The census results prompted Unit.personnel to return in late May 
and retrap 63 sites on Prescott peninsula which had been trapped in 
April. The results of this have been discussed under the section on 
movements, but the 8 new birds caught on sites holding other birds in 
April would suggest one of three possibilities: either the original 
occupants had migrated north, shifted their singing territory, or 
suffered mortality. The latter possibility appears remote in the light 
of observations on spring mortality. 
In two of the 8 sites where new birds were taken late in May the 
original occupant was also caught in a dawn flight indicating two birds 
in each case were using the singing ground or closely adjacent ones 
late in the breeding season. Three of the sites holding new birds had 
taken three birds banded in 1950 during April and therefore, presumed to 
be residents. One of these 3 sites had caught a third bird in late March 
which was unaccounted for in the late May retrapping. The remaining 3 
sites which yielded new birds in May had taken April birds on April 10, 
April 17, and April 18 respectively. Only one, therefore, had taken a 
bird during the height of the migration. 
In summary, analysis of these few returns points to a shift of 
singing grounds in most instances. Two of the birds caught in April 
may have been migrants but this is unlikely for the ones caught April 
17 and 18. In addition, bird #50-3019 had been banded April 25 and was 
recaptured May 16, 1 1/3 miles north of his April singing site. These 
new captures lend inconclusive evidence to the theory that a late wave 
-of birds came in during late April or early May as the census results 
suggest. During the late retrapping, two additional new birds were 
caught on sites not occupied in April. 
Tf there is any truth in the theory of a second migratory wave 
the origin of these late birds is difficult to explain. Another pos- 
sibility is that there is more than one height of breeding activity 
during the spring. All data are insufficient to be significant. 
Counting Singing Males as a Census Method 
The behavior of breeding males as revealed by trapping may help in 
amore accurate interpretation of the results of the annual census counts 
on singing birds. Other investigators have reported males shifting sing- 
ing grounds during the spring. How such an assumption is arrived at has 
not been clearly described. Without knowing the identity of individual 
birds it would seem difficult to be sure of such a behavior pattern. 
Results of trapping demonstrate that many individuals do shift singing 
grounds, but this was not apparent in census runs since all recaptured 
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