Recently, ENETWILD released a practical guidance to estimate wild boar population, relative abundance and density. The guidance is based on literature review as well as previous experiences from ENETWILD partners and external experts.
The general aim of this guidance was to review the accuracy and comparability of methods to estimate relative abundance and density of wild boar populations. For this purpose we reviewed and evaluated eighteen methods, the most suitable ones to estimate wild boar density on a local scale were recommended. Counting wild boar on a regional scale is unfeasible; therefore density estimations are reliable only at local scales in specific habitats. The available methods for wild boar population estimation (either direct or indirect methods depending on whether they are based on direct observation of animals or not) were classified according to desirable characteristics like practicability, applicability and accuracy.
Classification of available methods for estimating of wild boar density and relative abundance. The methods that are presented in the guidance are highlighted in bold.
On a local scale (e. g. in wild boar management units) and in specific habitats, density and relative abundance can be estimated. Methods traditionally used with other wildlife (mainly direct methods) are neither precise nor accurate enough to be considered as a gold standard. In the case of methods based on direct observation, the main limitation is related to the nocturnal habits of the wild boar species. The indirect methods, like count of faecal pellets, are too costly to produce accurate estimations of population density as they often require additional resources to calculate parameters that can only be used locally, such as defecation rates. We came to the conclusion that every method on estimating wild boar population has some advantages and disadvantages depending on the habitat, the weather conditions and the benefit.
Classification of different methods to estimate density and /or relative abundance based on desirable characteristics for monitoring populations (A=relative abundance, D=density) in local management units, practicability, and applicability in epidemiological aspects.
y=yes; ~=restricted; n=no; L=Low, H=High, M=Moderate, A=accuracy, P=precision; 1= (possible, but not usual); 2=yes with restrictions, 3= Maybe valid for monitoring and used as relative abundance for a given population, 4= Valid for monitoring along time and space as relative abundance when precision or accuracy is low; ; 5=possible, but…;
camera trapping (CT)
distance sampling with thermography
are especially recommendable to estimate wild boar density on a local scale and guidance for their implementation was provided.
Camera trapping, particularly, can be conducted everywhere, irrespective of the habitat specificities, and at any time producing comparable data.
While direct counting wild boar on a regional (large) scale is unfeasible to provide indications on long-term population trends, standardized hunting data (collected or sampled) at the lowest possible spatial resolution, e.g. at hunting ground level, have the highest availability and comparability potential across Europe to be used for predictive spatial modelling of wild boar relative abundance and even density.
Nevertheless, for wild boar management, hunting bag statistics will not be sufficient on their own. They do not show real population densities, they are influenced by several factors like weather conditions, nutrition, hunter’s behaviour, changes in hunting licensing, population densities and visibility: hunting bags may no be always related with the real trend of the population, but they reflect the hunting effort.
Nevertheless, depending on the needs, hunting bags may be sufficient e.g. for showing long-term trends and large-scale spatial epidemiology. Therefore, for spatial models at local scale and evaluation of management measures against disease spread, more precise information on population size (population size, densities, relative abundances) is needed.
General recommendations for practical implementation of methods to estimate wild boar relative abundance and density
- The sampling strategy should optimize accuracy while avoiding the bias of density estimations. The design of the study (sampling strategy) should be representative. This is especially true for wild boar that has an aggregated pattern of spatial distribution and marked habitat selection.
- Produce a method that provides density estimate rather than relative abundance should be used to camparable data, if and where possible.
- The estimation of abundance at local scale using direct counts might be the best solution for ASF management. In ASF affected areas, methods with little disturbance impact should be used, such as CT, which would be an independent, less disturbing, and practicable method to collect robust data and for longer term ASF risk assessment and management.
- The methods should be used in a harmonized way: we provide detailed instructions for the design of most recommended methods, but specific protocols must be specifically adapted to local conditions.
Apart from the elaborated methods for estimating wild boar relative abundance and density, we face a far larger challenge. Vitally important to analysis of data is the quantity, quality, reliability and distribution of data. Not every country has the necessary funds to estimate wild boar density on a large scale. There is a need for compiling and validating wild boar relative abundance and density data at different spatial scales. Hunting bags alone are not sufficient because a calibration with more accurate density estimation methods is required at a local scale. Local density estimates are also required to validate predictions in large areas and have also the potential to enable the conversion of relative abundances into predicted densities by use of modelling. To be able to receive enough data, we request hunters and wildlife managers to use a method where density estimation is performed, which should be accompanied by the collection of detailed hunting statistics.
Summarizing the main challenges regarding the estimation of wild boar relative abundance and density:
To improve the reliability of local density estimations:
o Implement research studies using camera trapping
o Training of local teams
To improve the estimates of wild boar population at large scale:
o Hunting data collection frameworks should be standardized and harmonized to validate and make them comparable across Europe;
o Involving the national and regional hunting administrations in data collection and sharing, as well as the hunters associations;
o Collecting local hunting statistics based on comparable hunting modalities across Europe;
o Collecting hunting effort and efficiency in a set of representative wild boar populations;
o Evaluating the relationships between local densities and hunting statistics, how they vary across Europe, and the determinants.
To improve the modelling of wild boar distribution and abundance across Europe using reliable estimates of wild boar population at local and large scales:
o Improve the spatial modelling of wild boar distribution and abundance across Europe requires the use of reliable estimates of wild boar population at local and large scale for appropriate model input and validation.
o Data obtained by different methods cannot directly be combined by simple equations but complex spatial models are needed to determine abundance and/or predicted densities that are reliable at larger scales;
o Taking advantage of citizen science to feed models on distribution and abundance with data targeting gap areas.