by Nicholas Munday, Adelaide Urban Birding

Previous articles in this series, What Bird Is That?, have explored common, widespread and conspicuous birds that call Your Adelaide Park Lands home.

However, the subject of this article is altogether more cryptic and uncommon, although very much worthy of attention: the eastern spinebill (Acanthorhynchus tenuirostris).

Eastern spinebills are likely not a bird that many people would immediately recognise. Although, anyone who still uses cash may have seen its likeness before. Since 2016, it has been featured on the $5 note.

It is a species that no doubt deserves more recognition when it comes to birds in the Australian public consciousness.

Eastern spinebills are diminutive yet striking members of the honeyeater family, Meliphagidae, which include better-known birds such as the noisy miner (Manorina melanocephala) and the New Holland honeyeater (Phylidonyris novaehollandiae). 

As their common name suggests, there are two members of the spinebill genus, Acanthorhynchus (the genus name derived from the Greek, literally, for ‘spine’ and ‘beak’ or ‘bill’) - those being the eastern and the western spinebill. 

The representative found in Adelaide is the eastern species. Unsurprisingly, it is found along the east coast, being distributed across the length of the Great Dividing Range, throughout Victoria and much of South Australia from the South-East to the southern Flinders Ranges. It is also found across the Bass Strait throughout Tasmania. 

It prefers well forested habitats - particularly dense Eucalypt woodland - and is more often encountered in the Adelaide Hills than on the plains, although it is seasonally nomadic and usually more plentiful around the Adelaide suburbs during the cooler months of the year.

The arguably even more striking Western species - Acanthorhynchus superciliosus - is found along the south-western corner of Western Australia in mostly heathland environments, up to the edge of the Nullarbor Plain. 

Neither species occupies truly arid habitats. They are thought to have diverged from each other during the last ice age - when increasing aridity drove their ancestors into wetter refuge habitats in the southwest and southeast of the continent, respectively. 

The sparsely vegetated Nullarbor Plain continues to serve as a natural barrier for the two species today.

Eastern spinebills prefer densely vegetated environments. Across the east coast of Australia, they seem to prefer wet Eucalypt forests, although in South Australia they can be found in more open environments.

Spinebills are apparently one of the earliest divergences within the honeyeater family. While honeyeaters, as the name suggests, universally prefer nectar over other food sources, spinebills have evolved to take nectar feeding to extremes. 

The characteristic ‘spine bill’ is suited to little else except probing deeply into flowers for nectar, although they will eat insects to supplement their protein and nutrient intake (nectar alone being loaded with carbohydrates but little of anything else).  

In natural environments, they are the primary pollinators for many tube-flowered Australian plants such as Native Heaths (Epacris species) and Native Fuchsias (Correa species), although they will take nectar from pretty much any suitable flower, native or exotic. 

Within suburban Adelaide, they appear to have adapted to a variety of non-natives, and have a particular fondness for cultivars of Fuschia and Salvia, which offer the perfect combination of abundant nectar and protective cover. 

Eastern spinebills are about the only Australian honeyeater that can hover in flight (at least, for any meaningful period of time) when feeding from flowers, allowing them to exploit a more diverse range of nectar sources that are otherwise inaccessible to birds.

That being said, they are far from experts at it, and can only maintain the feat for short intervals.

In this way, the spinebills have convergently evolved to fill a niche occupied by similar nectar feeding birds of other continents, analogous to the hummingbirds of the Americas (Family: Trochilidae) - which among the birds are the undisputed masters of hovering flight - and the sunbirds (Family: Nectariniidae) found over much of Africa and Asia (and interestingly with a sole representative in Australia in the olive-backed sunbird (Cinnyris jugularis) found in tropical Queensland). 

Eastern spinebills exhibit some degree of sexual dimorphism, although it is only subtle and the sexes are virtually indistinguishable when seen at a distance. 

Males are typically more vibrant than females, with a black capped head and bold contrasting wing and breast markings. In contrast, these markings are a more muted grey-olive in females. 

The difference is almost imperceptible when observing individual birds, as they rarely stay still for more than a few moments as they flit rapidly from flower to flower in their insatiable hunt for nectar.

As mentioned, while the eastern spinebill is an Adelaide Park Lands resident, it is most often encountered during the cooler months of the year, particularly between late autumn and early spring. 

They are more often heard than seen, as they proclaim their territory with a melodious, piping song. 

By far the largest congregations can be found at Park 11 (particularly the Adelaide Botanic Garden, but also Botanic Park and the Adelaide Zoo).

Sporadically, they will also turn up at other parks, looking for suitable flowering plants. So be sure to keep a careful eye out for these delicate, little birds this winter.

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Main photo (top): eastern spinebill amongst purple salvias by Nicholas Munday, Adelaide Urban Birding.

Read more articles in our ‘What Bird is That?’ series here.

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Nicholas Munday is an environment and planning lawyer, with degrees in law and science (evolutionary biology and ecology) from the University of Adelaide. 

He has a strong interest in biodiversity conservation and runs the ‘Adelaide Urban Birding’ Instagram account (@adelaideurbanbirding), dedicated to his photography of native birds in the Adelaide metropolitan area.

In his free time, Nicholas is well-known in the Adelaide choral music and theatre communities, and also enjoys bushwalking, writing, and, of course, photography. 

The opinions expressed in this article are entirely those of the author. This author is not affiliated with the Adelaide Park Lands Association.