The question has been asked, so I'll give information from
Canberra where both species occur (plus several other robin species). This is
based on occurrences with the suburbs, which may be a little different
from in the bush. Here is the text from my: "Canberra Birds: A Report on the first 21 years of the
Garden Bird Survey". I have deleted all the special
fonts as needed to get through to b-a.
Red-capped Robin Petroica
This species is a rare visitor with insufficient records to suggest a trend.
As it arrives from regions to the north and west of Canberra, it is not
surprising that GBS records are only from northern suburb sites.
Rank: 177, A
= 0.00010, F = 0.34%, W = 0.2, R = 0.010%, G = 1.00.
Rose Robin Petroica rosea
This is a less conspicuous bird than the three preceding species, although it
is probably more likely to be found skulking in any suburban garden that has
dense vegetation, than are the other robins. It is primarily a forest bird. Its
mannerisms and habits are fantail-like, rather than like the other robins.
Although it is also an altitudinal migrant, the pattern is not as simple as the
typical pattern, as there is a twin winter peak. There are almost none observed
from October till March, indeed in some years none for several months. The peak
months are in April and August with, in most years, an evident dip within the
cooler months' peak. The Golden Whistler and Grey Currawong have similar
patterns. This suggests that they are passing through either the Canberra region
or the suburban habitat on their way to and then from somewhere else. There has
been a dramatic rise in the abundance of the species. This has occurred in a
most peculiar way. The abundance was quite stable for the first eight years then
suddenly doubled to form a new fairly stable average, it then increased
significantly again during the last four years. There is no survey bias that can
account for this, as it is recorded at many sites. The difference is based on
more than just many more records but more importantly that individual birds or
pairs are staying at the sites much longer than they did in the early years. The
number of weeks of the year that they were recorded (W) jumped from an average
of 11 weeks per year for the first 8 years to 20.9 for the last 13 years. It is
hard to suggest why its behaviour has changed. Many records contain repeat
observations of similar numbers for a few weeks.
Graphs on page: 100, Rank:
72, A = 0.01313, F = 13.29%, W = 17.1, R = 1.210%, G = 1.08.