Impact of climate change on bird populations

Assessment versions

Published (reviewed and quality assured)

• No published assessments

Rationale

Justification for indicator selection

MAIN ADVANTAGES OF THE INDICATOR

Although the indicator provides a simple visual depiction of the impacts of climatic change on bird populations through time, the underlying modelling of bird trends and climatic envelopes for species are complex (although fully documented in a peer-reviewed paper). Climatic warming has led to a small number of bird species increasing in number in Europe, but a much larger number declining in number, so overall climatic change poses a threat to biodiversity, but individual species might still benefit from a warming environment.

Scientific references

• No rationale references available

Indicator definition

The Climatic Impact Indicator (CII) measures the divergence between the population trends of bird species projected to expand their range, and those predicted to shrink their range due to climatic change. The indicator is based on a combination of observed population trends monitored from 122 common bird species in 20 European countries over 26 years, and projected potential shrinkage, or expansion, of range size for each of these species at the end of this century (~2070-2099), derived from climatic envelope models. The ensemble in this case is the average climate envelope forecast based on six differing future scenarios.

Units

weighted index (relative values)

Policy context and targets

Context description

Climate change is having a detectable effect on bird populations at a European scale, including evidence of negative as well as positive effects on their populations.

The number of bird species observed to be negatively impacted by climatic change is three times larger than those observed to be positively affected by climate warming in this set of widespread European land birds.

The Climatic Impact Indicator (CII), which illustrates the impact of climate change on bird populations, has increased strongly in the past twenty years, coinciding with a period of rapid climatic warming in Europe.

Potential links between changes in bird populations and ecosystem functioning and resilience are not well understood. It is suggested that increasing climatic effects might alter ecosystem functioning and resilience.

Relation of the indicator to focal area

Relation of this indicator to other indicators

Targets

No targets have been specified

Related policy documents

No related policy documents have been specified

Methodology

Methodology for indicator calculation

The CII is calculated in two steps. First, we divided the 122 bird species into those for which the ensemble climatic envelope model projection indicated an increase in potential geographical range (30 species) and those with projected decreases in geographical range (92 species).  For each of the two groups of species, we then calculated a multi-species population index from population indices for individual species, with the weight of the contribution of each species to the index being based on the modelled projected change in potential range extent. Extreme projections of range increase, or loss, for individual species thus have greater influence on the line. In simple terms, population trends of birds predicted to be strongly affected by climatic change in our models (either negatively or positively) strongly influence the direction of the lines shown in the sub-indicator figures.  For example, the Sardinian Warbler, Subalpine Warbler, Bee-eater and Cirl Bunting are increasing strongly and are projected to do so.  The snipe Meadow Pipit, Brambling and Willow Tit are declining strongly and are projected to do so.

In the second step, the CII itself is calculated in a given year as the ratio of the index for those species projected to increase in potential range (30 species) to the index of those species projected to decrease in geographical range (92 species).  The two lines have equal weighting in the indicator.

The CII shows conformity between observed population trends and projections of how each species' population should respond to climatic warmingThe CII increases when population trends go in the direction predicted by the modelsThe CII decreases when population trends go in the opposite direction predicted by the models.

In the analysis, we also looked at the influence of the habitat choice of the birds, their migratory behaviour and their body mass (as a proxy for life history characteristics) in predicting bird trends and in potentially influencing the CII.  Although population trends covary with these factors (e.g. farmland birds and long-distance migrants have declined strongly) these correlations do not confound the relationship between trends and the climate projections, nor do they confound the CII.
The methodology developed here is equally applicable to any other species group where equivalent information is available. For full methods and discussion, see Gregory et al. (2009) An indicator of the impact of climatic change on European bird populations (In press).

The indicator is based on the combination of two data sets:

1.  Population trend data on 122 common and widespread bird species for any part of the period 1980 - 2005 in 20 European countries (from the Pan-European Common Bird Monitoring Scheme: PECBMS). See Gregory et al. 2005, 2008
2. Climatic envelope model projections for each of the 122 species for the simulated future 2070-2099 showing an expanding potential geographical range or a decreasing potential geographical range. These are based on an ensemble forecast built on three General Circulation Models and two IPCC SRES emissions scenarios. See Gregory et al. In press, Huntley et al. 2007, 2008.

Methodology for gap filling

N/A

Methodology references

No methodology references available.

Data specifications

EEA data references

• No datasets have been specified here.

External data references

• Trends of common birds in Europe
• Ensemble forecast built on three General Circulation Models and two IPCC SRES emissions scenarios (dataset URL is not available)

Data sources in latest figures

Uncertainties

Methodology uncertainty

No uncertainty has been specified

Data sets uncertainty

No uncertainty has been specified

Rationale uncertainty

MAIN DISADVANTAGES OF THE INDICATOR

Although the indicator provides a simple visual depiction of the impacts of climatic change on bird populations through time, the underlying modelling of bird trends and climatic envelopes for species are complex (although fully documented in a peer-reviewed paper). Climatic warming has led to a small number of bird species increasing in number in Europe, but a much larger number declining in number, so overall climatic change poses a threat to biodiversity, but individual species might still benefit from a warming environment.

ANALYSIS OF OPTIONS

Climate change is having a detectable effect on biodiversity at a European scale, including evidence of negative as well as positive effects on their populations.

Work description

Resource needs

No resource needs have been specified

Status

Deadline