may occur, or (3) an obscuring interaction between phenology in 
various portions of the survey area and timing of the survey. 
Reason 3 will be discussed further in another section of this 
report. 
As a third method of distributing data, 75 contiguous degree 
blocks were arbitrarily grouped by 4 different methods into 5 
units of 15 blocks each. Counts for the 4 years in these larger 
units were examined using an analysis of variance to separate 
differences due to years from differences due to areas. 
Analysis of variance showed a significantly high variance 
ratio for each arrangement except one. The highest variance ratio 
(F = 4.31 with 4 and 12 degrees of freedom) was obtained from the 
third pattern (fig. 3). 
These analyses suggest that highest counts of black ducks have 
been obtained from the west-central portion of the area surveyed, 
an area lying about one-third of the distance from the Great Lakes 
to James Bay. Evans (1956), from study of the distribution of 
aerially observed breeding populations (all species) in northeastern 
Canada between 1952 and 1956, suggested that higher counts of birds 
in a zone north of the Great Lakes were due to "pile-up," a stall 
in migrational movement caused by unsuitable climatic conditions 
further north. 
Establishing the Phenology of the Nesting Cycle 
The likelihood of observing black ducks from aircraft and the 
frequency of the various group-sizes in which black ducks occur are 
probably related to the phenology of the area. Early in the spring 
there may be a high occurrence of flocked black ducks that are 
migrating northward or are "piled-up" and waiting for milder weather 
before continuing northward. Wright (1954) described the spring 
flight of blacks to a New Brunswick study area as an arrival mainly 
in pairs. About 2 weeks after the arrival of the first pairs, a 
"wave" of unpaired blacks passed through. Stotts and Davis (1960) 
indicated that in Maryland the peak period of pairing of blacks 
occurred in December and January. Consideration of these obser¬ 
vations would suggest that counts showing a high frequency of pairs 
and flocks relate to an early stage in the nesting season for the 
area surveyed. 
As the nesting season progresses, the female becomes increasingly 
attached to the nest site, flushes less readily, and flies shorter 
distances when startled (Stotts and Davis, I960). Thus, the obser¬ 
vation of lone males on territory should predominate in aerial counts 
5 
