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Nesting

Nest Distribution. — On the Koenig study area we located 324 mallard, 316 gadwall, and 1,054 blue-winged teal nests useable for data analysis. Several of the cover types were represented by only 1 or 2 fields; thus, we were not able to test for duck nesting preferences. However, the large differences in duck nest densities calculated for the various cover types suggest strong hen selection for certain habitats. In 1976-78 before seeded nesting cover was available, odd areas had the highest mallard and gadwall nest densities (Table 4). Canal-side and roadside cover contained the next highest densities, and other cover types had low nest densities. Canal-side and odd areas also contained the highest blue-winged teal nest densities, but blue-winged teal also showed a preference for dry wetland.

In 1979-81, when seeded nesting cover became available, it ranked first in nest density ( = 58.7 nests/km²) for mallards and gadwalls. Odd areas, roadside, dry wetland, and canal-side had an average of 40.3, 38.7, 34.8, and 30.7 mallard and gadwall nests/km², respectively. Other cover types had low rates of use. The highest blue-winged teal nest densities were in dry wetland, canal-side, and roadside. Pasture had low nest densities, but it was important as it composed the largest area of nesting habitat and contained the largest number of nests (also see Duebbert et al. 1986).

In a comparison between habitat and duck nest densities we found a significant relationship (r = 0.89, 5 df, P = 0.02) between mallard nest densities (Table 4) and visual obstruction rating (Table 1) and a less significant (r = 0.74, 5 df, P = 0.09) relationship between gadwall nest densities and visual obstruction rating. There was no significant correlation (r = 0.67, 5 df, P = 0.14) between blue-winged teal nest densities and the visual obstruction rating.

Nest Site Selection. — The average distance between nest sites based on previous breeding success and age groups was significantly different (F = 5.13; 2, 20 df; P = 0.02) among mallards but not for gadwalls (F = 1.79; 2, 23 df; P = 0.19) (Table 5). Pair-wise comparisons of the mallard data indicated that the average distance between nest sites in 2 successive years of unsuccessful ASY mallards was greater than that of successful ASY mallards. No differences in distances between SY mallards and either category of ASY mallards were detected.

Table 5.   Comparison of characteristics of the last nest sites used by breeding mallards and gadwalls in year 1 to the first nest site of the subsequent year and a comparison of the natal nest site characteristics with the first nest of female progeny on the Koenig study area, North Dakota, 1976-81.
Species and nest measurement	Successful ASY hens	Unsuccessful ASY hens	First nest of female progeny
Mallard
n	8	5	10
(SE) distance (m) between nests	161 (61.6)	862 (316.4)	446 (90.1)
% in same cover type	100	80	60
% in same plant species	62	80	40
Gadwall
n	11	7	8
(SE) distance (m) between nests	249 (86.9)	831 (416.5)	699 (231.1)
% in same cover type	73	57	62
% in same plant species	54	43	25

Mallard and gadwall hens may reuse nest bowls of previous years (Duebbert et al. 1983). However, none of the marked hens on either study area returned to a previously used nest bowl.

Nesting Success and Breeding Success. — Mallard and gadwall nesting success overall was 11 and 10%, respectively. Mallard and gadwall nest success was significantly different among years (F = 9,75; 3, 52 df; P < 0.001) but not among cover types (F = 0.75; 5, 52 df; P = 0.59). In 1978, the year after the 1977 drought, nest success at 27% for mallards and 30% for gadwalls was well above the 6-year averages. Blue-winged teal nest success (23%) was over twice as high as mallard and gadwall success and did not differ among years (F = 1.86; 3,14 df; P = 0.18) or cover types (F = 1.17; 5, 14 df; P = 0.37). Hen success rates for mallards and gadwalls were estimated at 25% using a relation developed by Cowardin and Johnson (1979, Fig. 5) for converting nest success data to hen success.

We found no significant difference ( = 0.16, 2 df, P = 0.92) in the number of fully feathered (Class III) mallard young produced by hens of different ages (Table 6) or the percent of hens that nested. Hen age influenced recruitment in gadwalls, and we found significantly fewer nests ( = 6.45, 2 df, P = 0.04) and young ( = 9.17, 3 df, P = 0.03) produced by SY hens compared to ASY and ATY hens. Yearling hens contributed little to recruitment, and 28 known-age SY hens produced an average of only 0.20 fully feathered young/ hen.

Table 6.   Age-related productivity of known-age resident mallard and gadwall hens on the Koenig and Woodworth study areas, North Dakota, 1976-81.
Species and age	n	Hens with a known nest		No. of fully feathered younga	No. of fully feathered young/hen
		No.	%
Mallard
SY	41	27	66	59.4	1.45
ASY	22	12	54	39.2	1.78
ATY	11	5	45	13.0	1.18
Total or	74	44	59	111.6	1.51
Gadwall
SY	28	10	36	5.7	0.20
ASY	32	21	66	62.6	1.96
ATY	54	33	61	87.5	1.62
Total or	114	64	56	155.8	1.37
a In several instances where we lost sight of the hen and brood before the young were fully feathered, we estimated the number of young that would have reached the fully feathered age class.