|Tawny Grassbird, Jerrabomberra Wetlands, Canberra; a newcomer moving south.|
No, I am surmising that this is a response to climate change, pushing or encouraging warmer climate birds further south (as is happening in reverse in the Northern Hemisphere).
Less than 20 years ago the Pacific Koel Eudynamys orientalis, a big dimorphic parasitic cuckoo which overwinters in Indonesia and New Guinea and breeds in northern and eastern Australia, was a very rare phenomenon indeed in Canberra, though the odd one would occasionally overshoot and lob up here for a while. Within the space of a few years it became a more and more common occurrence, until now it is a part of our urban soundscape (one is calling outside as I write). People have almost even given up writing to the paper to complain about its 24 hour a day strident serenade! They now breed here annually. There is no plausible explanation for this other than climate change.
|Pacific Koel; male (above) and female (below).|
Another large cuckoo, the Channel-billed Cuckoo Scythrops novaehollandiae, has a very similar distribution and annual movements. It is still rare in the ACT (ie I’ve never seen one here yet! though a couple of weeks ago I heard one fly raucously by outside) but it too is getting commoner each year, and I judge that they will also be breeding here in years to come.
|Channel-billed Cuckoo, Karumba, north Queensland.|
|White-headed Pigeon, Nowra, New South Wales south coast.|
Nor is it even just animals. In a remarkable study begun in 2003 in the Manu Biosphere Reserve in the Peruvian Andes east of Cusco US ecologists Miles Silman and Ken Freeley banded and measured 14,000 trees of 1,000 species in 14 plots covering 2,400 metres of altitude. After repeat measurements they discovered that an astonishing 85% of tree genera were moving upslope in response to warming at a rate of 2.5 to 3.5 metres per year. Perhaps the most pertinent aspect of this however is that the authors estimate that this rate would need to double for the trees to keep pace with the observed warming. (The link above will take you only to an abstract unless you're a subscriber; see here for an overview.)
|Cloud forest, Manu Biosphere Reserve, in the area that Silman and Freeley are monitoring.|
But this isn’t the only observed forced reactions of species; there are numerous data sets concerning changes in phenology characters – that is cyclical, especially annual, events such as breeding and migration. As far back as 2003 a wide-ranging review in the prestigious journal Nature revealed “significant mean advancement of spring events” by 2.3 days per decade. Five years later the Intergovernmental Panel on Climate Change’s 2007 report reported that the arrival of spring had been advanced by up to 5.2 days per decade over the past 30 years. Examples cited ranged from first and last appearance of leaves on Gingkos (G. biloba) in Japan, to butterfly emergence in Britain, to bird migration in Australia.
|Gingko leaves, Canberra.|
|Leafy Bossiaea B. foliosa, Mount Ginini, Namadgi National Park, near Canberra.|
Over the past 30 years I have seen the average peak flowering of this pea shrub advance by nearly two weeks.
There are thousands of such phenological studies available, in full or in abstract, or in third-party reports, out there if you’re interested.
In recent times a third general response has been suggested, and demonstrated. While obviously there are always multiple factors acting on the life and evolution of any given organism, we know that in general body size of a given species is likely to be smaller in populations further from the poles – ie in warmer climes. This is known as Bergmann’s Rule and the basis of it is that a smaller object (be it bird, or ball or human baby) has a proportionately greater surface area than a larger one, and thus loses heat faster. We know this for populations of the same species at different latitudes, but what about the same species at the same latitude as climate changes – ie the environment gets steadily warmer? A treasure trove of such data is held in museum specimens throughout the world.
Janet Gardner of the Australian National University, and colleagues, measured 517 museum skins of eight insect-eating birds, collected over 140 years from 1869 to 2001. Six of the species showed a decrease in size since 1950, four of them being statistically significant. The overall impact for those four bird species is that individuals living now at the latitude of Canberra are the size that members of their species were pre-1950 at the latitude of Brisbane (ie 7 degrees of latitude). This I find very striking. Nor is it simply academic - a change in size of even just 4% (as measured in wing lengths by the study) can affect what a bird eats, and thus what it it competing with and must thus further adapt to.
|Birds that are getting smaller as temperatures rise.|
Brown Treecreeper Climacteris picumnus, Canberra (above);
White-browed Babbler Pomatostomus superciliosus Shark Bay, Western Australia (below).
|Twenty-eight Parrot, Cervantes, Western Australia.|
Longer wings to stay cool?
|Eurasian Scops Owl, pale-reddish and dark-reddish forms.|
Illustration taken from Handbook of the Birds of the World, which refers to them as
grey-brown and rufous-brown morphs.
(today I posted a day early, as I'll be away tomorrow)
(And remember that you can get a reminder when the next post appears by putting your email address in the Follow by Email box in the top right of this screen.)