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Determinants of Breeding Distributions of Ducks

Results


Breeding Distributions of the Species

Mallard.óMallards attained highest densities in prairie and parkland of the southern prairie provinces and in the Copper River and Athabasca River deltas (Fig. 4A). Within the prairie and parkland area, densities decreased with distance from strata of highest densities.


gif --Mallard Distribution

Figure 4. (A) Average species density by stratum, 1955-81; (B) correlation between species density and local pond counts, 1955-81; and (C) correlation between species density and total pond counts, 1955-81.

Most mallards winter in the south-central United States. We estimate from information in Bellrose (1980) that about 70% of wintering mallards return in the spring through the southern entry, or portal (the Dakotas), versus about 30% from California and the Pacific Northwest through the western portal. Thus most mallards initially are exposed to wetland conditions in the southern portion of the surveyed area.

Mallard densities varied with local pond counts, the median correlation coefficient being 0.417 (Table 3). Highest correlations were in Alberta prairie and Saskatchewan parkland, but consistently high values were calculated for the southern portion of the prairie provinces, where mallards were very common, and in the Dakotas (except the 2 easternmost strata), where they were not as common (Fig.4b).


Table 3. Medians and interquartile ranges of correlation coefficients between duck densities and local pond densities, by species, 1955-81.

Correlations with Pond Densities
Species Median Interquartile range
Mallard 0.417 0.159
Gadwall 0.228 0.205
American Wigeon 0.143 0.208
Green-winged teal 0.199 0.181
Blue-winged teal 0.390 0.172
Northern Shoveler 0.388 0.200
Northern Pintail 0.547 0.157
Redhead 0.154 0.220
Canvasback 0.192 0.191
Scaup 0.145 0.182


Mallard densities covaried positively with total ponds in much of their primary range (Fig. 4C). Correlations tended to be negative in many strata in Alaska and the Northwest Territories, as well as in central Manitoba and east-central Saskatchewan, suggesting that those areas are destinations of mallards displaced by drought in the southern prairie-parkland breeding range.

Female mallards, especially those that were successful in hatching a clutch the previous year, home at fairly high rates (Table 4). Males home at much lower rates presumably because pairing occurs during winter or spring migration, and the female leads the male to the breeding ground (McKinney 1965).


Table 4. Reported return rates for 10 species of ducks, by age and sex,a 1955-81.

Adult Yearling
Female Male Female Male
Species % n % n % n % n Study
Mallad 13+ 15     5b 20 0b 13 Sowls (1955)
42 24             Coulter and Miller (1968)
46 113     5+ 140     Doty and Lee (1974)
58 19     14 14     Bishop et al. (1978)
60c 68     31 48     Lokemoen et al (unpubl. manuscript)d
26e 119             Lokemoen et al (unpubl. manuscript)d
Gadwall 37 16     12 8 0b 9 Sowls (1955)
29 52             Gates (1962)
66c               Lokemoen et al (unpubl. manuscript)d
40e               Lokemoen et al (unpubl. manuscript)d
41 54 9 236 7 28 2 42 Blohm (1978, 1979)
American Wigeon 38 21 9 11 33 3 0 6 R. A. Wishart (pers. commun.)
Green-winged teal No information No information  
Blue-winged teal 14 58     0b 30 0b 19 Sowls (1955)
0 16     0b 200     McHenry (1971)
5 143     1+ 226     Lokemoen et al (unpubl. manuscript)d
Northern Shoveler 42 19     8b 12 0b 12 Sowls (1955)
15 20 11 19 3 116 1 134 Poston (1969)
Northern Pintail 39 44     13b 115 2b 132 Sowls (1955)
Redhead 70 23     15 92     Johnson (1978
>70 74             Alliston (1979)
Canvasback 75 12     24 50     Bellrose (1980)
76 75 10 52 27 101 1 206 Anderson (1985)
Lesser scaup 20 330 3 34 12 626 0 557 Trauger (1971)
66 58 9 351 49 76 4 91 A. D. Afton (pers. commun.)

aReported rates are minimal estimates of homing rates, as they do not account for mortality between seasons or for birds that may have homed but were not seen.
bCaptive-reared
cSuccessfully nested previous year.
dJ. T. Lokemoen, H. F. Duebbert, and D. E. Sharp, Reproductive strategies of prairie mallards, gadwalls, and blue-winged teal, unpubl. manuscript, U.S. Fish and wildl. Serv., Jamestown, ND.
eDid not successfully nest previous year.


We conclude that mallards tend to return to breeding areas in the northern states and southern prairie provinces. When wetland conditions in these strata are not favorable, more mallards than usual show up in northern and northeastern strata. If successfully breeding female mallards home at a high rate, dispersing females likely are mostly yearling birds or unsuccessful breeders. Because correlations with ponds are higher in the primary range of the mallard than in the southern portion we suggest that northward-migrating mallards do not fill the habitat as they encounter it from the south, but instead fill the core area first.
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