POPULATION DYNAMICS OF DUCKS AND GEESE 



89 



Table I.— Estimates of the mean anmial survival rates of adult wildfowl 



Only one estimate is given for each form (species or subspecies): where several mde- 

 pendent estimates were available a mean value has been used. Standard deviations are 

 given wherever the method of estimation permits their calculation. All estimates are 

 based on recoveries of marked birds, except those marked *, derived from censuses and 

 age-ratios. 



Adult survival-rate 



Form 

 Tribe Anserini 



Anser hrachyrhynchus 

 A. a. albifrons . 

 A. a. flavirostris . 

 A. a. aitser 

 A. c. caerulescens* 



A. c. atlatiticus* . 

 Branta c. canadensis 



B. c. moffitti* . 

 B. b. bemicla* . 

 B. b. hrota 

 B. b. orientalis , 



Tribe Tadomini 

 Tadorna tadorna 



Tribe Anatini 

 Anas a. acuta 

 A. crecca crecca . 

 A. crecca carolinensis 

 A. p. platyrhynchos 

 A. rubripes 

 A. penelope 

 A. d. di SCOTS 

 A. clypeata 



Tribe Somateriini 



Somateria m. moUissima 



Tribe Aythyini 



Aythya vallisneria 

 A. americana 

 A.fuligula 

 A. m. marila 



Tribe Cairinini 

 Aix sponsa 



Tribe Mergini 



Melanitta n. nigra 

 Clangnla hyemalis 

 Mergiis m. merganser 



Regional population 



0-64 



o-77±o-04 

 o-72±o-04 

 o-6o±o-07 



Ohio. 



Iceland. 



British- wintering. 



background for the study of exploitation, which in Europe and North 

 America consists almost entirely of the shooting of full-grown ducks and 

 geese for sport. (It is of interest to note that pubhc opinion, and legislation, 

 in most countries is hardening against the commercial use of wildfowl, so 

 far as this amounts to offering the killed birds for sale.) The motives of sports- 



