Recruitment in the process by which young birds are added to tile breeding
population. The two most commonly used methods to estimate recruitment in d
ucks are pair/brood counts, and fall age ratios based on wings returned by
hunters. Direct counts on the wintering al-ea to determine the proportion o
f young males to adult males (age ratios), can be used for species with del
ayed plumage maturation. This is useful for species that are difficult to s
tudy on tile breeding grounds and are seldom hunted, such as Harlequin Duck
s (Histrionicus histrionicus). Such an approach is only valid if age classe
s are equally sampled. Between 1994 and 1999, the proportion of male Harleq
uin Ducks that were immatures in thr Strait of Georgia, British Columbia, M
as estimated at 0.068. The proportions differed across years. Little differ
ence occurred through the winter months until spring, when there was a sign
ificant increase in proportions in March. If these age ratios are accurate,
then recruitment would not be compensating for annual adult mortality and
the population could have been declining during the period of our study. Ho
wever, if immature males are not distributed evenly among the population, t
hen our assessment may underestimate ol overestimate proportions. Delayed b
reeding means that immature birds experience several additional seasons of
mortality prior to breeding, and thus the actual recruitment I ate into the
breeding population would be lower than tl-lat presented here.