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COMPARISON OF AIR AND GROUND WATERFOWL COUNTS ON IRRIGATED LAND 
IN NORTH-CENTRAL COLORADO 
1951, 1952 and 1953 
Jack R. Grieb 
Introduction 
The final results of this 3-year study are given in summary form. The same 
study area and methods used during past years were retained again in 1953 to 
determine, principally, whether the air-to-ground ratio varies between years for 
the same observer. A complete description of area and methods is given in 
Waterfowl Populations and Breeding Conditions, Summer 1952. 
Results 
Aerial breeding-pair counts in the Fort Collins area are best taken during late 
April, May, and early June for it is during this time that most territories are still 
active. The total counts of territories, by coverage, for 1951, 1952 and 1953 are 
tabulated in Table I, This table also lists the air-to-ground ratio for each coverage, 
and gives the result of the chi-square test. Thus, it was determined that average 
air-to-ground ratios found each year were consistent, being 2.23 for 1951, 1.52 for 
1952, and 1.43 for 1953. Since the 1952 and 1953 study was conducted by the same 
observer, then it was desired to test whether a significant difference exists between 
ratios for the same observer between years. This was done by the "'t'"' test comparing 
the 1952 average (1.52) with that of 1953 (1.43) resulting in t=.728, t .01 =3.707 
(6 degrees of freedom). Thus, there was no significant difference between counts 
made by the same observer for the two years. Combining the two year ratios gives 
an average ratio of 1.49 which can be used in correcting breeding~-pair counts for 
this particular observer. The difference between the 1951 and 1952-53 ratios were 
caused by using different air observers. | 
The various habitat types were further analyzed to determine whether individual 
types also had a consistent ratio. This analysis revealed that 4 types were consistent 
in 1951 and 6 types were consistent for 1952 and 1953 combined (Table II). Therefore, 
on those types wherein the ratio was found to be consistent it would be possible, given 
the same observer, to multiply the results of an air coverage of a given type by the 
ratio for that type to obtain an estimate of the ground count. 
As can be noted in Table II, the ratio not only varies in size between the two 
years, but also some types which were consistent one year were not the next. This 
can be attributed to the difference in observers. 
The general trend for all three years of study was that aerial counting was 
easier on those areas where high-growing vegetation was not present to interfere with 
the observations (small lakes and ponds, large lakes, irrigation canals and irrigation 
ditches); and most difficult on the habitats with heavy permanent cover (creeks and 
drains, river and sloughs). 
