Table 5.—Onset of Illegibility in Bird Bands 
This table summarizes the years of use represented by illegible 
bands that the Fish and Wildlife Service had to etch with acid 
in 1946 and 1947. The illegibility was generally brought about 
by the environment; some bands, however, had been mutilated by 
gunfire; others were mutilated in the act of being flattened 
out for mailing 
_ Usual Frequency by Years of Use 
Species Band 
Size 1 23 &§ S 6 7 8 9 10 11 12 13 1y Total 
De-c. Cormorant 3 
Canada Goose 
White Pelican 
Mallard 
Black Duck 
Pintail 
Canvas-back 
Ring-necked Duck 
Redhead 
Lesser Scaup 
Herring Gull 
Coot 
Gadwall 
Green-wed. Teal 
T. 
Summary 
j At the present time, the difficulties of compiling acourate 
survival data for each stage of a bird's life encourage the synthetic 
construction of life tables based upon data obtained from diverse : 
sources. Even when based on real conditions encountered in the field, 
survival statistics represent theoretical populations when means 
(averages) are computed. The survival of young birds after they leave 
the nest currently presents the greatest difficulty in the measurement 
of mortality. Contrary to recommendations by Lack (19l6b) and Farner 
(19147), banding analyses of survival in the northern hemisphere should 
start not as of January 1 but as close to the fledgling period as the 
data permit. . 
~ 
~ 
~~ 
PirerlrirPtii naooilii 
~ 
Bern 
27 
4S 
pr erprperevrereoepwns 
tr>rierrtrirPnerirei 
rer iowrtwmmata 
(= 
mH Mm © 
PRP tiePrPirorwliit 
per er ett wernt 
rst prtroertwretrwntns 
erpeeeneewmt @eusn 
9 ttPeboap_vuproeee 
tererprrwestprwetus 
ptterrtivumreteeuee 
aoreutpueveveevu_etees 
sr trtrwpPorevetuurnaea 
VI RXAANAAADNAH OO OW- O 
tet went 
=) 
MMH HO eH bt 

Retrapping of adult birds tends to give minimal estimates of 
survival because of (1) individuals shifting their residence after 
nesting calamities (here estimated as 7 per cent of the song sparrows 
studied by Nice), or (2) homing failure, or (3) inefficiencies in the 
trapping technique. Under certain conditions correction: factors for 
these sampling errors can be worked out. 
The centralized banding files of the Fish and Wildlife 
Service, used in this study, were carefully scrutinized for weaknesses. 
25 
