Birds in Their Habitats
Page 18
Preening
I have a vivid memory of a beautiful Yellow-billed Spoonbill just in front of one of the hides preening, running each wing feather in turn through its broad seemingly unsuited bill, making sure that each was in perfect working order (see Photo 24). Feathers are fundamental to a bird. Keeping them in perfect condition, with all the barbules tightly locked together to ensure that a warm layer of air is kept close to the skin and that the flight and tail feathers are working at maximum efficiency to ensure rapid lift and change of direction when required, can make the difference between life and death. (For details of feather structure and types, see pages 187–9.)
The spoonbill was meticulously ‘rezipping’ the hooks and loops along each barbule of each barb along each feather shaft so that each feather remains pristine. Many species – especially waterbirds, though not parrots or pigeons – use an oily secretion from a gland on the back to spread on the feathers. This cleans, assists with waterproofing, acts as protection against fungi and bacteria and maintains flexibility (which sounds like a commercial!). Many birds have independently evolved powder down: special feathers that grow constantly and never moult, whose tips crumble into a powder-like talc, which is used for cleaning and conditioning. It all sounds a bit pedestrian – and indeed a bird must spend a considerable time at it every day, often in the middle hours when feeding is slow – but I was mesmerised by the care and delicacy with which the spoonbill was performing its maintenance.
Further out on a mud flat, each of a group of Australian Pelicans was performing the same essential self-service. On the way back to the car later, I saw a Yellow-faced Honeyeater likewise assiduously engaged in the foliage.
Every day, in every part of the world where birds live, billions of birds are undertaking the same exhaustively repetitive, but utterly essential, activity.
Other memories of wetlands and rivers
Like bubbles in a churning stream, materialising on a dancing surface, catching the eye briefly before vanishing again into water and air, some briefly surfacing wetland memories:
• The Okavango Delta in Botswana is a remarkable place, and I was fortunate to visit it on a budget-price tour (of necessity, as much as preference), so had the privilege of entering it in a traditional mokoro (plural mekoro): a 3-m long dugout canoe with only 10 cm of freeboard. It is propelled by a poler, armed with a 3-m pole, forked at the end to prevent it sticking in the mud. We were enjoined to trust the poler and not to try to counterbalance when he leans the mokoro – that requires a lot of faith and self-discipline! Sometimes we travelled through alleys cut through the papyrus; sometimes we seemed to cut across country in very shallow water, at others in deep lagoons with the hippos and crocodiles … Birds leapt up whenever we emerged from an alley or turned a corner. And the constant soundtrack comprised the atmospheric wailing yelps of the African Fish Eagles. It was a powerful experience and seemed to mark the beginning of the next stage of my life – an excellent stage as it has turned out, and one that continues 14 years later.
• In Jerrabomberra again, gazing out of the hide early one morning across the mist rising from the waters of Kellys Swamp to the imposing flag pole on Parliament House across the lake. Right in front of me, a long-billed cream and brown streaked wader is darting its bill into the mud at high speed: Latham’s Snipe has flown from its breeding grounds in northern Japan to spend the southern winter in such wetlands. To have the bird in the same field of view as the National Parliament, which has ratified international treaties to protect it, seems very wonderful.
• I always seek out sewage ponds when I travel (and I am often surprised when the town tourist information office professes startled ignorance on the topic). I’ve seen some excellent birds at such places, but none can compare in my memory with Strandfontein in Cape Town, with Table Mountain rearing hugely behind, and the ponds stained pink with hundreds of flamingos. I loved it too that the sewage works at Paarl, northeast of Cape Town, has been delightfully renamed the Paarl Bird Sanctuary and comes with welcome signs, an information shelter, hides and picnic tables!
References
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Alström P, Hooper DM, Liu Y, Olsson U, Mohan D, Gelang M, et al. (2014) Discovery of a relict lineage and monotypic Family of passerine birds. Biology Letters 10(3), 20131067. doi:10.1098/rsbl.2013.1067
Andrewartha HG, Birch LC (1986) The Ecological Web: More on the Distribution and Abundance of Animals. University of Chicago Press, Chicago IL, USA.
