Species lines blur between two sparrows in New England's tidal marshes
Among birds, the line between species is often blurry. Some closely related species interbreed where their ranges overlap, producing hybrid offspring that can even backcross with either parent species, until a whole population of mixed-species birds forms in the area and creates what's known as a 'hybrid zone.' In the coastal marshes of New England, this has been happening between two sparrows—Saltmarsh Sparrow and Nelson's Sparrow. A new study published this week in The Auk: Ornithological Advances shows that appearance alone is not enough to identify these hybrid zone birds: there is no single, intermediate 'phenotype' or physical appearance common to all of the first-generation hybrids found, and birds from further backcrossed generations were often indistinguishable from the parent species. Fifty percent of birds identified as 'pure' Nelson's or Saltmarsh Sparrows in the field turned out be the descendants of hybrids when their DNA was analyzed.