per cent. These extremely low adult mortality rates 
the rather large number of nonbreeding birds wich liguesthatmececaae 
tive potential of the population. This adult mortality rate has a 
constancy which remains to be determined; it would result in an exceed- 
ingly long turnover period for cohorts numbering 1000 or more birds 
It is unfortunate that biologists unable to read Dutch cannot study 
Kortlandt's statistical treatment in detail. 
By obtaining population counts over a period of yea 
censusing banded birds in various colonies, anaes ansiveice sat Gee 
of banded birds, Kortlandt also concluded that band losses due to 
rings bending open amount to about 10 per cent. This figure, which 
includes extra mortality caused by "accidents with the bands." is 
the first correction factor to have been offered for this type of bias 
in survival studies. . 
Banding work in North America 
The relative success of double-crested cormorant banders in 
obtaining recoveries is illustrated in table lo. Among the 281 re- 
ports classified in this table as not used were 78 found dead during 
July or in cormorant colonies (nearly all of these the latter), 58 
reported merely as "found," 37 with no data as to how obtained, 28 
recorded as “probably shot," 25 "probably found dead," 2 vague as 
to how recovered, 15 skeletons or "remains," 7 with only the band 
and not the bird being found, 5 reported a year or more after actual 
recovery, ¢ with conflicting dates, 1 with the species questionahle, 
and 1 banding fatality. 
Table 16.-—-Variations in Recovery Rates for Double-crested 


cormorants 
| | Recoveries Effective Total 
Place of Dates of No. No. Not Recovery Recovery 
Banding Bander Banding Banded Used Used Rate V/ Rate e/ 
Kast Coast 
Quebec od. F. Lewis 1926-39 1076 7h 11 6.9 7.9 
Quebec H. H. Southam 1937-1 2800 228 3 8.1 9.7 
Maine Je M. Cadbury 1938-41 2035 99 28 4.9 6.2 
Maine Miscellaneous 1935-0 282 19 5 667 8.5 
Total 1926-41 6193 20 87 6.8 8.2 
Inland 7 
S. D. A. R. Lundquist 1929-37 1372 217 68 15.8 20.8 
Sask. F. G. Bard 1931-40 1928 268 87 13.9 18. 
Inland Miscelaneous 1928-40 1529 208 39 13.6 16.2 
Total 1928-h0 4829 693 19, 1b.b 18.u 
T7 this percentage is the number of recoveries used divided by the num- 
ber banded; it is called the "effective recovery rate" in this paper 
2/ this percentage covers both used and unused recoveries 
47 
