Do we have to worry about each local decline of a species? For this may be compensated by increases elsewhere, resulting in a stable species trend.
Answer On principle, each decline is to be taken seriously if it is persistent. Normally, each area is saturated with the species that live there: it holds the number of individuals of each species that it can house (ecological term: carrying capacity). When in one region the carrying capacity for a species is lowered, for instance by agricultural intensification or forest logging, there is no way for individuals to take refuge to other suitable areas, as these will be saturated already. So, no compensation will occur and each local decline has its repercussion on national and supra-national population numbers.