Brown Goshawk – Accipiter fasciatus

I was recently treated to this sight in our home paddock – a Brown goshawk with an unfortunate Tawny frogmouth that it had just killed.

Brown goshawks are widely distributed throughout Australia, but favour timbered areas where they can perch and look for prey. Their favourite diet is in fact other birds, but they will also take reptiles, mammals and large insects as well. At breeding time they have been known to attack humans.

I’m fairly certain this individual lives close to me, based on other sightings in a nearby National Park. Over the last few years we have lost a number of chickens, and this is almost certainly the cause. But rather than blame the bird we have erected a shade cloth to deter its approach – and just accept this is nature. It’s a sign of a good ecosystem to have apex predators present, and we are fortunate to have this one in the area.

Brown goshawks are also famous in ornithological circles for how similar they are to Collared sparrowhawks. There’s a number of Australian bird species that look almost identical, and these are probably the worst (or best) at it. However there are some subtle but important differences. The easiest to notice is that the deep set eyes and prominent eye-brow ridge of the Goshawk make it look like it is glaring, whereas the Sparrowhawk looks like it is staring. There are other skeletal and behavioural differences as well, and these could be caused by a number of processes, but I believe they are most likely a result of sympatric speciation – where part of the gene pool heads in a completely different direction and eventually becomes a new species. This is evolution occurring right before our eyes – but remember to stare at it, don’t glare at it!

This article first appeared in the High Country Herald on 6th of May 2024

Here’s some more I wrote about the relationship between Brown goshawks and Collared sparrowhawks on the BSQDD blog:

What’s going on with these birds is an example of sympatric speciation. This is where you have one species and a segment within that species starts going its own way genetically. This can occur for a number of reasons but it’s not due to the population being separated by a geological event – that’s allopatric speciation.

A great example of that is in New Zealand. Originally there was what’s called proto-Kakas, which were the forebear of both the Keas and Kakas there now. When the mountains formed in the South Island (about 5 millions years ago) it split the proto-Kaka population and eventually gave rise to the Kea and Kaka that we know today. But this is allopatric speciation, the Collared sparrowhawks and Brown goshawks are sympatric speciation.

They both occur throughout Australia across a variety of habitats – there is no natural barrier separating the populations. Without reading any genetic studies, because the Collared sparrow hawk has slightly more specialised feeding habits, and because there are 3 subspecies of Brown goshawk recognised, but none for the Collared sparrowhawk, I would suggest that the Brown goshawks are basal and that the Collared sparrowhawks are an offshoot from them, rather than the other way round.

What constitutes something being different enough to be its own species is always up for debate. The more you drill into the biological species concept the less it stands up. ie one species can’t interbreed with another one and produce viable young. There are exceptions to this, and there may also be instances where populations believed to be different species could in fact interbreed and produce viable young but we don’t know because the populations are so far apart (and this could be in time as well as space), so the usefulness of this definition breaks down. It is interesting to consider that since many people have some Neanderthal DNA in them – Homo sapiens and Homo neanderthalensis can’t be different species under the biological species concept.

This leaves what is called the phylogenetic species definition – which is a combination of the morphological and evolutionary ones. The morphological species definition is based on morphological and biomechanical similarities; and the evolutionary one is based on genetic similarities and the likelihood of common ancestors. These can both be used to determine how similar or different animals can be; and then these definitions can be combined to give us the phylogenetic species definition. This tells us where a species sits in its evolution and classification in relation to others. Hence phylogenetic trees.

Bad photo of a Collared sparrowhawk taken on a really really really really long zoom lense

The morphological differences between the Collared sparrowhawk and Brown goshawk are enough to define them as different species under the morphological species definition, although they are obviously extremely closely related. Hence a recent speciation event I believe, and the main reason why there are no subspecies of the Collared sparrowhawk ie there hasn’t been enough time for them to evolve yet, but there has been with the Brown goshawk. It is also logical then that Collared sparrow hawks are the descendants of the first subspecies of Brown goshawks to evolve, and that they continued their own evolution far enough to eventually to be distinct enough to be their own species.

The habits and behaviours of these birds are now enough to keep the populations separated as well, and I’ve found no records of them hybridising, though I have with the Brown and Grey goshawks.