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Mallard Recruitment in the Agricultural Environment of North Dakota

Cause of Nest Loss

Predation was by far the most important cause of nest failure. It accounted for nearly 70% of the unsuccessful nests and probably was a factor in loss of nests to abandonment and unknown causes (Table 11). Abandoned nests frequently had eggs disappear between the first and second visits. Klett and Johnson (1982) suggested that Franklin's ground squirrel (Spermophilus franklinii) may have been responsible for egg loss. Perhaps disturbance by ground squirrels also causes abandonment. Other abandoned nests were uncovered, which suggests that the hen may have been flushed by a predator thus causing her to abandon the nest. If the hen was never seen after abandonment, she may have been killed and removed from the nest. We were unable to determine the cause of loss of 8 nests, either because it was not possible to distinguish among predation, weather, and machine destruction or we were unable to relocate the nest even though we knew it was unsuccessful from telemetry data. We were unable to identify the predator responsible for nest destruction in 77% of the predator-destroyed nests examined. Even for those nests where the appearance of the nest and shell fragments closely resembled published descriptions (Rearden 1951, Einarsen 1956), we felt that the evidence was not conclusive. We relied on strong circumstantial evidence such as observation of the predator or its tracks or recovery of the hen from a den.

**Table 11.** Fate of 129 nests of radio equipped mallard hens in central North Dakota.
Class		Year
		1977	1978	1979	1980	All years
		1977	1978	1979	1980	N	%^a
Successful		3	11	8	8	30	23.3
Unsuccessful		14	23	29	33	99	76.7
Abandoned		0	1	7	3	11	11.1
Predator destruction		11	19	15	24	69	69.7
	Skunk	1	2	1	3	7	10.1
	Raccoon	1	0	0	1	2	2.9
	Ground squirrel	1	0	0	0	1	1.4
	Fox	1	1	2	1	5	7.2
	Mustelid	0	0	0	1	1	1.4
	Unknown predator	7	16	12	18	53	76.8
Other destruction		3	3	7	6	19	19.2
	Machine	2	2	2	2	8	42.2
	Livestock	1	1	0	0	2	10.5
	Weather	0	0	0	1	1	5.3
	Unknown	0	0	5	3	8	42.2
Total^b		17	34	37	41	129	100.0
^aShown as percent of subcategory. ^bDoes not include nests where observer caused abandonment or nests where the fate was unknown.

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