Nature in a Warming World

Last week there was great excitement in our part of the world when a pair of Tawny Grassbirds Megalurus timoriensis turned up at Jerrabomberra Wetlands, our prime suburban wetland in a city which is now very well-provided with such habitats.

Tawny Grassbird, Jerrabomberra Wetlands, Canberra; a newcomer moving south.

This is a notable southern and inland extension of their range from that in the field guides, which is normally regarded as coming to just south of Sydney, some 200km from here and on the coast. Individuals of any species can pop up out of range, especially following unusual weather conditions, but I’m not sure that this is the case here. In the last couple of years (but never before that) there have been at least three reports from Melbourne, on the south coast of Victoria some 600km further south again from here; I would expect that this species, if it were expanding its range, would be more likely to follow the coast rather than move inland. Moreover it is unlikely that they only selected Melbourne and Canberra over all the possible non-urban sites in areas between – it is simply that these are places with lots of bird watchers and I am sure that the bird could, and will, be found in many other places where they used not to be. The Tawny Grassbird is a skulker in dense undergrowth, and I expect (with no expertise) that outside of breeding season it is fairly quiet.

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 Pigeons Columba leucomela have steadily extended their range south from the mid-south coast of New South Wales well into Victoria in the past decade or so, though there is no doubt that part of their enablement has been the spread of exotic food trees like Camphor Laurel Cinnamomum camphora and Privet Ligustrum spp. However, the Camphor Laurel in particular is probably also being assisted to move south by the warming – nature is infinitely subtle.

White-headed Pigeon, Nowra, New South Wales south coast.

As we well know however birds are not the only organisms known to be moving in response to a warming world. A wide-ranging CSIRO study in 2010, utilising a broad array of published and unpublished data, showed that at least 45 species of south-east Australian marine fish have exhibited “major distributional shifts” which were almost certainly climate-related. Warmer water fish from both further north and west have moved into formerly cooler Tasmanian waters, inevitably displacing local species. 

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.

Studies of 175 plant species in six French mountain ranges similarly showed that 118 of them – nearly 70% – had moved at least 18.5 metres (ie 60 feet) up the slope per decade over the twentieth century.

And here of course is the rub; once the Tasmanian cool water fish reach the southern limits of that island (these are coastal waters fish, they can’t just swim out to sea), and the Manu trees reach the treeless puna, the high cold treeless mountain steppes, there is nowhere further to go. It is the same dilemma facing Polar Bears in the Arctic and Mountain Pygmy-Possums on the top of the south-east Australian Alps.

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.

A wide-ranging Australian review, published in 2013, of 89 studies of 347 plant and animal species showed even stronger responses for plants here than in the Northern Hemisphere; the mean rate of advance across all plant responses (leaf set, fruiting, flowering etc) was 11.3 days per decade! Spring migration departure of birds moved forward by 2.2 days per decade (slower than for the Northern Hemisphere, where it was 3.7 days per decade). I mentioned in a recent post how peak flowering of a dominant sub-alpine shrub in the Brindabella Ranges above Canberra has shifted over the 30 years I’ve been taking people up there from about a week into December to late November.

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.

One of the problems with this is that, naturally enough, each species has a slightly different response to the changes, so that finely-tuned systems are no longer functioning as they evolved to do. Bird chicks are hatching before their key caterpillar food supply does, migratory birds including hummingbirds are arriving before or after the flowers they pollinate are open. In the high alps of south-eastern Australia the already Endangered Mountain Pygmy-Possum Burramys parvus emerges from its hibernation with the snow melt – which is getting earlier each year. Unfortunately the great Bogong Moth migration to the high cool granite crevices of the alps is not getting earlier, which leaves the hungry emerging possums without a key food source.

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).

Nature, as I have observed before, is never as straightforward as our little brains might like. More recently apparently conflicting results from those of Gardner’s team were obtained from south-west Western Australia for wing-lengths of Ringneck Parrots Barnardius zonarius (‘Twenty-eights’, for their call, as the sub-species is known over there), which had increased by 4-5mm over the past 45 years. Tellingly, birds from further north in the state, and from the Western Australian eastern deserts, where temperatures haven’t risen as much, show no such increase. The change is as significant as those of Gardner’s were, but in the opposite direction. There is no reason to suppose however that all species in all situations will respond identically to similar situations, and the author suggests that the parrots might be growing longer wings to assist in heat dispersal, in accord with Allen’s Rule.  

Twenty-eight Parrot, Cervantes, Western Australia.
Longer wings to stay cool?

Only ten years ago such responses to climate change were only guessed at, and there will be more surprises to come. One such, which has no obvious explanation for now, is the case of the Eurasian Scops Owl Otus scops, which comes in two colour forms, dark-reddish and pale-reddish (and intermediates). Italian museum studies showed that the proportion of dark-red forms increased significantly over the last century. Some of that was due to unknown causes (perhaps an increase in Italian forests over that time, where being darker could be advantageous, suggest the authors) but the rest is apparently down to climate change. At this stage the best explanation is that the gene for dark-red is linked to one that confers an advantage in a warmer world, but so far we can only speculate.

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.

I am no more interested in arguing about the reality of climate change than I am in debating whether gravity exists or if the sky is blue. It does occur to me though that it would be interesting to hear from someone who has chosen to believe in a fabulous world-wide conspiracy of thousands of scientists, to explain how thousands of species of plants and animals were also persuaded to participate in the deception.

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