What is the distribution map colour key?

Yellow is used to indicate zones habitually occupied for breeding, but where the species is not normally present outside the breeding season.

Blue indicates zones occupied by the species, where it does not normally breed, or where breeding is suspected by has not definitely been recorded; thus, these colours should not be interpreted exclusively as summer and winter distributions, a regular practice in many bird guides, especially in temperate zones.
On the maps of a few species, the only area shaded is blue; this means that in these species, usually seabirds, the general zone occupied is known, but the breeding grounds have not yet been located.

Green is used to indicate areas where the species tend to be present all year round, although this does not preclude the possibility of erratic or dispersive movements, or even partial migration.