A species of bird had an original range covering the entire eastern half of the United States from ...

Among many observations that can be made, the researchers will have to look at the ability of eastern and western birds to recognize one another, court and mate. If mating does occur, they will have to observe whether or not any eggs are laid in the nest and whether any offspring hatch. They will have to discover whether the east-west matings produce more or less offspring than east-east and west-west matings. Finally, if offspring are produced and can in turn produce a second generation of hybrids, the researchers may conclude that these birds still function as a single species. If there are no viable hybrids or if the matings are blocked at an earlier stage, they may conclude that speciation has indeed taken place.

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