Beike M (2012) The history of Cormorant fishing in Europe. Vogelwelt 133, 1–21,
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Carboneras C (2017) Ducks, Geese, Swans (Anatidae). In Handbook of the Birds of the World Alive. (Eds J del Hoyo, A Elliott, J Sargatal, DA Christie, E de Juana). Lynx Edicions, Barcelona, Spain,
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6
Suburbia
Canberra: crafty cockies
Driving down a leafy inner Canberra street through a belt of parkland, I couldn’t help but notice that most of the heavy transparent plastic streetlight covers were dangling below the exposed bul
bs, holding on only by strips of rubber. It could have been interpreted as pretty shoddy construction, were it not for the presence a moment later of the culprits, cheerfully swinging from the damage or gnawing on the rubber seals until they gave way. Sulphur-crested Cockatoos are very handsome indeed: big porcelain-white cockies with a long yellow erectile crest, which have become very well-adapted urban birds in all Australian capital cities except Perth (they were introduced to the south-west in the 1930s but don’t come much into the suburbs). Their beak grows constantly and needs to be kept in trim by gnawing – it may be that urban birds in particular, with a supply of soft fruits and backyard feeders stocked with other soft food, need to spend time in gnawing at random objects including wooden eaves, clothes pegs on lines and, of course, streetlights. They carry seed away in a crop – a thin extendable side-wall to the oesophagus – to digest in safety and at leisure, so have plenty of spare time on their claws. Moreover, they are highly intelligent birds and quite capable of investigating such objects just in case something edible is to be found inside. In recent times, urban Sulphur-crests in Sydney have learnt to open the heavy lids of big plastic wheelie bins to scavenge inside (ABC 2017).
Learning to live in town
This is just one of numerous examples of birds adapting to life in cities, the world’s newest and fastest-growing habitat. A lot of work has gone into studying differences in calls of urban birds from those of their rural ancestors. Forced to compete against a loud background, urbandwelling members of species such as Eurasian Blackbirds and Nightingales in Europe (Reinberger 2013) and Silvereyes in Australia (Potvin et al. 2011) sing more loudly than their country cousins. The Nightingales, however, toned it down at weekends when there was less traffic to compete with. Some species, including Great Tits and Eurasian Blackbirds, sing at higher pitches than they would out of town (Reinberger 2013). Some suggest that this is simply due to the stress of constantly yelling (try it yourself for a while), but a Dutch study (Halfwerk and Slabbekoorn 2009) showed that Great Tits switched to either higher or lower frequencies depending on what background noise they were exposed to – using higher to escape low frequency noise and vice versa. Artificial light is another factor that is entirely novel to birds moving into cities – or even just passing through them. Huge numbers of migratory birds in particular die annually by flying confusedly into lit buildings. One US Government study suggested an annual national figure of between 100 million and a billion such deaths (Kaufman 2011), but impacts can be much more subtle than that. The Max Planck Institute for Ornithology in Seewiesen in Germany is responsible for many such studies, including some of those already cited. In one of these, it was shown that some species – notably Eurasian Blackbirds, European Robins and Great Tits – begin to sing significantly earlier when artificial lights are present. Furthermore, another study demonstrated that, within European cities, male Eurasian Blue Tits living near lights were more successful suitors than those living further away. This may well simply be due to them starting to call earlier than their neighbours, but less easily explained is the fact that females of some species begin to lay eggs some days earlier if they live in the vicinity of a street light (Reinberger 2013). At the other end of the day, House Sparrows in New York and Bangkok forage later into the night, taking advantage of building lights, which attract insects (Donovan 2015). Around the world there must be millions of urban bird feeders dispensing tonnes of food a month to help birds through the tough times – or just to encourage their presence for the owner’s pleasure. One might think that, as long as their owners stick to natural foods, this can only be a good thing, but not necessarily as it transpires. Suburban Florida Scrub Jays are getting prosperous on nuts and other vegetable-based goodies offered to them, to the point where their bodies tell them that because they’re in such good condition they might as well start breeding. Accordingly, suburban jays have begun breeding weeks early, and laying more eggs. Sadly, their chicks need insect larvae as food, not nuts, and if they hatch before spring has properly begun – and they are doing so – they can starve (Anon 2006).
