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Temporal Flexibility of Reproduction in
Temperate-breeding Dabbling Ducks

Results


Interspecific differences in nesting intervals during spring. — Mallards and Northern Pintails (hereafter pintails) nested first and Gadwalls nested last (Fig. 1). Nesting was completed first by Northern Shovelers (hereafter shovelers) and pintails followed by Mallards and Blue-winged Teal and then Gadwalls (Table 1). Shovelers initiated nesting third (Fig. 1) but were the first to complete 50% of nest initiations (Table 1). Pintails began nesting about two weeks earlier than shovelers (Fig. 1) and terminated nesting on a schedule slightly behind shovelers (Table 1). Interspecific differences in length of nesting was not explained by nesting success rates (Table 2). For all five species, most nest initiations ended by about 21 June (Fig. 1).

GIF--proportion of nest initiations
Fig. 1.   Cumulative proportion of nest initiations completed by Julian date among Mallards, Blue-winged Teal, Gadwalls, Northern Pintails, and Northern Shovelers during spring and early summer, 1993 to 1995, in the Prairie Pothole Region of North Dakota and north-central South Dakota.

Table 1.   Mean range of Julian dates when 50, 75, 90, 95, and 99% of nests initiated by Northern Shovelers, Northern Pintails, Blue-winged Teal, Mallards, and Gadwalls were complete during 1993 to 1995 in North Dakota and north-central South Dakota.
Species n % Nest initiations completed by Julian datea
50 75 90 95 99
Northern Shoveler 928 130-138A 141-149A 154-159A 159-164A 169-173A
Northern Pintail 902 132-136A,B,C 146-149A,B 155-160A 161-167A 167-176A
Blue-wing Teal 2,783 135-142B,C 149-152B,C 162-164B 167-170B 173-178B
Mallard 1,167 138-139B 153-157C 163-167B 168-172B 175-183B
Gadwall 2,314 147-154D 157-164D 167-172C 172-177C 179-181C
a Within columns, entries with the same superscript are not significantly different (P > 0.05).

Table 2.   Mayfield nesting success (95% confidence limits in parentheses) for Northern Shovelers, Northern Pintails, Blue-winged Teal, Mallards, and Gadwalls during 1993 to 1995 in North Dakota and north-central South Dakota.
Speciesa 1993 1994 1995
Northern Shoveler 0.34 (0.26-0.43) 0.53 (0.48-0.59) 0.39 (0.34-0.44)
Northern Pintail 0.33 (0.24-0.45) 0.41 (0.35-0.48) 0.29 (0.25-0.34)
Blue-winged Teal 0.32 (0.28-0.37) 0.42 (0.38-0.45) 0.36 (0.33-0.39)
Mallard 0.26 (0.20-0.33) 0.37 (0.33-0.42) 0.32 (0.28-0.35)
Gadwall 0.39 (0.34-0.44) 0.45 (0.41-0.49) 0.32 (0.29-0.35)
a Sample sizes of nests from 1993 to 1995, respectively, are: Northern Shoveler = 134, 367, 410; Northern Pintail = 96, 293, 500; Blue-winged Teal = 456, 884, 1,306; Mallard = 198, 537, 859; Gadwall = 352, 785, 1,098.

Interspecific differences in breeding frequency and distribution during summer. — Of broods seen on transects and plots during September and estimated to have hatched from nests initiated after 10 July, 81 of 82 (99%) were Mallards, Blue-winged Teal, and Gadwalls (Table 3, Fig. 2). Mallards, Blue-winged Teal, and Gadwalls continued to nest an estimated 58, 56, and 47 days, respectively, beyond the summer solstice (Fig. 2). The last nest initiations for Blue-winged Teal, Mallards, and Gadwalls, based on fall brood surveys, were estimated to be 18, 16, and 7 August, respectively. The latest estimated nest-initiation date for a dabbling duck species, based on an opportunistic sighting, was 3 September for Mallards (based on a class 1 brood sighted on the FBSA during late October 1993). The last Mallard, Blue-winged Teal, and Gadwall nests known to have been initiated in 1993 were near the low end of day lengths that stimulated breeding in spring (Fig. 2). Blue-winged Teal accounted for 70 and 83% of dabbling duck broods observed from nests initiated after 10 July 1993 and 1994, respectively. Mid- and late summer nesting was most frequent during 1993 (Table 3). The number of broods seen on transects from nests initiated after 10 July declined sharply from 1993 to 1994 and 1995 (Table 3), as did sightings of dabbling duck broods across the FBSA.

Table 3.   Species composition (%) of Mallard, Gadwall, Blue-winged Teal, Northern Shoveler, and Northern Pintail broods that hatched from nests estimated to have been initiated during mid- and late summer (after 10 July). Surveys were conducted during September 1993 to 1995 on 18 transects randomly distributed across Barnes and Stutsman counties, eastern North Dakota. The number of broods seen during surveys is in parentheses.
Species 1993 1994 1995
Transects Plotsa Transects Transects
Mallard 3.2 (1) 23.3 (10) 16.7 (1) 0.0 (0)
Gadwall 19.4 (6) 9.3 (4) 0.0 (0) 50.0 (1)
Blue-winged Teal 74.2 (23) 67.4 (29) 83.3 (5) 50.0 (1)
Northern Shoveler 0.0 (0) 0.0 (0) 0.0 (0) 0.0 (0)
Northern Pintail 3.2 (1) 0.0 (0) 0.0 (0) 0.0 (0)
   Total 100.0 (31) 100.0 (43) 100.0 (6) 100.0 (2)
a Data from six plots surveyed one to nine days after the initial transect survey.

GIF--breeding intervals
Fig. 2. Breeding intervals for Mallards, Northern Pintails, Northern Shovelers, Blue-winged Teal, and Gadwalls by day length during spring and summer of 1993 in eastern North Dakota. White circles denote one or more nest initiations based on nest surveys conducted from early May through early July 1993 in North Dakota and north-central South Dakota. Black circles denote dates or one or more nest initiations based on broods sighted on transects and plots surveyed during 20 to 30 September 1993 in Barnes and Stutsman counties, eastern North Dakota. Summer nest-initiation dates were estimated by backdating broods of known age class. Some records denoted by white and black circles are hidden from view because of multiple nest initiations on the same date.

Ninety-eight percent (58 of 59) of flightless young of the five species shot on or after 1 October 1993 to 1995 by duck hunters across the United States were Mallards, Blue-winged Teal, and Gadwalls. Only one flightless juvenile shoveler, and no flightless juvenile pintails, were in the sample of wings. Flightless young Mallards, Blue-winged Teal, and Gadwalls reported by hunters were from 7, 5, and 4 states in the western and central United States (Table 4). The number of shot flightless juveniles that came from nests initiated in mid- or late summer declined from 35 in 1993 to 12 each in 1994 and 1995.

Table 4.   Species composition and geographic distribution of flightless juvenile dabbling ducks shot on or after 1 October by a random sample of hunters during 1993 to 1995 based on the annual duck harvest survey conducted by the U.S. Fish and Wildlife Service.
State Blue-winged Teal Mallard Gadwall Northern Pintail Northern Shoveler Totals
California 1 1
Colorado 1 1
Michigan 1 1
Minnesota 1 2 3
North Dakota 5 15 9 1 30
Nebraska 2 3 5
Nevada 1 1
Oregon 1 1
South Dakota 4 6 3 13
Wisconsin 3 3
   Totals 13 31 14 0 1 59

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