Northern Prairie Wildlife Research Center
|Table 1. Mean differences in body mass (g) of Canvasback and Redhead ducklings within broods by age class.a|
|Sex||Age class||Number of ducklings||Number of broods||Difference in body mass (g)|
|F vs. M||IIA||98||25||103||51.5||43.4||0-250|
|F vs. M||IIA||61||16||67||46.9||37.5||0-135|
| a Where broods
contained ducklings of >1 age class, the data were summarized for
the dominant age class of that sex.
b Number of all possible comparisons within brood.
c Ducklings in Class IIID could only be aged to Class III.
Assessment of factors affecting mean body mass in Canvasback ducklings was complicated by the lack of data in Class IIC and in 1976. By excluding age class IIC and 1976 in the first ANOVA, we were able to balance the design to assess effects of age class, sex, year, and season. Of the 4 factors, age class (F = 38.39; df = 1, 69; P = 0.001) and sex (F = 14.89; df = 1, 46; P = 0.0004) were significant. All other main effects (year and season) and interactions were not significant. Because season did not seem to account for variation in mass, we conducted a second ANOVA including Class IIC and 1976 and ignoring season. Effects of age class (F = 168.75; df = 2, 161; P = 0.0001), sex (F = 56.75; df = 1, 97; P = 0.0001), and sex-by-age class (F = 3.75; df = 2, 97; P = 0.0271) were significant. Within age classes, mean mass of male and female Canvasback ducklings did not differ in Class IIA but did differ in older age classes (Table 2).
|Table 2. Mean body mass (g) of Canvasback ducklings, expressed as LSMEANS, by age class and sex.|
|Age class||Number of broods||Number of ducklings||Sex||a||SE|
|a Means within age class followed by a common letter are not significantly different (P > 0.05) using Fisher's protected LSD value.|
Analysis of factors affecting variance of body mass within Canvasback broods was inconclusive. Although the overall test of no difference was significant (F = 10.08; df = 34, 25; P = 0.0001), when the main effects (year, season, age class, and sex) were analyzed separately, no effects or interactions were significant (P > 0.35).
Variance within broods was less than that among broods for both Canvasback and Redhead ducklings, except for Class IIC Canvasback females and Class IIA Redhead males (Table 3). Variance was highest among broods for Class IIIA female and IIID male Canvasbacks and IIID female Redheads, but sample sizes were small.
|Table 3. Variance in body mass of Canvasback and Redhead ducklings among and within broods, by age class. Percent contribution to total variance is in parentheses.|
|Sex||Age class||Number of ducklings||Number of broods||Variance|
|Among broods (%)||Within broods (%)|
|F||IIA||54||21||3,670 (75)||1,212 (25)|
|IIB||111||36||6,432 (63)||3,784 (37)|
|IIC||86||28||2,285 (42)||3,166 (58)|
|IIIA||9||5||-90a (0)||3,738 (100)|
|IIID||16||9||6,111 (79)||1,588 (21)|
|M||IIA||55||22||6,137 (82)||1,391 (18)|
|IIB||102||39||6,051 (63)||3,502 (37)|
|IIC||104||32||5,593 (59)||3,845 (41)|
|IIIA||14||8||3,693 (69)||1,655 (31)|
|IIID||22||10||794 (12)||5,953 (88)|
|F||IIA||36||18||3,912 (65)||2,115 (35)|
|IIB||48||24||3,496 (57)||2,590 (43)|
|IIC||30||18||2,668 (59)||1,825 (41)|
|IIID||6||4||-661a (0)||1,906 (100)|
|M||IIA||43||19||3,596 (47)||4,023 (53)|
|IIB||53||21||4,863 (60)||3,231 (40)|
|IIC||19||13||4,733 (71)||1,890 (29)|
|IIID||10||7||3,194 (94)||189 (6)|
|a Variance component not different from 0.|
We found no significant differences in body mass between single- or mixed-species broods for any age class, sex, or species (Tables 4 and 5).