An excellent question, Tom, which prompts me, as Ian
recommends, to have a bit of a speculate.
I have noticed pardalotes and weebills attacking large lerps
and getting hold of big fat psyllids. I have also noticed feeding
wattlebirds flicking away the scales and collecting a spattering of them over
their bills/faces. On the other hand, with parrots and Gang-gangs my
impression is that they clean off and swallow the whole thing - if
they can. I had thought they were targeting the sugary scale, and didn't
care if the insect had vacated it or not.
With the heavy lerp infestation at Belconnen, the lerps
seem to be quite small, and many seem fresh. Probably the psyllid
nymphs are at home. Would that not be a great source of protein,
particularly for the dependant birds, and one that would be very
accessible to the parrot's feeding method? I have noticed that the
regurgitated food dribbled to the young is a thick sticky liquid. Sugar
for energy and protein for growth (are the adults in moult as well?) would be
available in the one hit. (I ran into Henry Nix while mulling over that
this morning, and in a brief conversation he agreed, although he may wish
to reserve his position on whether or not that was out of
politeness.)
I don't know much about the psyllid infestation cycle,
annual or multi-year, but I gather from the web pages that they can be quite
localised. The concentration in Belconnen might be the best for many
miles around. I have suspected for some time that lerps, like
politicians, represent a field where Canberra can more than
hold its own against other regions of Australia. From ordinary
observations, quite a bit of visiting bird activity is aimed at them (lerps
that is, not politicians). The returning Swift Parrots with young were
attacking lerps last Autumn at Hackett, unlike - as I recall - the
adults that were south-bound in Spring. (Debbie will have fuller notes
on that.)
