PART I. CRITIQUE ON METHODS 
Chapter I.--Anatomy and Basis of Life Tables 
This report is an exploration into the population dynamics 
of ten North American birds. The basic materials are literature on 
the productivity of these species and survival records maintained in 
the banding files of the United States Fish and Wildlife Service. 
Because the use of life tables in ornithology is still relatively 
new, the present study reviews the assumptions underlying such 
analyses--then proceeds to balance our present knowledge of productivity 
against the availability of mortality data on representatives of eight 
orders of birds. All too often, the samples finally proved to be too 
small, but the mallard does offer a rapidly increasing wealth of data 
for the student of vital statistics. In the case of this species, I 
hope this report will demonstrate the wide variety of indices into 
which modern banding data can be converted, 
The present study is an ecological one, not a statistical 
treatise. No attempt has been made, for instance, to allocate sampling 
errors in such matters as the computation of seasonal recovery rates 
or to devise tests of significance for differences between some of 
the complex mortality series obtained from banding records. These 
still invite special studies. Despite their omission here, the report 
that follows is not an easy one to read, at least for biologists. For 
years, ornithologists have been compiling statistics on the numbers 
of eggs in birds' nests, on the percentages of successful nests, on 
the number of young per brood, and on the ages at which individual 
birds die. To interrelate these into crude but meaningful life equa- 
tions for the best~-studied species now requires effort and diligence. 
It is my conviction that these new pathways of the mind will in time 
lead us to broad vistas where multitudes of formerly unrelated facts. 
will at last merge into logical perspectives, and the struggle for 
existence by each species will be more clearly visible. One such 
pathway is traversed here. The clearing away of boulders will, I 
hope, make it easier for others to follow, 
History 
The term life tables can be applied to tabulations of popula- 
tions according to age groups. These summaries of the age structure 
of various species suggest to the geneticist and the evolutionist the 
rate to which natural selection may cull out mtations or permit them 
to become predominant. To medical men, life tables often disclose 
advances and weaknesses in public-health programs. From them ecologists 
can gauge environmental forces, fisheries workers can estimate future 
catches, and game managers appraise productivity and hunting regula=- 
tions. Ina real sense, they bridge the gap between the older biology 
and the new. 

