In the article “Age Determination of American Black Ducks in Winter and Spring,” Ashley et al. (2006) show that age-specific research about American black duck’s (Anas rubripes) productivity and survival is constrained. The authors have associated the limitation with the lack of effective technique to determine the ducks’ age in the second year or after the second year between late winter and spring. Their research aimed to develop methods to discriminate second year (SY) from after the second year (ASY) black ducks through qualitative filed techniques and multivariate models.
For Ashley et al. (2006) to research and develop a valuable criterion for reliably separating the ducks’ age classes, they examined wing feathers from four sources. The first two sources were live ducks caught in bait traps in autumn and southern Ontario harvested birds. The last two sources were wings submitted to the Canadian Wildlife Service Species Composition Survey (SCS) and live ducks caught in bait traps between March and April. As potential age indicators, Ashley et al. (2006) considered every wing feather retained until the prebasic moult for inclusion, determined using a three wild hatch-year (HY) black ducks’ cohort. Further, Ashley et al. (2006) examined the chosen feathers based on primary 5, primary coverts 4-7, greater secondary coverts 5 and 9, and tertiary covert 5 to determine their type and position number.
For qualitative analysis, the researchers used the ACS technique, which was limited to the fewest possible feather characteristics that would be consistently and quickly recognized in the field, resulting in a high correct classification level. Based on a 0-4 tailored score, the evaluated characteristics were PC 4-7, which Ashley et al. (2006) analyzed for the absence or presence of juvenile-like buffy cream color pigmentation. The same characteristics were evaluated on PC 4-7 based on pointed, squared, or rounded shapes, TC 5 based on squared, rounded, broadly pointed, or pointed, and based on feather immaturity. Ashley et al. (2006) used the discriminant function analysis method to examine potential criteria for quantitative age separation in feather characteristics. They achieved this using P 5 maximum vane width (VW), mass length (L), GSC 5 and 9, and TC 5, and the same for PC 4 feathers. These were significant to the study since they helped the researchers to develop the appropriate equations from feather variables, which they then used to classify the ducks either as captive, for group 1,or hunter-harvested, for group 2.
Once the researchers evaluated the primary and tertiary coverts characteristics of 127 known black ducks, they tested 106 birds, which they used as their subset. The qualitative findings showed 94-99 percent accuracy in age determination among the captured birds. While the least experienced observer scored 94, the most accurately classified 97 percent of ASY males and 100 percent of females as ACS 3-4 and ACS 2-4, respectively. Further, the observer classified 100 percent of SY males and females to ACS as 0-2 and 0-1, respectively. The researchers used 11 previously branded ducks of known age in spring and found that nine and two were 100 percent ASY males and females of 3-4 and 2-3, respectively. The success of the qualitative model manifested in assigning 0-2 ACS for SY males and 0-1 for females, 3-4 ACS for ASY for males, and 2-4 for females. The result showed the qualitative model developed to determine the age of the ducks was a very accurate approach for Ashley et al. (2006) to distinguish between the male and female birds and their years, SY and ASY.
The quantitative findings showed feather size similarity in autumn-shot birds and captive birds in spring. By pooling feather variable categories for male and female ducks, eight variables revealed differences between group means where the autumn measurements were minor than the spring measurements. With the decision to use spring captives, Ashley et al. (2006) used the WGSC 9 variable to correctly classify the age of 89 percent of the male ducks and 95 percent of the female ducks. The researchers concluded a high agreement between quantitative and qualitative methods to determine black ducks’ ages in spring. That indicated the possibility of accurately determining black duck ages under field conditions.
Reference
Ashley, E. P., North, N. R., Petrie, S. A., & Bailey, R. C. (2006). Age determination of American black ducks in winter and spring. Wildlife Society Bulletin, 34, 5, 1401-1410.