Collared Dove

It combined several advantages at the right moment. It feeds mainly on grain and lives alongside people, so the spread of farming, grain storage, stables, and garden bird feeding across the twentieth century created a continuous ribbon of food and nest sites for it to follow. It breeds prolifically, with several broods a year, and young birds disperse strongly in one direction, so a population builds and pushes outward year after year. From its older range around the Middle East and northern India it moved north-west across Europe from the 1900s, and a separate introduction to the Bahamas in the 1970s launched an equally rapid takeover of North America. The expansion is one of the best-documented natural range shifts of any animal.

Size and colour, mostly. The collared dove is smaller and slimmer, about 32 cm, a uniform pale sandy grey-buff with a thin black half-collar on the hindneck and dark wingtips, and it has a long tail with white outer corners seen from below. The wood pigeon is much bigger and bulkier, about 41 cm, blue-grey with a pinkish breast, bold white patches on the sides of the neck, and a broad white bar across each wing in flight. Their calls differ too, the collared dove giving a flat three-note coo and the wood pigeon a fuller five-note phrase. The collared dove also often gives a harsh, nasal call as it lands.

It depends on the region, and in most places the honest answer is that it arrived recently under its own power or with a small human push. In Britain and northern Europe it is a natural colonist that was absent until the mid-twentieth century and is now common. In North America it descends from birds that escaped in the Bahamas in the 1970s and is therefore an introduced species, though it spread across the continent on its own. Only in parts of southern Asia and the Middle East is it a long-standing native. Because it has caused little obvious harm, it is not usually treated as an invasive pest even where it is non-native.

Research so far has found little evidence that the collared dove displaces or reduces native birds where it has spread. It occupies a niche, feeding on grain in and around human settlement, that was not fully used by other species, and it does not appear to compete strongly with native doves such as the mourning dove in North America or to spread disease at a damaging level, although it can carry the parasite that causes trichomonosis. Its arrival is more a case of an empty seat being filled than of a resident being pushed out, which is part of why it is watched with interest rather than alarm.