On a quick read I'm (quantitatively) skeptical.
I can't see enough in the paper to reject the hypothesis that
the change in arrival/departure dates is caused by changes in the
number/distribution/activity of bird watchers.
Another explanation which looks quite tenable for a couple of the
species/locations is increase in bird population size.
Although the press piece says "most likely as a result of global warming",
the paper presents nothing about causality. A lot of things correlate
with time, e.g various aspects of anthropogenic veg modification.
For example, the population of a number of non-migratory Sydney birds,
e.g. Rainbow Lorikeet, have have undergone major changes over the last
50 years. The change in Rainbow Lorikeets likely correlates with time,
but its not convincing evidence that climate change is a major cause.
Incidentally I don't doubt our climate is changing but in eastern NSW
one the significant chances of the last century is said to be decline
in rainfall. This, for some species at least, might favour later arrival.
Andrew
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