Birds in Their Habitats

by Ian Fraser

  The pardalotes form their own endemic Family of just four species, in one genus. They are very similar in form: all minute with stubby bills and very short tails. The first edition of my favourite field guide described them as like ‘flying beetles’ (Pizzey and Doyle 1980). (Sadly, later editions had no room for some of those elegant perceptions, which were a hallmark of the great Graham Pizzey, who is unfortunately no longer with us.) Spotted and Striated Pardalotes are very familiar to city dwellers along the east, south and south-west coasts, though Striateds are also found across most of the country. (‘Striated Pardalote’ is a delicious oxymoron, incidentally, because ‘pardalote’ is directly from the genus name Pardalotus, meaning ‘leopard-spotted’. Worse still, the ‘Striated’ refers to faint crown-streaks that are only present in southern Australian birds.) The plainer Red-browed Pardalote also has a huge range in the dry inland as far as the north coast, while the even more modestly attired Forty-spotted Pardalote is a Tasmanian endemic. All nest in hollows, either ground-excavated or in tree cavities.

  In the compost heap, the female Spotted Pardalote seemed to be doing most of the initial work, breaking the surface first with her bill and then digging with her feet (not that I could see what she was doing once she got below the surface, of course, just the spurts of soil erupting from the entrance), but both birds took over after that. They would have continued horizontally for anything from 25 cm to a metre, digging a circular hole 4–5 cm in diameter, which eventually expanded into a chamber up to 10 cm across which they line with fibrous eucalypt bark and dry grass. Like other pardalotes, they lay three or four white eggs – no need for camouflage in a burrow – that they incubate for about 3 weeks, after which the chicks take another 3 weeks or so to fledge. This is in contrast to those of other small foliage-gleaners, which build open cup nests, lay fewer eggs and get them into the world more quickly (Woinarski and Bonan 2017). It seems that the burrows allow a more leisurely approach, which implies less stress on the parents.

  Spotted Pardalotes will sometimes use building cavities or even hanging plant pots, but mostly concentrate on excavated burrows, as do Red-broweds. On the other hand, Forty-spotteds usually use tree hollows, and Striated Pardalotes use both fairly equally (though curiously not in Canberra, where they mostly stick to trees).

  Birds in burrows

  A burrow makes great real estate! Even in blazing summer, it remains relatively cool and moist and in winter it stays much cosier than the blizzard above. It can provide pretty fair fire protection too. (And no, I have no vested interests in the burrow marketing industry!) A burrow also greatly limits the predators that can get at you; however, unless you provide extra exits, it can be pretty dodgy when an enemy does come calling. The pardalotes certainly know that, exploding out of the hole with a leap and opening their wings when already airborne. Their reentry takes the form of a headlong dive. Roaming cats will wait in ambush by the burrow and I did my bit to help by putting a wide-meshed cage over the hole, which gave the birds a bit more of an edge.

  When we think of burrowing animals we are most likely to think of mammals, and with very good reason: many mammal species, from at least 30 Families that I can think of, live or breed in burrows. Many reptiles do too, not to mention invertebrates because they are just too numerous to cover meaningfully! But birds don’t spring readily to mind in this context. Why don’t more birds use burrows? For a start, delicate bones and a bill are not generally the best digging equipment. Then there are the wings: a bird’s best escape mechanism is not going to work underground. Moreover, those same wings mean that a bird can much more readily escape the heat, aridity, cold, fire or predator that surface-bound animals use a burrow to avoid, so they have less need of one.

  Despite all these reasons, many birds do at least breed in burrows, though, as far as I know, only the little Burrowing Owl of the Americas lives in one all year round. However, when I counted, I was surprised to find that there as many bird Families containing burrow nesters as there are mammal Families, though I also note that there are ∼50% more Families of birds (roughly 235–240) than there are of mammals (155–160) (see Photo 25).

  I can think of some 30 bird species that nest in burrows in Australia. Some – including some of our rarest tropical parrots and the apparently extinct Paradise Parrot, plus eight kingfisher species – dig into termite mounds, both arboreal and terrestrial. This comes with an added bonus for the eggs and chicks, because the hosts undertake a certain amount of temperature control. The downside is that termite mounds are hard. It is painful to read accounts of kingfishers flying flat out and bill-first into a rock-hard mound to chip away at the hard shell (e.g. Hollands 1999). Fatalities have even been recorded in the attempts (Woodall 2017). Once inside, female Buff-breasted Paradise-kingfishers use their impressive tail to sweep dirt out (Woodall 2017).

  Presumably, the hooked bills of the parrots are more suited to the task. Golden-shouldered Parrot females do most of the work, digging with the bill and scraping dirt away with the feet. They have to get their timing right, however: if they start too early in the wet season, the termites will simply seal the holes again, or even cement the eggs to the floor, presumably as part of nest management (Garnett and Crowley 2017).

  If digging into soil, one can select a more favourable substrate, though, if it is too easy to dig, the hole is also likely to collapse. Rainbow Bee-eaters dig in a flurry of activity, dislodging soil with the bill while balancing on wings and feet, then hurling it out behind with pedalling feet, balanced now on a triangle of bill and wings. Their burrow, which can be 1.5 m deep, progresses at ~8 cm a day. Webbed feet obviously make good shovels, because a pair of Wedge-tailed Shearwaters can apparently knock up a 15 cm diameter, 1.5 m long burrow, plus a 30 cm chamber in the end, in a mere 6 nights work (though I confess that I can’t now actually find where I read that).

