
162 
WATERFOWL BREEDING GROUND SURVEY IN COLORADO, 1950 
Willard L. Flinn 
Introduction 
The 1950 waterfowl breeding ground study was conducted in the San Luis 
Valley and the South Platte River Valley, and the same methods and techniques were 
employed by the same men as in 1949. Aerial census of the San Luis Valley was also 
repeated to give a three-year comparison record. 
Techniques 
Ground work in the San Luis Valley was an intensive survey of selected 
nesting areas to determine total production by species and cover type, and decimating 
factors affecting production. Sample areas were selected on the basis of natural 
vegetation, water distribution, and general land use including crop production and 
grazing. Production was determined by periodical counts of nesting pairs, nests, 
and broods on the sample area. Ronald A. Ryder is credited with the work and data 
obtained from the San Luis Valley. 
The South Platte River Valley study was diviced into two parts. An extensive 
survey of 1,200 square miles was made, of which every twentieth Section was covered 
once, noting nesting pairs, broods, and lone birds, and where it was possible, by 
species. A smaller area of irrigated farm land, Township 7N, R68W, 6th Prime 
Meridian, was systematically covered six times during the period between June 13 
and August 21. Itis believed that data obtained is relative to very nearly the total 
waterfowl production of the sample area. This study is credited to Jack R. Grieb, 
Colorado Cooperative Wildlife Research Unit, Colorado A, & M. College. 
The aerial work in the San Luis Valley was done during the latter part of 
June, at a time when it was believed that most broods were present. The area was 
arbitrarily outlined and divided into five parts, each having characteristic habitat 
and land use; the total having an area of 1,484.5 square miles. Transects were 
flown to cover approximately 4.3 percent of the farm and meadow land (1,310 square 
miles) and total counts were made on the remaining 174 square miles. Information 
obtained by aerial census is credited to Kenneth B. Milyard and Clyde Matteson. 
Weather 
These areas of Colorado, where waterfowl breeding studies were conducted, 
were dry during the breeding season as compared with 1949, and probably were drier 
than normal. Many small water holes, usually providing good nesting cover, were 
dry or drastically reduced. The total acreage of surface water in the San Luis Valley 
was considerably less than last season, probably causing a concentration of ducks on 
the permanent bodies of water, such as the Russell Lakes study area. The same may 
be said for the South Platte Valley, where most of the available nesting area was 
confined to a strip near the river. 
Findings 
San Luis Valley Study Area 
Nesting pairs were much more abundant on the study areas than last year. 
This season, final data for 370 mallard nests (2,599 eggs) was obtained, as compared 
