Unlike most native ground predators who are typically slow-moving reptiles (there are notable exceptions such as Quolls and Dingo), aerial predators are usually fast-moving birds who strike their hapless victims at great speed, usually without a hint of warning. Thousands of small songbirds are killed each day across Australia without them ever even clapping eyes on the predator who pummels them. Indeed, aerial predators such as falcons, goshawks, hawks, kites and sparrowhawks go to great pains to avoid being noticed when they’re actively hunting.
That doesn’t mean songbirds aren’t generally always keeping an eye and ear open for the arrival of dangerous aerial predators in the neighbourhood. They are. Always. It’s just that predators, like goshawks and sparrowhawks, are exceedingly good at what they do. Whereas the songbirds they hunt have other pressing concerns (like feeding themselves, courting partners, caring for nestlings etc), predatory birds can afford to remain VERY focused on a singular task.
A case in point – the hunting Grey Goshawk
I’ve watched plenty of Grey Goshawk hunting sessions around here and have discerned that they have a rather particular style of going about their bloody business. They often create a pulse of major flee alarm as birds in the midstory and canopy of the forest first notice that a known dangerous aerial predator has just shown up. The goshawk seems to fully expect this response (murderous psychopaths can hardly expect a warm welcome after all) and typically bunkers down on a fairly inconspicuously located branch to weather wave after wave of very unhappy alarmed birds who have now switched gears into mobbing alarm calls (and sometimes even physical harassment).
Provided the mobbing isn’t too ferocious (eg. if Currawongs get involved it can get a little rough) a hunting goshawk will wait patiently for all the initial alarm ruckus to quieten down, not even contemplating making a run at a dinner ticket during that time. All the freaked-out smaller birds eventually have to get back to their day jobs, which inevitably means taking their eyes off the silent goshawk, even just for a few dangerous minutes (it’s hard to keep watch on a predator when you’re bill-deep in a flower!)
After perhaps an hour of this, when even the most uber-nerdy birdwatcher has grown fidgety and gone back inside the house for a cuppa and biscuit, it’s showtime for the goshawk. If you’re lucky enough to be still watching through binoculars, it’s immediately apparent that the general vibe of the goshawk has changed. Its powerful shoulders now become hunched and those intelligent, sharp eyes take on a notable killers’ focus.
Any songbird worth its salt should immediately recognise this as the unmistakable signal to beat a hasty retreat to the nearest deep-cover of shrubbery. But most are too busy with other business and so don’t realise the escalation in danger until the goshawk is silently bearing down upon them.
That’s normally when I hear the explosive burst of concentrated (proper, life-threatening) flee alarm, accompanied by the sight of dozens of birds falling out of, or through the canopy, as they desperately attempt to evade capture by diving into dense shrubbery where the goshawk is (sometimes) reluctant to follow.
Research on New Holland Honeyeater alarm confirms that perched birds are faster to spot incoming aerial predators than feeding birds (makes sense) and as they rush to hide themselves, they issue an alarm call which front-loads information to other birds about how far away the predator is and how long they should hide for. Even just the sight or wing-beat sounds of nearby birds rapidly moving (in the absence of a vocalised alarm for instance) is enough to create a panicked explosion of evasive manoeuvring as birds seek to find safe refuge.
Furthermore, researchers have discovered that White-browed Scrubwrens and Superb Fairy-wrens vary the complexity of call elements in their flee alarm when reacting to an aerial predator, with the number of alarm elements issued corresponding to how close the predator is. More than likely this is a common alarm capacity across all songbirds.
Alarm is not always a vocalisation, it can also be a non-vocal behaviour such as the sudden silence of White-browed Scrubwren chicks when they hear the tell-tale footsteps of a ground predator (eg. goanna) approaching the nest, or the equally-as-sudden sphere of hush that comes over a section of the forest for apparently no reason. No reason that is until you notice the raven perched in the middle of it. Every nesting songbird in that area of the forest has gone quiet (indicating danger to their chicks in nearby nests) so as to provide the hungry raven with no assistance in locating lunch.
Characteristics of Aerial Alarm Versus Ground Alarm
If I can be crudely simplistic for a moment, I’d like to introduce a VERY broad-brush approach to describing the main difference of sound quality between a ground alarm and an aerial alarm.
As described earlier, ground alarms are issued in response to ground predators and typically consist of harsh, higher pitched notes such as harsh scolding, rasping, crackling and hissing (usually mobbing alarm calls). I call it the “scolding Nanna call” because my Nanna used to make a similar sound on every occasion that she told me off about my dreadlocks when I was a teenager.
It’s important to appreciate that ground alarms are often issued as way of drawing lots and lots of attention (from other birds) to the threat and it’s never hard to locate the author of the call. That is, ground mobbing alarm isn’t meant to be surreptitious. It doesn’t matter if the predator can see the birds making the alarm, the birds themselves have the upper hand since the predator usually can’t fly or jump very high.
Throughout this collective vocal onslaught where a group of birds will get as close as they deem safe to the predator (which can be VERY close with most reptiles), the hope is that the hunter will feel harried and bothered enough to move off to another neighbourhood. At the very least, the alarm has let EVERYONE know about the predator so no-one will be caught unawares. Their babies or eggs in the nest nearby however are rather less safe.
