conservation Region (BCR)12 (A), Tree Swallow in Ontario/BCR 13 (B), Olive-sided Flycatcher in Quebec/BCR 12 (C), and Tree Swallow in Alberta/BCR 6 (D). Species and regions represent examples where the two models give very similar estimates (e.g. A and B), or very different estimates (e.g., C and D). Region names relate to analytical strata, which are defined by the intersections of Canadian provinces with Bird Conservation Regions (BCRs, indexed here by their numbers). BCR names are: BCR 12, Boreal Hardwood Transition; BCR 13, Lower Great Lakes / St. Lawrence Plain; and BCR 6, Boreal Taiga Plains.
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pone.0130768.g001: Comparison of Annual Indices of Abundance from the BBS Generated by the Annual Index Model (Spatial CAR) and by the Trend Model Currently Used by Environment Canada’s Canadian Wildlife Service (CWS Trend).Examples include plots for Olive-sided Flycatcher in Ontario/Bird Conservation Region (BCR)12 (A), Tree Swallow in Ontario/BCR 13 (B), Olive-sided Flycatcher in Quebec/BCR 12 (C), and Tree Swallow in Alberta/BCR 6 (D). Species and regions represent examples where the two models give very similar estimates (e.g. A and B), or very different estimates (e.g., C and D). Region names relate to analytical strata, which are defined by the intersections of Canadian provinces with Bird Conservation Regions (BCRs, indexed here by their numbers). BCR names are: BCR 12, Boreal Hardwood Transition; BCR 13, Lower Great Lakes / St. Lawrence Plain; and BCR 6, Boreal Taiga Plains.

Mentions: As expected, trajectories from the trend models used by the USGS and CWS were more linear (i.e., showed fewer cycles and fluctuations) than trajectories generated by the spatial CAR model. In some strata and for some species (e.g., Olive-sided Flycatcher and Tree Swallow), there were only minor differences between the two models, particularly when there were many routes and years with observations in a given stratum (Fig 1A and 1B). By contrast for some strata and species, annual indices from the trend model were smoothed toward the estimated long-term trend in the population, and did not show the cycles or changes that were evident in the estimates from the spatial CAR model (Fig 1C and 1D).


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)

Comparison of Annual Indices of Abundance from the BBS Generated by the Annual Index Model (Spatial CAR) and by the Trend Model Currently Used by Environment Canada’s Canadian Wildlife Service (CWS Trend).Examples include plots for Olive-sided Flycatcher in Ontario/Bird Conservation Region (BCR)12 (A), Tree Swallow in Ontario/BCR 13 (B), Olive-sided Flycatcher in Quebec/BCR 12 (C), and Tree Swallow in Alberta/BCR 6 (D). Species and regions represent examples where the two models give very similar estimates (e.g. A and B), or very different estimates (e.g., C and D). Region names relate to analytical strata, which are defined by the intersections of Canadian provinces with Bird Conservation Regions (BCRs, indexed here by their numbers). BCR names are: BCR 12, Boreal Hardwood Transition; BCR 13, Lower Great Lakes / St. Lawrence Plain; and BCR 6, Boreal Taiga Plains.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130768.g001: Comparison of Annual Indices of Abundance from the BBS Generated by the Annual Index Model (Spatial CAR) and by the Trend Model Currently Used by Environment Canada’s Canadian Wildlife Service (CWS Trend).Examples include plots for Olive-sided Flycatcher in Ontario/Bird Conservation Region (BCR)12 (A), Tree Swallow in Ontario/BCR 13 (B), Olive-sided Flycatcher in Quebec/BCR 12 (C), and Tree Swallow in Alberta/BCR 6 (D). Species and regions represent examples where the two models give very similar estimates (e.g. A and B), or very different estimates (e.g., C and D). Region names relate to analytical strata, which are defined by the intersections of Canadian provinces with Bird Conservation Regions (BCRs, indexed here by their numbers). BCR names are: BCR 12, Boreal Hardwood Transition; BCR 13, Lower Great Lakes / St. Lawrence Plain; and BCR 6, Boreal Taiga Plains.
Mentions: As expected, trajectories from the trend models used by the USGS and CWS were more linear (i.e., showed fewer cycles and fluctuations) than trajectories generated by the spatial CAR model. In some strata and for some species (e.g., Olive-sided Flycatcher and Tree Swallow), there were only minor differences between the two models, particularly when there were many routes and years with observations in a given stratum (Fig 1A and 1B). By contrast for some strata and species, annual indices from the trend model were smoothed toward the estimated long-term trend in the population, and did not show the cycles or changes that were evident in the estimates from the spatial CAR model (Fig 1C and 1D).

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