i will agree with the lower end of your estimate, jack (appx 15%
immature birds present). i did notice something that might be of
interest regarding the flocking of the trumpeter swans; the small
groups of birds contained proportionately more immature birds
than did the large flocks--some of these small groups consisted of
one or two adult birds and three or four immature birds (their
offspring, perhaps?). i had originally begun counting adult and
immature plumaged birds but, once i caught sight of the larger
flocks of swans, i stopped doing this. i do think that a closer
look at these birds would be in order, however, since i was unaware
of the low numbers of immature birds. can you tell me if this is
typical? if so, for how long has this decreased number of immature
birds been noted?

deborah wisti-peterson
department of zoology
university of washington
seattle, washington USA