Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Mercer, D.M., S.M. Haig, and D.D. Roby. 2013. Phylogeography and population genetic structure of double-crested cormorants (Phalacrocorax auritus). Conservation Genetics 14:823-836. doi: 10.1007/s10592-013-0477-8.


Increases in double-crested cormorant populations since the mid-1970s, especially in central and eastern North America, have raised concerns about effects on fishing resources. Management of different populations of these seabirds have not accounted for genetic differences, which could have implications for scarce subspecies. Four subspecies have previously been described, but detailed genetic analyses have not confirmed this. Oregon State University graduate student Dacey Mercer, along with USGS advisors Susan Haig and Daniel Roby, examined the genetic structure of double-crested cormorants by analyzing DNA in birds’ blood or tissue collected across North America. Analyses confirmed the presence of two subspecies, one from Alaska and one associated with the southwestern portion of the species' range. Small genetic differences found among birds from other regions were related to gradual isolation by distance. Documented declines in Alaskan double-crested cormorants could warrant conservation of this unique subspecies.