  Remarkably, on Rottnest Island off Perth, Western Australia, it has been calculated that each hectare of a Wedge-tailed Shearwater colony comprised more than 5 km of tunnels, involving the displacement of 210 tonnes of soil (Bancroft et al. 2008)! Other burrowing birds are pretty assiduous in their excavations too: one of the most impressive is the Burrowing Parrot (or Patagonian Conure), mostly of Argentina. Their burrows can be 3 m long, zig-zagging into cliff faces and joining other burrows to form a great labyrinth. One colony contained 35 000 active nests along 12 km of cliff face! (Masello and Quillfeldt 2005).

  Some of these birds – the pardalotes, as already mentioned, and some kingfishers, for instance – are only optional burrowers, using tree hollows at other times. Other birds also use other folks’ burrows opportunistically. Australian Pratincoles hide chicks in rabbit burrows, presumably in place of those sadly no longer provided by bilbies or bettongs.

  Dinosaurs in my garden

  I don’t think that any informed opinion doubts that the pardalotes and thornbills fluttering at the foliage outside my window are, for all meaningful purposes, dinosaurs. In 2007, a publication in the prestigious journal Science claimed to have extracted protein sequences from bones of a 68 million year old dinosaur (Tyrannosaurus rex), which are closest to birds among living animals (Asara et al. 2007). There was some disagreement about the reliability of this, but there is a mountain of other evidence, especially from the vast wealth of palaeontological treasures emerging in China, that birds arose among the running predators that gained infamy as the ‘raptors’ of Jurassic Park, and which were in the same dinosaur group as Tyrannosaurus.

  Elsewhere, I have alluded to some of the essentially birdy traits that derived from their dino-ancestors: feathers (originally for insulation); the ability to maintain a constant body temperature (i.e. ‘warm-bloodedness’, or more properly homoeothermy); and the air sacs that enable a far more efficient lung function than our own.

  Eggs themselves cannot be claimed in this category – they pre-dated even reptiles, let alone dinosaurs, when amphibians began to wrap their embryo in a parchment-like sac to enable them to br
eak the shackles binding them to water. However, the quite different calcium-based shells that enclose bird eggs were certainly inherited from dinosaurs, as is the habit of brooding those eggs in a nest (initially on the ground) as opposed to burying them and leaving the hatchlings to make their way in the world. There are a surprising number of fossilised brooded clutches on which to base this claim (e.g. Norell et al. 1994, 1995). The realisation that eggs in exposed nests (i.e. brooded ones) are significantly less porous than those that are buried has greatly assisted in analysis of fossilised clutches (Tanaka et al. 2015). There is even evidence that Sensitive New Age Dinosaur dads took their turn at brooding (e.g. Birchard et al. 2013).

  Chinese fossils have been found of dinosaurs that died in their sleep, with their heads tucked under their arms in the same posture as modern sleeping birds (Xu and Norell 2004).

  Don’t you love the concept that, even as we speak, a great great great (etc.) grand-niece of Tyrannosaurus rex is gleaning insects from a leaf near you?

  Other memories of suburbia

  Like moulted feathers drifting erratically down from the sky (will it land in my yard or not?), some unconnected thoughts of urban birds:

  • In Guayaquil, the largest city in Ecuador, a crowded sprawling industrial town on the mighty Guayas River, a bright green and red cluster of Red-Masked Parakeets is noisily squabbling over a pipe extending from a building wall in the city centre, probably hoping to secure a nesting hollow. Sadly, this lovely boisterous bird is declining in its woodland habitats, partly because of loss of that habitat, but even more due to the voracious demands of the pet trade.

  • Buenos Aires is a pulsing city of 3 million people. In the brief couple of days we were there, we didn’t see a single stand-alone house, because everyone seems to live in high-rise apartment blocks. This is dense living! But, despite the constant swirl of people, we kept finding little parks, swamped in the roar of traffic, but supporting birds. A natural inhabitant of disturbed areas, the rusty-coloured Rufous Hornero has happily taken to the parks, to the extent that it has been declared Argentina’s national bird! Attractive Rufous-bellied Thrushes join them on the grass, while above them speckle-necked pinkish Picazuro Pigeons have only recently discovered the benefits of urban life. In one especially seedy and busy little park, we even stumbled across a single Guira Cuckoo: they are known to adapt to urban living, but are renowned as highly sociable birds. A little mystery.

  • Douala is another city in the 3 million club: the biggest city in Cameroon, and a serious shock to the system for someone unused to less-developed countries. My trip diary described it as ‘vast, throbbing, noisy, frantic, hustling chaos’, and the traffic as ‘surreal lunacy’. Nonetheless, before we fled to the countryside we stopped in at a little area of gardens behind a razor-wired industrial complex by the huge Wouri River where a pair of African Grey Parrots flew overhead, flashing their red tails. Welcome to West Africa!

  • Lima, the capital of Peru, is a huge throbbing intimidating mass of 10 million people, many of them poor rural residents who come to try to find work. One more placid area is that of Miraflores by the Pacific, which, because of the cold Humboldt Current onshore (and doubtless also pollution), is always shrouded in grey. Here, in a small park, I came across an Australian bottlebrush (Melaleuca sp., formerly Callistemon), flaunting big red flower spikes. And availing itself of the nectar bounty was an Amazilia Hummingbird: a dryland green and rufous beauty with bright red bill, which has adapted to city living.

  • Kampala, the Ugandan capital, is another rapidly growing crowded city, though its situation on the shores of Lake Victoria is ameliorating. The rooflines are strangely distorted by the huge louche shapes of menacing Marabou Storks resting between visits to the garbage dumps and abattoirs.

  • An agitation of birds outside my study led me downstairs and cautiously into the backyard, where a little Collared Sparrowhawk glowered fiercely at me from the shadows of the tea-tree, daring me to take away the recently deceased House Sparrow clutched in her claws. Eventually she flew off with it to dine somewhere quieter (see Photo 26).

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