Global abundance estimates for 9,700 bird species

Abstract

Quantifying the abundance of species is essential to ecology, evolution, and conservation. The distribution of species abundances is fundamental to numerous longstanding questions in ecology, yet the empirical pattern at the global scale remains unresolved, with a few species’ abundance well known but most poorly characterized. In large part because of heterogeneous data, few methods exist that can scale up to all species across the globe. Here, we integrate data from a suite of well-studied species with a global dataset of bird occurrences throughout the world—for 9,700 species (∼92% of all extant species)—and use missing data theory to estimate species-specific abundances with associated uncertainty. We find strong evidence that the distribution of species abundances is log left skewed: there are many rare species and comparatively few common species. By aggregating the species-level estimates, we find that there are ∼50 billion individual birds in the world at present. The global-scale abundance estimates that we provide will allow for a line of inquiry into the structure of abundance across biogeographic realms and feeding guilds as well as the consequences of life history (e.g., body size, range size) on population dynamics. Importantly, our method is repeatable and scalable: as data quantity and quality increase, our accuracy in tracking temporal changes in global biodiversity will increase. Moreover, we provide the methodological blueprint for quantifying species-specific abundance, along with uncertainty, for any organism in the world.

Species Traits Drive Long-Term Population Trends of Common Breeding Birds in Northern Italy

“…Population trends represent one of the most informative proxy of the status of populations’ health, from local to continental spatial scales. One of the most monitored taxa worldwide are birds [ 4 , 5 ], an animal group of large conservation interest, target of several conservation policies in different countries, as well as at a continental scale (e.g., Birds Directive 2009/147/EC in European Union). From the past century, many bird monitoring programs have been started in many countries worldwide, both at a continental scale (e.g., the Pan-European Common Bird Monitoring Scheme—PECBMS—in Europe [ 6 ], the North American Breeding Bird Survey—BBS—[ 7 ]) and at a national scale (e.g., in Finland [ 8 , 9 ], the Breeding Bird Survey—BBS—in UK [ 10 ]).…”

Power laws govern the abundance distribution of birds by rank

“…Therefore, the impact of the big four's extinction dramatically increases the overall uncertainty for the other species. Callaghan et al (2021) correctly observe that many species in their data have minimal population estimates, and relatively few species are very abundant. There are about 200 more species than expected if bird species abundance followed a truly log-normal distribution.…”

“…There are about 200 more species than expected if bird species abundance followed a truly log-normal distribution. Nevertheless, they settle for a log left-skewed distribution (Callaghan et al 2021) rather than the power-law distribution we consider here. The flexibility of the log left-skewed distribution accommodates the data well, but the Pareto seems more compelling for our piecewise approach.…”

“…The species abundance distribution is one of the few universal patterns in ecology (Morlon et al 2009). A new study found that bird species with fewer individuals are abundant, but large species are rare (Callaghan et al 2021). The researchers considered the recent influx of citizen science data to make the number of individuals (abundance) estimates for 9,700 species, about 92 percent of all birds.…”

Field studies need to report essential information on social organisation – independent of the study focus

“…Many researchers focused on getting a large, instead of an accurate, database, for example by using phylogenetic inferences to add species that had not been studied (birds: Cockburn, 2006; used also by Gonzalez et al, 2013;Jetz & Rubenstein, 2011;mammals: Lukas & Clutton-Brock, 2013). There are now statistically sound methods to infer missing phylogenetic data points (for example see Callaghan et al (2021)). This can be important to include species into the database for which information on the social system is missing, but for which important life-history and ecological data are available.…”