Age Determination of American Black Ducks in Winter and Spring

Abstract

Age-specific studies pertaining to survival and productivity of American black ducks (Anas rubripes) are constrained by the fact that no technique has been developed to reliably determine age as second year or after second year from late winter to late spring. We developed a qualitative age-class scoring technique that can be readily used in the field. When tested on 5 independent observers, known-aged birds (n ¼ 106) were correctly classified with 94-98% accuracy. To reduce subjectivity and provide an objective corroboration of age estimates, we also developed multivariate models from measurements of wing feather variables (weight and length of greater secondary covert 9, and width of tertial covert 5) that determined age with !90% accuracy (n ¼ 255). There was !94% agreement between qualitative and quantitative age assignments of wild birds caught in spring (n ¼ 172). The application of these age determination techniques should be useful in a host of life-history studies conducted on wintering, spring staging, and nesting grounds. (WILDLIFE SOCIETY BULLETIN 34(5):

Body condition of American Black Ducks (Anas rubripes) wintering in Atlantic Canada using carcass composition and a scaled mass index

“…We also could not examine the effect of age on body condition (reliable age data were not available). Ashley et al (2006) developed a method to age black ducks in late winter and early spring which relies on examining the shape and structure of certain feathers. This method can fail if feathers are not dry or are excessively worn during the time of capture, and this method can be misleading as a small proportion of some age-sex cohorts exhibit the same traits as other age-sex cohorts (Ashley et al 2006).…”

“…Ashley et al (2006) developed a method to age black ducks in late winter and early spring which relies on examining the shape and structure of certain feathers. This method can fail if feathers are not dry or are excessively worn during the time of capture, and this method can be misleading as a small proportion of some age-sex cohorts exhibit the same traits as other age-sex cohorts (Ashley et al 2006). In general, juvenile black ducks tend to be smaller and in worse condition than adults (Longcore et al 2000), but Hepp (1986) found no difference in the percentage of weight change through winter in juvenile and adult captive black ducks.…”

“…Black ducks from all locations were sampled in winter of 2013-2014, and SMI of these ducks was compared among the three locations using a one-way ANOVA. (Ashley et al 2006), and thus we chose not to include age as a factor. Significance levels were p < 0.05.…”

Blood Lead Declines in Wintering American Black Ducks in New Jersey Following the Lead Shot Ban

“…From 14-19 January 2017, we captured 80 black ducks at Hanson with a rocket net (Dill and Thornsberry 1950) on the shoreline using cracked corn for bait. We determined the sex of ducks by cloacal exam and age as second-year or after-second-year using wing feather criteria (Ashley et al 2006). We then collected a 0.75-1.0-mL blood sample from the ulnar vein of each bird using a sterile 22-gauge, 2.54-cm heparinized needle attached to a 3-mL sterile syringe.…”

Full Issue

“…We banded all black ducks with U.S. Geological Survey standard aluminum tarsus bands and aged birds by wing plumage characteristics (Carney 1992, Ashley et al 2006. Females were weighed with a 2.5-kg Pesola spring scale (Pesola AG, Baar, Switzerland) and only instrumented if a 23-g, harness-type, VHF transmitter (Model A1820, Advanced Telemetry Systems, Isanti, Minnesota, USA) was ,3% of an individual's body mass (~900 g; Dwyer 1972, Gustafson et al 1997.…”