Specimens of the same species must remain in contact with each other to ensure survival and development of the whole species. Splitting larger populations in smaller, separately living groups decreases their chances of survival in a changing environment. Lack of the possibility to exchange genes during reproduction leads to dying out of populations and whole species.

Some species, especially larger predators need large hunting grounds to live on. This area must be even larger if the amount of prey that is possible to catch is small. That is why there is as little as 200 specimens of lynx living in Poland. Large areas of forest are very scarce in our country and it cannot support larger populations of lynx. One male lynx needs an area of 350 sq kilometres of forest to live on and females need 150 sq km of forest for their hunting ground.

Moreover, each pair of breeding birds requires a designated fragment of forest. An isolated part of forest with the area smaller than required by a certain species will not be "colonized" because it will not provide enough food and shelter. The same applies to different species of bats inhabiting forests.

Over 6000 forest groups in Poland occupy an area of 5 ha or smaller. These areas are too small for most forest animals and remain unoccupied. Only species that are not very demanding in terms of space or those which can combine couple of neighbouring small forests as their living ground inhabit those areas.

To improve the living conditions for species cut off from the rest of the world in their small enclaves, such "islands" of precious habitats should be connected by ecological corridors. Ecological corridor is a line of habitats less changed by humans, which provide safe conditions for spreading of species inhabiting isolated ecosystems. Although there are "gaps" in the range of certain species, such corridors create an opportunity for some specimens to pass these "gaps".

This gives the possibility for different populations to have contact with each other. Animals can roam relatively safe and plants have the opportunity to spread pollen on neighbouring territory occupied by the same species. It is very important to ensure that ecological corridors give the animals an opportunity for safe migration. Numerous species of birds, fish, bats and some insects often migrate over great distances. Big mammals also roam in search of food and shelter – one of the most persistent migration species in this group is a common wolf.

Migration corridors of big mammals extend from east to west, mostly along rivers and river valleys. To use this routes animals must have the longest possible sections of forest with enough food supply along those migration corridors. These routes are often divided by barriers like roads and freeways which are impossible to cross for animals. Passages for animals should be build under or over the roads which divide animal migration routes.

To protect natural migration routes of birds we should preserve forests along the Baltic coast, forests, bushes and coastlines in the valleys of big rivers and all water basins – especially those with shallow and muddy shores.