A conceptual scheme of the model's main processes.

<p><i>Home-range</i> (left): A bird is introduced to a random forest cell (black spot) and occupies it as its “home-base” (dark blue); it moves randomly to any direction and occupies neighbouring cells (always returning to its home-base once occupying a new cell); in the expansion process it may occupy matrix cells (edge-penetration, left), thereby reaching other patches ( = connectivity) but with the cost of increasing the home-range size, or it may perform gap-crossing (right) and occupy cells in other patches without utilising matrix cells, (in which case the total number of cells until establishment may be smaller). Random-walk penetration into the matrix and gap-crossing are not mutually exclusive. <i>Dispersal</i> (righ): birds are introduced randomly into patches (not necessarily at the location where home-base are located), and move one step at a time – none of the cells is occupied. When reaching edges, birds may continue through the matrix (left path) or move between patches by means of gap-crossing. Simulation halts when arriving at a suitable patch (see text), or individuals may continue depending on a predetermined number of steps (dashed arrow).</p>