Understanding how human activities drive biodiversity change at different spatial scales is a key question for conservation practitioners and decision-makers. While we have a good understanding of the primary causes of observed biodiversity declines – which include land-use change, climate change, pollution, and the over-exploitation of species – we still struggle to measure and detect biodiversity change in robust and meaningful ways.
This piece of research explores the question of measuring and detecting biodiversity change for European birds, which are well monitored in many European countries thanks to ongoing monitoring programmes. Using datasets on breeding bird assemblages in the United Kingdom and the European Union, the authors examine changes in the total estimated number and biomass of birds over several decades. Through this approach they seek to tackle the questions of whether avian biodiversity, as measured by species abundance and biomass, has changed in these two bird assemblages and whether patterns of change differ at these two spatial scales.
The results of this study reveal significant changes in the bird assemblages of the UK and EU, with substantial reductions in overall bird abundance. The authors estimate that the total number of native breeding birds in the UK declined by 38 million individuals (19%) between 1966 and 2018. The figure for the EU is a decline of 550 million individuals (17%) between 1980 and 2017. Over the same period, the study shows overall avian biomass to have increased very slightly in the UK and to be stable in the EU, indicating a change in community structure.
The losses are concentrated in a relatively small number of abundant and smaller sized species, including House Sparrow, Starling, Willow Warbler and Wren. In contrast, rarer and larger birds had generally fared better. Abundance trends across species were positively correlated with species’ body mass and with trends in climate suitability. They were also found to have varied with species’ abundance, migration strategy, and niche associations linked to diet.
The work highlights how changes in biodiversity cannot be captured easily by a single number, identifying the need for care when measuring and interpreting biodiversity change, and consideration of the metrics used.
Detecting biodiversity change and identifying its causes is challenging because biodiversity is multifaceted and temporal data often contain bias. Here, we model temporal change in species' abundance and biomass by using extensive data describing the population sizes and trends of native breeding birds in the United Kingdom (UK) and the European Union (EU). In addition, we explore how species’ population trends vary with species' traits. We demonstrate significant change in the bird assemblages of the UK and EU, with substantial reductions in overall bird abundance and losses concentrated in a relatively small number of abundant and smaller sized species. By contrast, rarer and larger birds had generally fared better. Simultaneously, overall avian biomass had increased very slightly in the UK and was stable in the EU, indicating a change in community structure. Abundance trends across species were positively correlated with species’ body mass and with trends in climate suitability, and varied with species' abundance, migration strategy and niche associations linked to diet. Our work highlights how changes in biodiversity cannot be captured easily by a single number; care is required when measuring and interpreting biodiversity change given that different metrics can provide very different insights.
Notes
We thank the many volunteers who contributed to national bird surveys and the scheme coordinators (Hany Alonso, Marc Anton, Ainars Aunin¸š, Zoltán Benkő, Mattia Brambilla, Malte Busch, Gianpiero Calvi, Tomasz Chodkiewicz, Przemyslav Chylarecki, Jordi Dalmau, Elisabetta de Carli, Juan Carlos del Moral, Antoine Derouaux, Jaanus Elts, Virginia Escandell, Daniel Palm Eskildsen, Lorenzo Fornasari, Benoît Fontaine, Ruud P.B. Foppen, Bettina Gerlach, Sarah Harris, Henning Heldbjerg, Sergi Herrando, Iordan Hristov, Magne Husby, Christina Ieronymidou, Frédéric Jiguet, John Atle Kålås, Johannes Kamp, Primož Kmecl, Friederike Kunz, Petras Kurlavicius, Aleksi Lehikoinen, Domingos Leitão, Meelis Leivits, Lesley Lewis, Åke Lindström, Dario Massimino, Renno Nellis, Daniel Palm Eskildsen, Alain Paquet, Jean-Yves Paquet, Clara Pladevall, Danae Portolou, Ingar Jostein Øien, Cindy Redel, Jiří Reif, Jozef Ridzoň, Hans Schmid, Laura Silva, Nicolas Strebel, Zoltán D. Szabó, Tibor Szép, Guido Tellini Florenzano, Joaquim Teodósio, Norbert Teufelbauer, Sven Trautmann, Tom van der Meij, Chris van Turnhout, Glenn Vermeersch, Zdeněk Vermouzek, Thomas Vikstrøm, Anne Weiserbs) and those who submitted data across the EU. We thank Andy Gonzalez, Mary O'Connor, Edward Tekwa, Tim Blackburn and two referees for valuable discussions and comments on the manuscript.
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