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Determinants of Breeding Distributions of Ducks

Results

Breeding Distributions of the Species

Mallard.—Mallards 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.

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			5^b	20	0^b	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)
	60^c	68			31	48			Lokemoen et al (unpubl. manuscript)^d
	26^e	119							Lokemoen et al (unpubl. manuscript)^d
Gadwall	37	16			12	8	0^b	9	Sowls (1955)
	29	52							Gates (1962)
	66^c								Lokemoen et al (unpubl. manuscript)^d
	40^e								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			0^b	30	0^b	19	Sowls (1955)
	0	16			0^b	200			McHenry (1971)
	5	143			1+	226			Lokemoen et al (unpubl. manuscript)^d
Northern Shoveler	42	19			8^b	12	0^b	12	Sowls (1955)
Northern Shoveler	15	20	11	19	3	116	1	134	Poston (1969)
Northern Pintail	39	44			13^b	115	2^b	132	Sowls (1955)
Redhead	70	23			15	92			Johnson (1978
Redhead	>70	74							Alliston (1979)
Canvasback	75	12			24	50			Bellrose (1980)
Canvasback	76	75	10	52	27	101	1	206	Anderson (1985)
Lesser scaup	20	330	3	34	12	626	0	557	Trauger (1971)
Lesser scaup	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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