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Mortality During the Breeding Season

Table 12-4. Some Mortality Rates of Prefledged Swans and Geese in North America and Principal Causes of Mortality

			Mortality rates^a
Species/subspecies	Habitat	Location ^b	1st 2 weeks^c	To fledging^d	Mortality causes^e	Source
Trumpeter Swan	Intermountain marsh/lake Intermountain marsh/lake Intermountain marsh/lake Forest deltas	Mont. Mont. Oreg. Alaska		0.20 0.45^f 0.73^f 0.32 0.05 0.23 (0.18 - 0.29) ^f,g	u u, p w, d u u,h,p	Banko (1960) Page (1974) in Bellrose (1980) Cornely et al. (1985a) Hansen et al. (1973)
Tundra Swan	Tundra	Alaska (2)		0.31(0.24-0.39)^f,g	u, w	Lensink (1973)
White-fronted Goose	Tundra Tundra	Alaska Alaska	0.13^h	0.12^h,i	p u	Mickelson (1975) Ely and Raveling (1984)
Snow Goose	Tundra	N.W.T.(7)	0.15^g,h	0.19^{g ,h}	p	Cooch (1958)
Emperor Goose	Tundra Tundra	Alaska Alaska		0.22^h,i 0.32^h	p p	Mickelson(1975) Eisenhauer and Kirkpatrick (1977)
Canada Goose (subspecies)
Western Giant Lesser/Hutchins Cackling	Intermountain marsh/lake Reservoir Forest bog lakes Forest bog lakes Prairie Savanna Tundra Tundra Tundra	Mont. Mo. Mich. Mich. Iowa Wis. N.W.T. N.W.T.(6) Alaska	0.29^g 0.25^g 0.23 (0.13 - 0.35) ^f	0.17, 0.20^f 0.32(0.20-0.36)^f 0.22, 0.28^f 0.84^f <0.10, 0.27^f 0.39(0.28-0.52)^f 0.10, 0.15^h 0.26(0.14-0.39)^f,g 0.13^h,i	u, p u, p, d,w u, p d w, p u p p p	Geis (1956) Brakhage (1965) Sherwood (1968) Sherwood (1968) Nigus and Dinsmore (1980) Zicus (1981) MacInnes (1962) MacInnes et al. (1974) Mickelson (1975)
Brant	Tundra Tundra	Alaska Alaska	0.10(0.03-0.17)^g,h	0.15^h,i 0.29(0.15-0.42)^g,h	p p	Mickelson (1975) Eisenhauer (1977)
^aUnderlined rates pertain to losses of entire broods only; other rates pertain to losses of total young hatched or changes in average brood sizes. Most values are either from 1 year or are weighted averages presented in respective sources; where data exist for 2 years, both values are provided, but where data for 3 or more years were provided, we calculated unweighted means and present the range of annual variation.
^bNumber in parentheses refers to location shown on Figure 12-1.
^cApproximate first 2 weeks after hatch, but length of period varies by about 1 week.
^dApproximate period to fledging, but length of period varies from about 2 weeks before fledging to 3 weeks after fledging.
^eMortality-cause codes are: d = disease, h = human disturbance, p = predation, u = undetermined, and w = weather. If more than one cause was considered significant, the codes are listed in the order of importance implied. Italicized codes were suggested from conclusions in source, but no quantitative data were presented.
^fRate based on total counts of difference between numbers of young hatched and numbers fledged, so losses of entire broods are accounted for even if unspecified, except for Lensink's (1973) study in which mortality was estimated from comparisons to average clutch sizes and thus included unhatched eggs as well as missing cygnets.
^gCalculation made from data presented in source; unweighted average for studies of Hansen et al. (1971), Lensink (1973), and MacInnes et al. (1974).
^hRate based on counts of average brood sizes and does not account for losses of entire broods.
ⁱFrom Mickelson (1975, Table 3); we were unable to obtain these same values from data presented in that table or in appendices.

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