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Wild mammals are making a comeback in Europe thanks to conservation efforts

Long-term monitoring of wildlife populations is difficult. The methods used and the quality of estimates can change and improve over time. In this ass

Long-term monitoring of wildlife populations is difficult. The methods used and the quality of estimates can change and improve over time.

In this assessment, for each mammal, researchers drew on published studies that assessed the most recent population estimates, and the change over time. These are population estimates that are included in the Living Planet Index. To address the limitations of changes in data collection, the authors only include analyses where the same methods are applied over the same time series, and the data is transparent and traceable.

This means that the data coverage may vary from species-to-species. For some species we have good estimates for all countries in Europe where it is present. For other species,it may only be a subset of countries where it can be found. One example here is the Eurasian beaver: the study did not include consistent data for beaver populations across some parts of Russia and it populations outside of Europe, in Asia. That means the total figure for Eurasian beavers does not reflect the complete total. However, the change over time is reflective of the true change across the countries and regions include i.e. the geographical scope of the estimates in the start and end year are the same.

The authors do not include the starting (e.g. 1960) population levels for each mammal species in absolute terms in the report. Instead, they report the latest estimate (e.g. for 2011) for each species; and the estimated level of increase since the baseline year 1960.

I have combined both of these numbers to estimate the population levels in the baseline year. For example, they estimate that there were 2759 European bison in the latest estimate, and that populations have increased by 3000% since 1960. I calculate that this would mean there were around 89 European bisons in 1960. We get this as: [ 2759 / (3000% + 100%) ] = 89.

These are estimates and come with some uncertainty. To not overstate the level of precision, I have rounded the figures for the start year to the nearest ten, hundred or thousand depending on the population size for each species.