Long-term Trends 
For the purpose of showing long-term trends in the breeding-popula- 
tion index of a State, a base year was selected, and annual percentage 
changes have been applied to the base figure (average doves heard calling 
per route) to give an adjusted figure which shows the true relation of 
indexes from year to year. The selection of a base figure is necessary 
because not all routes are censused each year. From a base year, average 
doves heard calling per route for each State has been adjusted annually 
according to the percentage change from the preceding year in counts on 
comparable routes. For example, the base year for Alabama is 1957 
(table 3). In that year, the average doves heard calling per route was 
21.1. In 1958, the percentage change from 1957 in counts on comparable 
routes was an increase of 12.8 percent, so the base figure of 21.1 was 
adjusted upward by 12.8 percent to a level of 23.8. In 1959, the per- 
centage change from 1958 in counts on comparable routes was a decrease 
of 21.6 percent, so the 1958 adjusted figure or adjusted base was 
decreased by 21.6 percent, from 23.8 to 18.7. For the current year, 
1961, the percentage change from the preceding year in counts on compara- 
ble routes was a decrease of 11.5 percent, which decreases the 1960 
adjusted figure from 22.7 to its 1961 level of 20.1. 
TRENDS IN THE BREEDING-POPULATION INDEX - 1961 
Eastern Management Unit (fig. 1) 
The breeding-population index for the Eastern Unit decreased 4 per- 
cent from the 1960 level (table 1). Figure 2 shows that the breeding 
index of the Eastern Unit has been increasing generally over the 7-year 
period prior to 1961. The slight decline in 1961 placed the population 
index 31 percent above the 1953 level. 
In hunting States of ‘the Eastern Unit, the breeding index decreased 
6 percent from 1960 but remained 36 percent above the 1953 level (table 1 
and fig. 3). In nonhunting States, the index increased 5 percent from 
1960 to 1961 (table 1). The long-term trend of the breeding index in 
nonhunting States of the Eastern Unit is shown in figure 3 and indicates 
a relatively stable population in recent years. The 1961 index, however, 
was 18 percent above 1953. 
Central Management Unit (fig. 1) 
The breeding-population index for the Central Unit decreased 10 
percent from the 1960 level (table 1). Figure 2 shows that for 6 years 
during an 8-year span the breeding index of the Central Unit increased, 
and the downward trend in 1961 left the index 52 percent above the 1953 
Level. 
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