Cj. Veltman et al., FORAGING ECOLOGY OF BLUE DUCKS HYMENOLAIMUS-MALACORHYNCHOS ON A NEW-ZEALAND RIVER - IMPLICATIONS FOR CONSERVATION, Biological Conservation, 74(3), 1995, pp. 187-194
We investigated whether blue ducks Hymenolaimus malacorhynchos prefere
ntially capture prey that have themselves become rare or that need to
be present for successful re-establishment. Working at the Manganuiate
ao River in New Zealand, we measured the densities and relative abunda
nces of benthic invertebrates, numbers of prey fragments in faeces of
adult ducks, and foraging behaviour of adult ducks. Invertebrate densi
ties on stones ranged from 3741 m(-2) to 14,417 m(-2). Stone and bould
er communities were dominated by cased cacldisfly larvae or Chironomid
ae larvae in most months. Patterns of apparent selectivity varied but
Trichoptera larvae in the family Hydrobiosidae and in the genus Aoteap
syche (Hydropsychidae) ranked highly, and cased caddis larvae consiste
ntly ranked low, in the diet. Discriminant function analysis indicated
that apparent prey preferences were partly related to whether foragin
g blue ducks were gleaning from the tops or undersides of rocks in the
river. Canonical correlation analysis showed that ingestion of stonef
ly and mayfly larvae was associated with diving behaviour, but it was
not possible to predict the ingestion of other prey from foraging tact
ics. No single prey category was so highly valued by the blue ducks we
studied that it might limit population establishment at new sites.