Mallard Recruitment in the Agricultural Environment of North Dakota

Nest Initiation

The date when nest initiation begins and the duration of the nesting effort are important for waterfowl because hen success is a function of nest success and renesting rate. The nest initiation curves for the 4 years are similar except for 1979, a particularly cold year, when nesting was late (Fig. 3). We therefore examined the relation between the median nest initiation date and April and May temperatures (Fig. 4). Both regressions, although based on small samples, were significant. The average temperature in April, when most of the birds arrived, appears to delay the peak of nesting activity 2.23 days for a drop of 1°C. Hammond and Johnson (in press) reported a 0.99-day delay of the peak in nesting activity per drop of 1°C in temperature. There was no evidence of a relation between temperature and length of the nesting season (Table 3).

GIF-Median nest initiation date and mean monthly temperature

Table 3. Relation between mean April and May temperature, median nest initiation date, and season length for mallards in central North Dakota.
Year N Median initiation date^a Temperature (C) 90% quantile 10% quantile Season length

Apr May

1977 16 133.0 9.22 16.91 164.1 115.8 48.3

1978 36 137.0 5.17 14.11 153.1 104.9 48.2

1979 42 156.5 -0.72 8.39 172.7 123.0 49.7

1980 45 135.0 9.11 15.39 164.4 112.2 52.2

^aJulian day.

**Table 3.** Relation between mean April and May temperature, median nest initiation date, and season length for mallards in central North Dakota.
Year	N	Median initiation date^a	Temperature (C)	90% quantile	10% quantile	Season length
Apr	May
1977	16	133.0	9.22	16.91	164.1	115.8	48.3
1978	36	137.0	5.17	14.11	153.1	104.9	48.2
1979	42	156.5	-0.72	8.39	172.7	123.0	49.7
1980	45	135.0	9.11	15.39	164.4	112.2	52.2
^aJulian day.

We were unable to detect a difference in median nest initiation date between SY and ASY nesters (Table 4). Coulter and Miller (1968) and Dzubin and Gollop (1972) suggested that older hens nest earlier than young hens. Older birds may nest earlier than young hens; however, our sample of nests was not sufficient to demonstrate the difference. Batt and Prince (1979) demonstrated that there is considerable genetic variation among females in the date of first nesting in penned birds. This variation undoubtedly adds to the difficulty of demonstrating age-related differences in nest initiation date. Batt and Prince (1978) also failed to demonstrate a difference in nest initiation between ages, but their captive birds were fed ad libitum and the hens did not have to compete for resources.

**Table 4.** Median nest initiation dates for SY^a and ASY^b mallards nesting in North Dakota during 1977-80.
Year	SY		ASY
Year	N	Julian day	N	Julian day
1977	4	132	12	133
1978	8	135	26	138
1979	7	157	23	151
1980	13	135	31	132
^aSecond-year hens in first year of nesting. ^bAfter-second-year hens in their second or later nesting years.

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