Before 1966, the BDI for each State represented the average number 
of birds heard calling per route within that State, thus weighting ai] 
routes equally. The State averages were then weighted in proportion ¢; 
the estimated area of dove habitat in each State of a management unit 
(fig. 2) to provide a Breeding Population Index for each unit (U.S. 
Bureau of Sport Fisheries and Wildlife, 1957). 
Beginning with the 1966 survey, weighting factors based on physio- 
graphic regions were used for calculating BDI values in States which 
had been "randomized" for 2 or more years. The average number of doves 
heard calling per route in each region within a State was weighted by 
the percentage of the total land area in the State occupied by that 
region. 
Calculation of management unit BDI's since 1965 has involved two 
similar procedures as a result of a computer program change. In 1966 
and 1967, indexes were determined for each management unit by weight- 
ing each State's BDI by the percentage of the total land area occupied 
by that State in the management unit. When a region within a State was 
not represented by a BDI, that region assumed the mean of the other 
regions weighted by land area in that State. Starting in 1968, manage- 
ment unit BDI's were derived directly from State physiographic region 
BDI's. When a region within a State was not represented by a BDI, that 
region assumed the weighted management unit mean. Differences between 
these procedures are evident only when physiographic regions within 
States are not represented by comparable routes. 
Random routes in Maine, New Hampshire, Rhode Island, and Vermont 
were established after initiation of a special study in 1966 to deter- 
mine the effects of hunting regulations on dove populations in the 
Eastern Management Unit. In order to preserve the experimental design 
of the special study, call-count data from these States have not been 
included in the Eastern Management Unit means. Consequently, the 1970 
and 1971 management unit means were derived from comparable routes run 
in 44 States. 
Determination of short-term population changes, 1970 to 1971 
Changes in the size of mourning dove breeding populations within 
States are indicated by data from 690 comparable routes run in both 
1970 and 1971. Weighted average BDI values for each year are presented 
by States within management units (table 1). Differences in these BDI 
values, expressed as percent change, determined the magnitude of change 
in each State's breeding population. Changes in management unit popula 
tion levels between 1970 and 1971 are derived from weighted State value 
(table 3). 

