State of nature 2023 terrestrial and freshwater animal dataset for the United Kingdom and its constituent countries

This article describes the terrestrial and freshwater animal trend data used in creating the 2023 State of Nature reports for the UK and its constituent countries. Trend data for long- (1970–2020/21) and short-term (2010–2020) periods have been calculated by fitting statistical models to measures of abundance (753 species) or occupancy (4979 species) across the UK. Trend data was also calculated for each constituent country: England, Northern Ireland, Scotland and Wales for reduced sets of species.
Trends in abundance data were generally created from the analysis of repeat counts at specific sites. Trends in occupancy were created by analysing ad hoc species records of invertebrates provided by volunteers. Statistical methods partially controlled for the risk of bias and the noisy nature of such occupancy data. Trends were only calculated where the number of species records justified the creation of trend statistics.
Species that make up three key groups of insects are identified in additional columns in the dataset, those responsible for key ecosystem functions: species providing freshwater nutrient cycling, pollinating insects and predators of crop pests.
The data has one clear limitation in that it is only a partial representation of the fauna of the UK. Many cryptic, nocturnal or soil dwelling species are poorly recorded and even some easy to identify species such as amphibians and reptiles do not have a suitable recording scheme that captures abundance.