This perhaps leads us to the question as to which birds thrive in cities (it is clear that not all will – birds specialising in rainforests or open habitats, for instance, are unlikely to find their needs there). There are some interesting answers, and some debates. One widely cited earlier proposal (based on data) was that birds with larger brains did well – perhaps unsurprisingly, given the adaptations required (e.g. Maklakov et al. 2011). Other studies have firmly rejected this (e.g. Evans et al. 2011; Dale et al. 2015). The Evans study, across Britain, showed some evidence that eaters of plant parts (including seeds) and birds nesting above the ground were favoured, but a tendency towards being a habitat ‘generalist’ was a more important factor in urban success, again perhaps unsurprisingly. However, the Dale study, in Oslo, reminds us that sometimes the ‘bleeding obvious’ is where we should be looking: although preferred nest site and habitat preferences were important, the key issue in determining which birds were present in town was which ones were present in the surrounding countryside! Clearly there is a gradient from the greenless concrete canyons of the city centres through more or less leafy suburbs with gardens and parks, to the fringes where bushland is still present. In Australia, I think it is fair to say too that aggressiveness is a factor. Notably stroppy native birds such as Australian Magpies, Pied Currawongs, Sulphur-crested Cockatoos, Magpie-larks, Willie Wagtails and crows and ravens simply hold their ground against threats. Most of these – except for the fearlessly cranky little Willie Wagtail and medium-sized Magpie-lark – are large birds. Others, including natives such as Noisy Miners (a colonial honeyeater) and Rainbow Lorikeets, and exotics including Common Mynas and Spotted Doves, will actively attack and displace perceived competitors for feeding sources or breeding habitats. But, it is amazing what can turn up in suburbia, as any bird-aware suburbanite can attest. My previous address, where I spent a quarter of a century, was within a kilometre of the Canberra city centre – but significantly also within a short distance of the Australian National Botanic Gardens and the forested Black Mountain Nature Reserve, and just across the road from the Australian National University, which back then was full of green space (but in recent years has increasingly resembled a chronic building site). Over the years, my yard bird count – defined as birds seen in, over or from the yard – was close to 100. As the plantings grew, so did the list of visitors. One memorable winter, Fuscous and White-naped Honeyeaters regularly visited the saucepan of water hanging in front of my study window. (Fuscous are vanishingly rare garden birds here and White-napeds are not only uncommon in backyards, but are essentially migrants that only come to Canberra to breed in spring and summer.) As I watched one day, distracted from the computer screen, I suddenly felt as though I had strayed into an Attenborough documentary: a young Grey Butcherbird hurtled into the bathing flock of White-napeds, drowned one and flew off with it, the outraged flock in pursuit. None of those three species ever reappeared in the yard. In the last decade of my time there, a prolonged drought and catastrophic wildfires, on the edge of the urban area and even well into it, suppressed the numbers of smaller birds in particular, and the Noisy Miners muscled in, apparently displaced by the building works at the university over the road. After that, things were never the same. Nonetheless, there were still some remarkable moments. So much of birding seems to be chance, happening to be in the right place at the right time – though another way of putting that is that the more hours you put in, the luckier you’re likely to be! One autumn morning I left my desk, slightly reluctantly, to investigate an avian ruckus outside – and saw my first Canberra Eastern Barn Owl blinking confusedly in a tree outside the back door, just before it panicked and was seen off the premises by the mob. Although Barn Owls are common enough across much of Australia, for some reason they rarely turn up in the ACT; there was a brief influx 4 years later, but that’s all I’ve got to show for 37 years here. Even more astonishingly, 6 months
later a Painted Buttonquail, a shy woodland specialist, turned up and spent a week in the yard – fortunately I have a photo to prove that one! And on a summer evening I sat and watched enthralled until darkness hid from me the sky that was full of Pacific (or Fork-tailed) Swifts, from horizon to horizon. Just before flitting to another topic, however, I should mention an intriguing recent paper (Ives et al. 2016) that suggests that perhaps we shouldn’t be too surprised when rarities pop up in our backyards. In a continental-scale study, every Australian town of more than 10 000 people (99 in total) was compared with distribution maps of every listed threatened Australian plant and animal species – 1643 of them. Every single town has, or is likely to have, at least one threatened animal species. Moreover, the study twinned each town with a ‘dummy’ town: an area of the same size randomly selected from the same bioregion. The real towns held considerably more threatened species than the dummy towns (i.e. equivalent rural areas). Without access to the appendices, I can’t separate the birds out of the rest, but it provides nourishing food for thought.