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Survival of Radiomarked Canvasback Ducklings in Northwestern Minnesota

Tables

Table 1. Fate of canvasback broods radiomarked at hatch at the Agassiz National Wildlife Refuge, 1987-90.
1987 1988 1989 1990 Total
Brood Deployments 5 11 23 13 52
Radiomarked ducklingsa 22 43 96 56 217
Brood Lossesb
Total 2 4 5 7 18
Partial 3 5 17 6 31
None 0 2 1 0 3
aDeployed with radiotransmitters within 1 day of hatch.
bIncludes loss sustained during period of radiocontact with brood

 

Table 2. Contributing causes of death of canvasback ducklings radiomarked at hatch at the Agassiz National Wildlife Refuge, 1987-90a.
Year Sex (n1,n2)b Known Predation Possible Predationc Disease Weather Inanition Unknownd
1987 Female (8,0) 7 7 0 0 0 1
Male (6,3) 4 7 0 0 0 2
1988 Female (13,2) 5 7 1 4 1 4
Male (12,4) 5 9 0 2 1 5
1989 Female (33,11) 16 27 1 11 2 6
Male (20,17) 11 28 0 7 3 1
1990 Female (26,3) 19 22 3 2 1 3
Male (17,4) 13 17 1 1 0 3
All Female (80,16) 47 63 5 17 4 14
Male (55,28) 33 61 1 10 4 11
aRow sums may exceed the total number of mortalities for any year-sex class because some deaths have multiple causes of mortality.
bn1 refers to number of recovered carcasses, n2 refers to number of symptomless transmitter failures.
cIncludes known predation and symptomless failure of transmitter.
dCause of death could not be determined.

Table 3. Number of canvasback ducklings killed by predators at the Agassiz National Wildlife Refuge, 1987-90.
1987 1988 1989 1990 Total
Ducklings from hatch to 4 weeks of age
Mink 11 5 9 15 40
Great Horned Owl (Bubo virginianus)   2 1 3 6
Black-crowned Night-heron (Nyctiocorax nyctiocorax)     1   1
American Coot (Fulica americana)   1     1
Other avian     4 5 9
Snapping Turtle (Chelydra serpentina)       1 1
Fox (Vulpes vulpes)       1 1
Unknown Predator   2 8 7 17
Total Depredations 11 10 23 32 76
Ducklings >=4 weeks of age
Mink   1 1 3 5
Snapping Turtle   1     1
Unknown Predator   1     1
Total Depredations   3 1 3 7

 

Table 4. Estimates of Weibull parameters for canvasback ducklings by sex and year at the Agassiz National Wildlife Refuge, 1987-90.
Year Sex Symptomless transmitter failures treated as deaths Symptomless transmitter failures treated as censored
Intercept Scale Intercept Scale
1987 Female 2.12(0.67)a 1.50(0.53) 2.12(0.67) 1.50(0.53)
Male 2.72(0.49) 1.19(0.41) 3.38(0.87) 1.54(0.67)
1988 Female 2.67(0.38) 1.46(0.32) 2.90(0.46) 1.64(0.39)
Male 2.87(0.33) 1.27(0.28) 3.43(0.54) 1.64(0.44)
1989 Female 2.67(0.21) 1.39(0.17) 3.12(0.31) 1.75(0.26)
Male 3.09(0.21) 1.26(0.17) 4.20(0.48) 1.91(0.37)
1990 Female 1.75(0.28) 1.49(0.20) 1.86(0.29) 1.54(0.22)
Male 2.49(0.35) 1.57(0.27) 2.80(0.44) 1.82(0.36)
aValues in parentheses are standard errors.

 

Table 5. Coefficients for sex effect in Weibull model, by year, for canvasback ducklings at the Agassiz National Wildlife Refuge, 1987-90.
Year Symptomless transmitter failures treated as deaths Symptomless transmitters treated as censored
Coefficient P-Value Coefficient P-Value
1987 0.61 0.46 1.24 0.23
1988 0.21 0.67 0.53 0.44
1989 0.40 0.18 1.00 0.05
1990 0.7 0.07 0.98 0.05

 

Table 6.Mortality and estimated daily survival rates (S1) of Class-II canvasback ducklings at the Agassiz National Wildlife Refuge, 1987-90.
Year Sex N Days of Exposure Symptomless transmitter failures treated as deaths Symptomless transmitter failures treated as censored
Deaths S SE Deaths S SE
1987 Female 15 210.0 6 0.971 0.011 0 1.000 0.000
Male 8 152.0 3 0.980 0.011 0 1.000 0.000
1988 Female 16 430.0 4 0.991 0.005 3 0.993 0.004
Male 20 467.0 1 0.998 0.002 0 1.000 0.000
1989 Female 25 805.0 8 0.990 0.003 1 0.999 0.001
Male 28 719.0 6 0.992 0.003 0 1.000 0.000
1990 Female 17 307.5 9 0.971 0.010 3 0.990 0.006
Male 12 276.0 6 0.987 0.009 0 1.000 0.000
All Female 73 1752.5 27 0.985 0.003 7 0.996 0.002
Male 68 1614.0 16 0.990 0.002 0 1.000 0.000
1Survival rate calculated with the Mayfield (1961) method, with standard errors determined according to Johnson (1979).

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