171 
Table II. - Air-to-Ground Comparison by Habitat Types, 1951 compared to 
1952 and 1953 
Average Ratio Chi-Square Calculations 
Ground to Air 

Habitat T - 
MELEE 1951 1952-53 ee aS Ss Bi sf 
x KX .5(2 DF) xX x .5(7 DF) 
Large Lakes 2.36 1.48 712% 1.386 14,15 6. 346 
Small Lakes and 
Ponds 1.82 . 96 -922* 1,386 6.274% 6.346 
Irrigation Canals 1.36 1.35 . 838% 1. 386 4.797% 6,346 
Irrigation Ditches 2.30 1,54 197% 1.386 4.254% 4,351 (5 DF) 
Rivers 5.27 1.80 aK mK 1, 875% 6,346 
Creeks and Drains ae 2.09 ak we 926% 2.366 (3 DF) 
Sloughs 2.96 2.25 1.932 1.386 5. 988* 6. 346 
* Indicates a good fit -- average ratio can be applied. 
** Insufficient data, 
Sources of Variation between 1951 and 1952-53 

As mentioned previously, the air-to-ground ratio differed between 1951 and 
1952-53. This was apparently caused by using a different observer for each of the 
two trials. The first year all aerial observing was done by the writer, while the 
second and third year counts were made by Erwin L. Boeker. The writer had 
previously done no aerial counting of waterfowl, and had very little flying experience. 
Mr. Boeker, on the other hand, was a capable pilot with experience in aerial census. 
Obviously, experience is one of the prime factors in the differences between the ratios 
obtained for each year. 
It is possible to point out where experience helps in counting. By referring to 
Table II, it may be seen that without exception Mr. Boeker's air-to-ground ratio 
was much smaller than the writer's for each habitat type. However, the differences 
were larger on those types with heavy cover as river, and creeks and drains, Therefore, 
it is possible to conclude that an experienced observer will see an even greater percent 
of birds on those types with dense cover than will an inexperienced observer, 
Experience also plays an important part in observing all species of ducks. This 
is emphasized by Table III, which shows the percent of ground-counted species seen 
from the air. Although the difference between mallard-like ducks was not great for the 
three years, only 8 percent of the teals were observed in 1951 as compared to 59 percent 
in 1952, and 58 percent in 1953. 
