24 



KEY TO LOONS 



1 Bill length 45-58 mm; wing length <316 mm (260-315); tarsus length 

 65-79 mm. 2 



T Bill 70-98 mm; wing >319 mm (320-395); tarsus usually >79 mm (73-97). 3 



2 Bill stiletto-shaped, tip of culmen curved decidedly downward (Plate 

 2-3). In spring or summer, throat black with green or purple irides- 

 cence; back black, each side of upper mantle with column of rectangular 

 white spots. In fall or winter, throat white; back blackish brown, 

 sometimes a few scapular feathers with each having a pair of dull 

 whitish spots. ARCTIC LOON 



2' Bill slender, appearing upturned due to (1) abrupt upward angulation 

 of lower edge, and (2) a straight (perhaps slightly downcurved) or 

 upward curved culmen especially along posterior two-thirds (Plate 2-2). 

 In spring or summer, throat red; back blackish-brown, feathers at 

 shoulder each with a pair of small gray spots at the tip. In fall or 

 winter, throat white; back blackish-brown, but each feather has a 

 pair of white spots at the tip. RED-THROATED LOON 



3 Culmen dark along entire (or almost entire) length; bill stiletto- 

 shaped, culmen curved downward (Plate 1-1); central portion of ventral 

 surface of outer 7 primaries light tan, bordered on either side with 

 dark tan; viewed from the front, cross section of bill anterior to 

 nostrils is rounded. COMMON LOON 



3' Culmen paler, horn color at tip and darkening toward base; culmen 

 often straight, distal one-third of lower mandible with abrupt 

 upward angle giving bill an upturned appearance (Plate 1-2); central 

 portion of outer primaries on ventral surface creamy, bordered on 

 either side by creamy to pale tan; viewed from the front, cross 

 section of bill anterior to nostrils often flat-sided. 



YELLOW-BILLED LOON 



