COS 84-5
Are they really declining? The effect of inconsistent definitions on bird trends
We live in an age of pressing ecological problems associated with habitat destruction, introduced species and climate change. Investigating these problems increases our ability to deal with them, but only if each study builds on those before it. Consistent definitions, measures and methods make studies comparable and ensure that they add to accumulated knowledge.
One pressing ecological problem is the decline in woodland and farmland birds across Europe and Australia. A plethora of studies investigate the reasons for this decline. However, if the bird groups aren’t defined consistently, the perceived trends over time will differ. Using a systematic review and data on the prevalence of Australian and European birds over 17 years, we answer the questions: Are different researchers classifying woodland and farmland birds differently? and How does this affect the perceived trends in their prevalence?
Results/Conclusions
We found substantial inconsistencies in how authors define woodland and farmland birds in both Europe and Australia. These inconsistencies correspond to significantly different conclusions about their prevalence.
The prevalence of Australian woodland birds is believed to be dangerously low. However, our results suggest that, depending on how they are defined, woodland bird prevalence may vary by up to 230%, drawing this belief into question. In Europe, farmland birds are believed to be declining but our results show that, depending on how they are defined, their prevalence may be decreasing or increasing.
There is no official definition of woodland or farmland birds and it is left to authors’ discretion to operationalise these terms. As a result, researchers define these groups differently and reach different conclusions. Given the lack of officially defined terms in ecology more broadly, we expect this problem to be widespread, slowing progress towards understanding and solving pressing ecological problems.