Species pairTwo very closely related and very similar species, for example the Crossbill Loxia curvirostra and the Scottish Crossbill L. scotica. In such cases there is often some doubt over the justification for regarding the two as separate species, and the Scottish Crossbill might be considered by some ornithologists to be simply a subspecies of the Crossbill. A group of very closely related species may be called a superspecies.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver