Network Ecological Monitoring (NEM)
Many of the mammal species are not monitored, because this is not (yet) possible. For example, bats and martens are active at night or inhabit inaccessible places, so systematic counts cannot be made, or the cost is too high. Another reason for the absence of a species in the trend indicator of mammals is that species that reproduce continuously in the Netherlands for less than 10 years do not have to be reported to the European Union. As a result, wolves and wildcats, for example, are not yet covered by the NEM.