A lask a is th e cen tre o f a b u n d a n c e fo r N o rth A m erica's nestin g sw ans. T h e W histling Sw an Cygnus colum bianus columbianus nests on th e tu n d ra o f w estern an d n o rth e rn A lask a an d east to H u d so n B ay in C an a d a w ith th e g reate st den sity o c c u rrin g o n th e 26.000 sq. m iles (67,340 sq. km) o f th e Y ukon R iver D elta. T h e T ru m p e te r Sw an Cygnus Cygnus buccinator fo rm erly nested th ro u g h o u t a larg e p o rtio n o f w estern N o

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... A m eric a b u t is now confined to a few isolated locatio n s in o r n e a r th e R ocky M o u n tain s an d to p o rtio n s o f th e fo rested regions o f A lask a. T o d a y A la sk a hosts ab o u t th re e-fo u rth s o f th e nestin g p o p u la ­ tio n o f T ru m p e te r Sw ans an d p e rh ap s tw o-th ird s o f th e W histling Sw ans. T h ere a re ab o u t 22,000 sq. m iles (56,980 sq. km) o f T ru m p e te r h a b ita t in A la sk a a n d som e 72.000 sq. m iles (186,480 sq. km) o f W h istler h a b ita t. S tragglers from each species a re o ccasio n ally fo u n d w ithin th e ra n g e o f th e o th e r b u t essen tially th ey use w e ll-sep arated b re e d in g a re a s (F ig­ u re 1). D ow n th e years, n a tu ra lists h av e re ­ co rd ed o b serv atio n s o f sw ans in A la sk a b u t b e cau se o f th e larg e te rrito rie s used by sw ans a n d th e ir w ide ra n g e in th e w ilderness it w as n o t p ossible fo r g ro u n d-b o u n d o b serv ers to dev elo p a full p ic tu re o f sw an d istrib u tio n. In 1954 th e first w aterfow l b io lo g ist-p ilo t, H en ry A. H an se n , cam e to A lask a an d it w as im m ed iately obvious th a t sw ans, p e rh a p s m o re th a n any avian species, len d them selves to study fro m th e air. Sw an studies a re ju stified fo r th e ir ow n sa k e b u t also p ro v id e a h an d y in d ic a to r o f th e w ell-being o f all w aterfo w l in a given h a b ita t. W h en sw an p ro d u ctiv ity is low Cape Romanzof-A rc tic Slope Ne Ison Island Whistling Swan = Trumpeter Swan Y u k o n D e l t a Bristol Bay I 1 100 miles (161 km) Figure 1. A pproxim ate swan breeding range in Alaska.