147 



CASPIAN TERN (sterna aaspia; choices 9 and 9', pg. 63). Like the 

 latter two, this species is quite distinctive from other terns, 

 particularly oecause of its size. If one picked up a Red-billed Tropicbird, 

 until a closer look was made, the Caspian Tern would probably be the first 

 name to come to mind. They both are very light in coloration, are of 

 similar size, and have large heavily proportioned red bills; compare 

 Plates 4 and 29. It is, of course, far more likely to find a Caspian Tern 

 in North American coastal waters than it is a tropicbird. 



This species can be found year round in coastal waters from southern 

 California southward, but more so during fall and winter. It occurs 

 rather rarely along the Pacific coasts of Oregon and Washington during 

 spring and fall migrations. 



BLACK TERN (Chlidonias nigra; choices 3 and 3', pg. 62). An adult of 

 this species is superficially similar to a juvenile Sooty Tern, but the 

 larger size and buffy feather margins of the latter would readily 

 separate the two species. 



Black Terns wander a good deal and thus one might conceivably 

 encounter one in coastal waters as far north as Washington. Finding one 

 is much more likely from California southward. The species breeds inland 

 and winters from Panama southward. Thus it would occur off here mainly 

 during migration, and especially the fall. 



SKIMMERS (RYNCHOPIDAE) 



BLACK SKIMMER (Rynchops niger; choices 6 and 6', pg. 62). Except for 

 its very distinctive bill (Plate 29), this bird is similar in morphology 

 to terns. There should be no problem in distinguishing a specimen of 

 this species. 



Black Skimmers breed coastal ly in southern California on San Dieqo Bay 

 In the region covered by this manual, one is most likely to find them from 

 southern California southward and very rarely as far north as central 

 California. Any specimen found should be saved for verification. 



ALCIDS or AUKS (ALCIDAE) 



Auks are compact and, compared to their wing size, rather heavy-bodied 

 birds. Their wings are surprisingly narrow, as in a petrel, but are 

 rounded rather than pointed. Many auk species have a brightly colored 

 bill, mouth lining and feet (colors include yellow, orange, bright red 

 and blue). They can offer some of the most difficult problems in identi- 

 fication for two reasons. First, the young of larger species are super- 

 ficially similar in size and shape to adults of smaller species. The 

 young of most seabirds leave the nest or nesting island when "adult-sized" 

 but the young of some alcids leave nesting islands when very small and in 

 some cases when just a few days old. Many times young murres have been 

 identified as murrelets. Second, most morphological variation among auks 

 is confined to differences in size and in head characteristics. Thus in 

 a headless specimen only size and some subtle color differences can offer 

 clues to identification. 



