172 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 150 



They are active when feeding, particularly when caring for young, 

 but at other times may remain quietly on some perch for long pe- 

 riods and so escape attention. Only part of the tropical species appear 

 to soar with any regularity in the open air above the forest. 



In addition to the resident kinds a few others come during the 

 northern winter. Among these the migrant flocks that pass over the 

 isthmus twice each year, en route to and from winter homes in 

 South America, form one of the spectacular sights of the bird world. 



KEY TO SPECIES OF ACCIPITRIDAE 



1. Tail long and deeply forked. .Swallow-tailed kite, Elanoides forficaius, p. 175 

 Tail not deeply forked 2 



2. Side of maxilla with two deep notches on margin separating two distinct 



toothlike projections. 



Double-toothed kite, Harpagiis bidentafus jasciatus, p. 184 

 Side of maxilla not double-toothed on margin 3 



3. Tarsus short and heavy ; length less, or only slightly more, than middle toe 



with claw 4 



Tarsus proportionately longer; length decidedly more than middle toe with 

 claw 8 



4. Maxilla narrow, in proportion to its width at base, the tip produced in a 



slender, elongated hook 5 



Maxilla not excessively slender or elongated in proportion to its width at 

 base 6 



5. Tail long, more than 150 mm. ; wing more pointed, distance between tips of 



longest primaries and longest secondaries more than 80 mm. 



Everglade kite, Rostrhamus sociabilis sociabilis, p. 180 

 Tail short, less than 140 mm. ; wing rounded, distance between tip of longest 

 primaries and longest secondaries 50 mm. or less. 



Slender-billed kite, Helicolestes tiamatus, p. 182 



6. Inner webs of outer primaries chestnut. 



Plumbeous kite, Ictinia plumbea, p. 177 

 Inner webs of outer primaries without chestnut 7 



7. Tarsus less than 40 mm. ; bill strongly compressed, with narrow, elongated 



tip Hook-billed kite, Chondrohierax uncinatus uncinatus, p. 188 



Tarsus 42 to 51 mm.; maxilla swollen laterally, with tip broader and less 

 elongated Cayenne kite, Leptodon cayanensis cayanensis, p. 186 



8. Head conspicuously crested 9 



Head not conspicuously crested 13 



9. Size very large, wing more than 500 mm.; feet unusually strong and 



powerful Harpy eagle, Harpia harpy ja, p. 249 



Size smaller, feet normal in size 10 



10. Tarsus feathered to the toes 11 



Tarsus bare except at upper end. 



Crested eagle, Morphnus guianensis, p. 246 



11. Under surface white, without dark markings. 



Black-and-white hawk-eagle, Spisastur melanoleucus, p. 244 

 Under surface mainly black, or white barred with black 12 



