Accurate determination of age is of fundamental importance to populati
on and life history studies of waterfowl and their management. Therefo
re, we developed quantitative methods that separate adult and immature
blue-winged teal (Anas discors), cinnamon teal (A. cyanoptera), and n
orthern shovelers (A. clypeata) during spring and summer. To assess su
itability of discriminant models using 9 remigial measurements, we com
pared model performance (% agreement between predicted age and age ass
igned to birds on the basis of definitive cloacal or rectral feather c
haracteristics) in different flyways (Mississippi and Pacific) and bet
ween years (1990-91 and 1991-92). We also applied age-classification m
odels to wings obtained from U.S. Fish and Wildlife Service harvest su
rveys in the Mississippi and Central-Pacific flyways (wing-bees) for w
hich age had been determined using qualitative characteristics (i.e.,
remigial markings, shape, or wear). Except for male northern shovelers
, models correctly aged < 90% (range 70-86%) of blue-winged ducks. Mod
el performance varied among species and differed between sexes and yea
rs. Proportions of individuals that were correctly aged were greater f
or males (range 63-86%) than females (range 39-69%). Models for northe
rn shovelers performed better in flyway comparisons within year (1991-
92, La. model applied to Calif. birds, and Calif. model applied to La.
birds: 90 and 94% for M, and 89 and 76% for F, respectively) than in
annual comparisons within the Mississippi Flyway (1991-92 model applie
d to 1990-91 data: 79% for M, 50% for Fl. Exclusion of measurements th
at varied by flyway or year did not improve model performance. Quantit
ative methods appear to be of limited value for age separation of fema
le blue-winged ducks. Close agreement between predicted age and age as
signed to wings from the wing-bees suggests that qualitative and quant
itative methods may be equally accurate for age separation of male blu
e-winged ducks. We interpret annual and flyway differences in remigial
measurements and reduced performance of age classification models as
evidence of high variability in size of blue-winged ducks' remiges. Va
riability in remigial size of these and other small-bodied waterfowl m
ay be related to nutrition during molt.