















Bach route is checked once between May 20 and June 10. Intensive 
studies in the eastern United States (Foote and Peters, 1952) indicateg 
that dove calling is relatively stable during this period. Call-count 
surveys are not made when wind velocities exceed 12 miles per hour or 
when it is raining. 
Records are kept of all doves seen or heard calling along the 
routes. The numbers heard calling during the 3-minute listening perioge 
are totaled for each route to provide the data for determining the popu- 
lation index. The numbers of calls per dove and of doves seen are not 
currently used in the index calculation, but they are recorded. A j 
detailed analysis of these and other pertinent data from past call coynte 
is currently under study by the Migratory Bird Populations Station. 
Studies by Frankel and Baskett (1961) and Jackson and Baskett (196k) 
have shown that unmated males call at a greater rate than mated males. 
This suggests that the reliability of the annual call-count census is 
reduced by the variability in the ratio of mated to unmated males. H 
ever, Wight (1964) observed that variations in the ratio of mated to 
unmated males, where the adult sex ratio approached equality, did not 
significantly alter the reliability of the dove call count for measuring 
annual trends of breeding mourning doves. Irby (1964) also found no 
evidence on his study area in Arizona that the numbers of unmated males 
materially affected call-count results. 
Quality checks of field data 
Survey reports were examined to determine circumstances affecting 
the accuracy with which the routes were run and the data recorded. 
Records for routes run under unacceptable conditions were not analyzed. 
Reports on routes completed under the prescribed conditions but con- 
taining discrepancies or errors, or lacking data, were examined to 
ascertain whether parts were acceptable. If so, they were used in 
analyses for which they were applicable. Where there was a change in 
observers on a route from one year to the next, the data were examined 
to determine whether an unexpected population change was apparent. When 
such differences exceeded those of the prescribed limits, they were 
attributed to differences in observers, and the data were not used in 
the current analyses. 
