The initial size of ‘mallard egg sets, the percentage of 
hens renesting, the percentage of success in each attempt are field 
statistics that are unavailable at the time of this writing. One 
can ask, "Would a mean clutch of 7.8 eggs suffice to balance a mal- 
lard population?" This can be studied by calculating what happens 
when only one nesting attempt is made by 100 pairs in a given breed- 
ing season (table 66). 
. Table 66.-<Dynamios of a Hypothetical Mallard Population 
(a) 100 pairs lay clutches averaging 7.8 (table 2h) 780 eggs - 
(b) 55% of these (table 2);) hatch as broods of 7.6 
(table 26) | - 18 young 
(c) about 30% of these “(274 in Chapter 12) die by | 
Sept 1. This leaves: - = 293 -« 
(d) about 324% of the remaining survive one more 
year (table 28): | - - = 9h, 
(e) 100 pairs represent 200 birds at start of. nesting 200 
(f) 90% (this is a guess) survive to September 1 - - 380 - 
(g) 51.3% (this chapter) survive one more year - -- 
(h) Total | 186 
Readers who have followed the mallards accounts thus far set 
forth in this report will recognize that many of the statistics used 
in this tabulation are crude ones. We do have here, I think, all the 
pertinent productivity and mortality data available as of 1918. In 
the rough picture of population dynamics in this species emerging 
at this point, we see that the 186 survivors on the final September 1 
(line h) are approximately the same in number as the 180 adults alive 
one year earlier (line f). The general statistics roughly approach that 
of a stable population. The present evidence thus points to a mean 
clutch of 7.8 as sufficient to balance mallard populations. Since it 
is apparent, as Sowls (in litt.) points out, that initial clutches 
of this species average much larger (10 or 11), it would seem that 
renesting is commonly resorted to in this species. Although its 
statistical dimensions still remain blurred, the picture sensibly 
agrees with that of a persistently early-nesting species which has 
ample time to renest annually (Hochbaum 1°)5). 
It therefore seems best at this time to reject the idea — 
that mallards have smaller clutches than redheads and that they | 
overcome this handicap by achieving a higher percentage of nesting 
success, The two species appear to lay sets with about the same 
number of eggs. The mallard lays earlier, and it appears to do so 
for a good reason. 
158 
