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Mallard Recruitment in the Agricultural Environment of North Dakota

Habitat Characteristics in the Vicinity of the Nest

A number of wetland characteristics were measured at each nest site within 200 m of the nest and within 1 km of each nest (Table 12). These characteristics were compared for successful and unsuccessful nests. Density of wetland basins was 11.1/km2 within 1 km of the nests and 13.5/km2 within 200 m of the nest. The Coteau portion of the study area that contained all nests had a wetland density of 13.0 basins/km2 (Cowardin et al. 1981). The similar density of wetlands at nest sites and in the region agrees with the habitat preference analysis (Table 8) that showed no significant preference for wetland habitat for nesting.

Table 12. Selected habitat characteristics near mallard nests in central North Dakota.
Successful nests Unsuccessful nests
N = 110 SE N = 30 SE
Wet basins within 200 m at initiation 2.1 0.34 1.6 0.18
Wet basins within 200 m at hatcha 2.0 0.41 1.3 0.15
Distance to nearest water at initiation (m) 141.7 33.6 211.6 26.6
Distance to nearest water at hatch (m) 160.5 36.1 263.9 30.8
Distance to travel lanes (m) 56.7 16.3 59.3 8.6
Distance to buildings (m) 1,026.2 129.5 1,030.0 55.0
aSignificant difference between successful and unsuccessful nests (P < 0.05) by ANOVA. All other   differences nonsignificant.

To further examine the relation between nests and wetlands, we determined the distance to the nearest wetland basin containing water at initiation and at hatch. We also determined the number of basins and parts of basins containing water within 200 m of the nest at hatch and initiation. The number of basins within the circles cannot be expanded to estimate total wet basins on the study area because inclusion of parts of basins in the circle would result in an overestimate of density. We measured 2 habitat characteristics that might influence predator activity and nest success. These were distance to travel lanes such as roads, fencerows, and wetland margins and distance to buildings that might be used by predators.

All of the factors in Table 12 were tested among years and between successful and unsuccessful nests by separate analyses of variance. As might be expected, there were significant year-to-year differences. There was also a significant difference in the number of wet basins at hatch between successful and unsuccessful nests, which suggests that nests were more successful where they were in habitat with an abundance of ponds retaining water well into the nesting season. This result could have a biological basis that we cannot explain or it may merely reflect high density of semipermanent wetlands in hilly, rolling country where nesting cover is generally better than in flat, easily plowed country.

Livezey (1981b) also investigated the relation between nest success and distance to water. His sample contained 92% blue-winged teal (Anas discors) nests and only 5% mallard nests. His data suggest that nests for all species combined were less successful near water than those far from water. The conflicting results might be explained by regional differences in composition, abundance, and behavior of the predator community, as well as different biology between teal and mallards.

Kirsch et al. (1978) demonstrated that habitats with tall dense cover had higher success than habitats with sparse cover. Livezey (1981a) reported similar findings in a study of the effect of cover height and density on nest success in Wisconsin. We made similar measurements of visual obstruction at all nests and also found significantly greater visual obstruction (at a height of 58 cm) for successful nests than unsuccessful nests (at a height of 38 cm).

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