POPULATION DYNAMICS AND THE EXPLOITATION OF 

 DUCKS AND GEESE 



H. Boyd 



Wildfowl Trust, Slimbridge, Goucestershire 



The family Anatidae, comprising about 145 species, is of world-wide 

 distribution, but statistical information is limited almost entirely to species 

 living in the Arctic and temperate regions of Europe and North America. 

 The family is by taxonomic standards a homogeneous one in which current 

 opinion favours the recognition of relatively few genera, and the geographical 

 limits of the sample restrict attention to the occupants of a small range of 

 habitats. Thus a comparative study of present knowledge of the dynamics 

 of different species might be expected to reveal similarities rather than 

 differences. In the first section of this paper I assemble information about the 

 fecundity and survival to maturity of twenty populations of fourteen species. 

 A second section is devoted to estimates of the mean adult survival rate of 

 populations of twenty-three species. The third section discusses specific 

 studies of the relation between the kill by man and losses from other causes 

 against this comparative background. 



THE PRODUCTION OF YOUNG BIRDS AND THEIR SURVIVAL 



TO MATUPJTY 



In comparing specific characteristics of fertility and survival it is desirable to 

 restrict attention to populations which are in a steady state. So few long and 

 intensive studies of wildfowl populations have been made that it is impractic- 

 able to set up very rigorous criteria for selection. The results used here have 

 been obtained from studies during at least three years of entire specific or 

 subspecific populations or of breeding groups in clearly-defmed areas, and 

 are hmited to breeding populations which varied very Uttle in size, or if 

 they fluctuated more widely showed no upward or downward trend. 



The most economical method I could fmd of presenting the information 

 is the series of histograms in Fig. i, which record average annual production 

 by a hypothetical group of 100 mature females from each population. The 

 average number of eggs actually laid is substantially less than the number 

 expected on the hypothesis that the output is equal to (mean clutch size X 100) 



