Australia has an enormous variety of little brown birds. Some of these are scrubwrens, of the genus Sericornis (The name ‘Sericornis’ refers to the soft, silky plumage of these birds). Three species of Sericornis live in the forests of Lamington National Park, near my home. Let me introduce you to the Yellow-throated Scrubwren Sericornis citreogularis:
The White-browed Scrubwren Sericornis frontalis:
And the Large-billed Scrubwren Sericornis magnirostris:
When I started birdwatching I found these bird species easy to mix up. But although they are all scrubwrens, and share some similarities, each species has its own unique quirks. Perhaps that’s why they can all co-exist in the same forest patch.
What are some of the traits they share? Well these species tend to be homebodies, not moving very far from where they were born. Records from the Australian Bird Banding Scheme tell us that, on average, individuals of these species move a distance of 1 km between banding and recapture. Even the maximum distance ever recorded for two of these species is very small: 3 km for the Large-billed Scrubwren and 6 km for the Yellow-billed Scrubwren. The maximum recorded distance for the White-browed Scrubwren is larger, at 23 km. But it’s worth noting that many more White-browed Scrubwrens have been banded and recaptured (15616 birds) than the other two species (Yellow-throated Scrubwren: 1016 birds; Large-billed Scrubwren: 1683 birds), so we are probably picking up more of the variation in distance traveled by the White-browed compared to the others.
How long would you expect a little brown bird to live for? Well I am delighted to report that some of these little brown birds live for quite a long time. The maximum age recorded (again by Australian Bird Banding Scheme ) is 15 years for the Large-billed and Yellow-throated Scrubwrens, and 17 years for the White-browed Scrubwren. And the individual birds that set the ‘maximum age record’ for each of these species were released alive after their band details were recorded, so they may have gone on to live even longer.
What about some differences in their lifestyles?
To start with, they all feed in a slightly different part of the forest, and use different feeding techniques.
The Yellow-throated Scrubwren forages mostly on the ground, sometimes in the presence of a lyrebird. Even though its yellow-and-black markings look striking, these colours do provide good camouflage against the similar colours of the rainforest leaf-litter.1
The White-browed Scrubwren forages mostly on the ground too, but it tends to do this within and below dense vegetation.
The Large-billed Scrubwren is more of an acrobat. It forages mainly in the mid-levels of the forest, ‘often spiralling up vines and tree trunks…hanging acrobatically’. 2 Here’s a rough little note I made in 2016 that records this type of feeding behavior:
The nesting habits of these species are quite different too.
The Yellow-throated Scrubwren makes a gorgeous hanging nest, often found dangling over water.
The White-browed Scrubwren makes a dome nest, low among shrubbery or even amongst heaps of debris on the ground. Sometimes they seem to pop right out of the ground on the edge of a walking path, and then you can hear the babies peeping in the well-hidden nest.
The Large-throated Scrubwren sometimes doesn’t bother with making a nest at all. Instead, it will take over the hanging nest of the Yellow-throated Scrubwren (or the similar hanging nest of the Brown Gerygone).
If it does build its own nest, its more of a dome nest like the white-browed, but is built among creepers or vines, or between palm fronds. Or in the dense spiky branches of a bunya pine, like this one in our backyard last May:
The Yellow-throated Scrubwren is also an accomplished mimic, unlike the other two species. Last September I was thrilled to hear one singing its mimicking song for the first time, in Lamington National Park. I heard this little bird perfectly mimic the calls of at least 6 other bird species. But others have heard a male Yellow-throated Scrubwren mimicking 20 bird species in a 30 minute session, and a party of four Yellow-throated Scrubwrens mimicking 26 species.3
Recent work has estimated the evolutionary age of Sericornis scrubwrens using their DNA.4 Below is a phylogenetic tree which shows the estimated ages and relationships between the lineages that have ended up with the species we know today.
Note that this data is not suggesting that the species we see today have remained unchanged for millions of years. Instead, we can say that the White-browed Scrubwren and Large-billed Scrubwren shared a common ancestor about 8.7 million years ago. And that common ancestor shared a common ancestor with the Yellow-throated Scrubwren about 13.3 million years ago. Even though we can say those common ancestors were some sort of Sericornis scrubwren, we don’t know exactly what those common ancestors looked like, or how many different species evolved in the long time period between the common ancestors and today’s species.
Also note that I have simplified this phylogenetic tree a lot by leaving out many other species of Sericornis (there are 11-13 species). I find it fascinating to contemplate that little brown birds similar to the scrubwrens we see today have been frequenting our forests for at least 13 million years. (Remember that humans only evolved about 5 million years ago!).
So next time you spy a scrubwren in the forest, remember that the little brown bird might be older than most school-age kids. Its particular family may have been living in that forest for many bird generations, staying in roughly the same place, and moving far less in each bird-lifetime than you might travel in your daily commute. And its ancestors have been singing, building nests and hopping around on the ground for much, much longer than that.
- Morcombe, M. (2003) Field guide to Australian birds. Revised Edition. Steve Parish Publishing, Archerfield.
- Menkhorst, P. et al. (2017) The Australian bird guide. CSIRO Publishing, Clayton South.
- Higgins, P.J. and Peter, J.M. (eds)(2002) Handbook of Australian, New Zealand and Antarctic Birds, Vol. 6. Pardalotes to Shrike-thrushes. Oxford University Press, Melbourne.
- Norman et al. (2018) Ecological and evolutionary diversification in the Australo-Papuan scrubwrens (Sericornis) and mouse-warblers (Crateroscelis), with a revision of the subfamily Sericornithinae (Aves: Passeriformes: Acanthizidae). Organisms Diversity and Evolution 18: 241-259.