Snow Geese © Rinusbaak/Dreamstime.com

Action is urgently needed to halt human-induced extinction of species and stem the loss of natural habitats. The world’s governments have made commitments through the Convention on Biological Diversity (CBD) to tackle this issue, and the CBD has proposed 20 targets for 2020 in order to focus action. It is vital, therefore, that simple and effective indicators are developed to track progress towards achieving these targets.

Making sense of indicators Biodiversity indicators are easier to understand, communicate and act upon when linked together in a set that connects policies to outcomes. Four kinds of indicators are needed to make a joined-up set - response indicators, which gauge the impact of policy actions: pressure indicators, which evaluate the threats facing biodiversity; state indicators, which reveal the current status of biodiversity and benefit indicators, which measure how nature contributes to human wellbeing.

To coincide with the tenth Conference of the Parties to the CBD, held in Nagoya, Japan, BirdLife published a booklet entitled Meeting the 2020 biodiversity targets: action and monitoring based on birds. It outlined how the wealth of data available for birds could be used to help set priorities for action and to track the success or failure of society’s response to the unfolding biodiversity crisis. This was updated in Developing and implementing National Biodiversity Strategies and Action Plans, which showed how imformation from birds can be used to set, meet and track 18 of the 20 Aichi Biodiversity Targets. Birds are an ideal indicator group: they are widespread, comparatively well studied, and highly responsive to environmental change (, ).

Birds can provide data for practical, quantitative assessment of our success or failure in preventing extinctions and improving the status of species. The IUCN Red List Index (RLI)—based on data on the movement of species through categories of extinction risk—shows that the status of bird species globally has declined steadily over the last two decades (). The RLI can also quantify the net impact of different threats to biodiversity. For example, the impact of overfishing and destructive fishing practices is illustrated by the RLI for seabirds which shows that marine species are more threatened and have declined faster than any other avian group (, ). Other RLIs show the impact of invasive alien species, pollution and other drivers, or trends in sets of species important for delivering particular ecosystem services, such as pollination. National RLIs based on assessment of extinction risk at a national scale are becoming increasingly available.

Important Bird Areas (IBAs) represent a core set of the most important sites for biodiversity conservation across the globe. The IBA Protection Index measures the degree to which these priority sites are covered by protected areas and provides a useful metric to judge progress in reducing biodiversity loss (). Currently, only 39% of the area of each IBA is protected on average, and only 26% of sites are completely protected. IBAs across the world are being monitored using BirdLife’s systematic IBA monitoring protocol for tracking trends in the condition of these sites, the pressures upon them and conservation responses in place. IBA indices based on these data indices show that sites with formal protection are in better and more stable condition than those without (). Targeting future expansion of protected area networks at IBAs will help countries achieve their commitments under Aichi Target 11, given this calls for protected areas to cover “especially areas of particular importance for biodiversity”.

Birds are useful indicators of the rate of loss and degradation of different habitats. Wild Bird Indices illustrate trends in the average population abundance of sets of species characteristic of different habitats. These show that woodland bird populations in Europe have undergone a shallow decline since 1980, whilst farmland birds have declined much more steeply (). In North America, grassland bird populations have declined by over a quarter in the last four decades (). The systematic bird population monitoring schemes that provide the data underpinning Wild Bird Indices are now being established outside Europe and North America, particularly in Africa.

These data can also be used to monitor trends in the impact that climate change is having on biodiversity. The Climatic Impact Index for European birds is produced by using projections from climate envelope models to identify which species are likely to benefit or suffer under climate change, and then using bird population monitoring data to calculate average trends in the population abundance of these two groups. This shows a strong signal of the impact of climate change on European bird populations since about 1990, and that, over the last two decades, three times as many species have been negatively impacted by climate change than positively affected ().

Biodiversity concerns need to be incorporated into national planning across all sectors of government. Data from birds can be used to ensure this is done effectively, and to monitor the degree to which development is sustainable. For instance, the UK government has adopted an index based on wild bird populations as one of its 15 headline Quality of Life indicators (). Effectively tackling the biodiversity crisis will also rely on building awareness and engendering public support. Birds are spectacularly popular and provide an excellent measure of public engagement with biodiversity. Monitoring the number of people participating in bird-related activities can provide a simple measure of progress in raising environmental awareness ().

CBD Parties are required to prepare National Reports on the status of implementation of the Convention. As conservation priorities for birds are better known than for other species groups, data on birds can help to target national activities on the most urgent issues, species and places. Since the first National Reports were produced in 1998, the emphasis placed on threatened bird species and IBA conservation has increased considerably ().

Given the strength of birds as indicators, it is unsurprising that BirdLife’s indicators have also achieved wide policy uptake, for example by the United Nations as indicators for the Millennium Development Goals, the Ramsar Convention on Wetlands, the Convention on Migratory Species and its daughter Agreements, the European Union, and by many national governments. They have also featured prominently in global reports on the state of the planet, such as the Global Biodiversity Outlook, Global Environmental Outlook, and Protected Planet Report.