this departure from reality is certainly not mch greater than in 
modern tables set up for a standard million persons. One can then 
claim that all 141 persons were exposed to the risk of death at the 
earliest age interval in the life table and proceed as Pearson did 
to compute mortality rates and expectations of further life. 
When banded birds are recovered dead by the general public 
and reported to a central office, the mortality may be spread over 
many years just as the original dates of banding are. Lack (19l3a, 
1943b) was the first to take such mortality records and form a life 
table. The method seems similar to Pearson's (1902), and the results 
can be regarded as dynamic life-table analyses for hypothetical popu- 
lations. In subsequent parts of the present report, this technique 
will be referred to as Lack's method. 
Composite life tables have also been set up using a time- 
specific analysis instead. In these, mortality reports of banded 
birds have been grouped with survival reports to form life curves 
for the lapwing (Kraak, Rinkel, and Hoogerheide 19,0), the European 
sparrow. hawk (L. Tingergen 1946), and several other birds. This 
aggregation of mortality and survival will not yield reliable 
estimates of mortality rates that change with age (Chapter III). 
Nice (1937), Lack (op. cit.), Farner (1945), and others have shown, 
however, that in adult birds the mortality rate is reasonably con- 
stant for all ages. In such cases the method is a permissable one. 
Its limitations will be further discussed in a later chapter, and 
an example worked out solely from mortality reports is given in 
table l. 

larne Fisher (1922, 1925) has claimed that it is possible to construct 
a human mortality table from a collection of death certificates and 
with no knowledge of the number of lives exposed to risk at various 
ages. His principal working hypotheses appear to have no present 
application in ornithological studies, and his attempt to reconstruct 
a time-specific life table from limited data has been coldly received 
by American mthematicians. In fact, one commentator at a Toronto 
meeting of the International Mathematical Congress made the very 
positive statement that any satisfactory results from Fisher's 
method would be due solely to the effect of pure chance. 