Flee aerial alarm, on the other hand, is typically like an anti-theft alarm on a car. It’s shockingly explosive at first, has an unmistakable urgent quality to it, is low pitched and very hard to place the exact whereabouts of the birds that are making it. In fact, if you reflect on how confounding it is to pinpoint the location of a moving fire truck or ambulance siren, the same is true for aerial bird alarm. All low-pitched sounds have a similar quality of making them difficult to source.
For a Scaly-breasted Lorikeet caught unawares while feeding as a speeding Collared Sparrowhawk enters the scene, the last thing it wants is to spend a few precious seconds sitting stationary in order to issue an alarm that advertises its current whereabouts. That would be suicidal. Step 1 is to save one’s own hide by immediately getting to safety. Step 2 (even if milliseconds behind step 1) is to broadcast an alarm call of a type that not only allows a rapid warning to every bird in the vicinity but also keeps your current location hidden.
Although there are good examples of (very brave) birds such as the notorious Willie Wagtail, who will actually land on the back and head of hunting birds of prey in order to bother them into leaving, the majority of bird alarm you are likely to encounter will be of the sort described here. Its purpose then isn’t to harass the predator but rather to enable an effective and timely ESCAPE.
The Fighter Jet Effect
I bet you’ve had the experience of hearing a sudden and loud eruption of noise somewhere on the horizon which you know from experience is a fighter jet passing low overhead, but instead of looking to where the noise is coming from in real-time, you have to quickly work out which way the sound is moving and then look AHEAD of it if you hope to see the actual aircraft. Aerial alarm can be very similar.
Aerial predators, particularly fast-moving ones, create an intense sonic detonation of cone-shaped alarm followed by a long, receding ‘tail’ of gradually diminishing urgency. Just like the fighter jet scenario, the alarm epicentre will be moving (usually rather quickly) across the landscape so you’ll need to quickly judge the direction of travel and sweep your gaze forward of the epicentre in order to catch the predator at work. In case of a Peregrine Falcon, I’ve had to look at least 100 – 200m ahead of the actual alarm epicentre to see the bird.
The trouble with recording aerial alarm (my endless excuses…)
Ok, so firstly let me confess that I’m yet to actually record a complete aerial alarm exactly as I’ve described above from start to finish. But not for want of trying I assure you. The reason being that, even when you spend thousands of hours in the bush like I do, the probability of carrying sound recording equipment that’s actually turned on and ready (rather than bundled in your backpack) at the exact moment that a peregrine falcon comes speeding across the forest canopy, is…well it’s vanishingly rare. By the time I untangle all the bloody audio cables the show is over.
That’s ok, I’m sure it’ll happen one day and then won’t I be such a happy camper!
That being said, the recordings of aerial alarm I have got are in response to Grey Goshawks. Goshawks are stocky and powerfully built predators whose short, broad wings enable them to pursue birds not just above the canopy but THROUGH and even BELOW the canopy. I’ve personally observed goshawks running (no really – actually sprinting) after my chooks through dense undergrowth that both the chooks and I had previously thought to be goshawk-proof.
I’ve already said plenty on goshawk hunting styles above so I won’t labour the point here, other than to say I had always thought of them as the bird equivalent of a mafia Godfather (ie. unassailable). But I recently came across one splayed out on its back by the road with two ravens standing triumphantly on each wing. It was the first time I had ever seen a look of helplessness on a goshawks face. I was embarrassed for us both.
Aerial alarm recordings
Ok so now take a listen to the alarm calls made by a Pied Currawong (and yes they too can be hunted by Grey Goshawks despite their brawny stature) who has detected a goshawk hunting in its territory and is letting everybody (including me) know. Note here that the currawong’s call is similar to its namesake territorial call (“curr-a-wong”) but with very distinctive changes to the pitch and frequency of the call. The call I’ve recorded is specific to alarm at a Grey Goshawk sitting at perch. Once the goshawk flies, you’ll hear the currawong’s alarm call change notably.
Afterwards some of the surviving birds will signal that the danger has passed through issuing special calls. King Parrots are one of the best examples of this I can think of. Have a listen to this example where a single parrot recovers after an initial scare from a Grey Goshawk passing overhead.
Actually, goshawks are THE most notorious serial killer of our chooks, even taking out large roosters. It is little wonder then the chooks have learned to listen for, and take immediate evasive action upon hearing, the aerial alarm issued by native birds. In particular, our chooks are highly attuned to the aerial alarm warning of King Parrots and male Satin Bowerbirds.
Here’s the sound of a bunch of chooks who failed to heed the warning signs (if indeed any were given on this occasion) of a hunting Grey Goshawk who very nearly took a life that day. Note the initial sudden explosion of alarm is followed by a series of calming vocalisations and how a Spotted Pardalote continues calling without any distraction from either the near-death experience of the chooks or the goshawk (who in any case probably couldn’t be bothered with such puny prey):
Aerial Alarm Sequences
If you want to see more goshawks, falcons and other cool birds of prey as they hunt over your sit spot, you really do need to start paying attention to aerial alarm.
Over the years of observing aerial alarms around here I’ve come to recognise that there are very coordinated multi-species alarm sequences at work. The most notable is that of the Pied Currawong – King Parrot – (male) Satin Bowerbird trio. Mostly it’s the sharp-eyed currawong who spies the danger first and issues a general-quarters warning that a goshawk is in the locality. Once it locks on, the currawong will track the goshawk across its entire territory for hours.
Next comes the explosive, metallic clanking alarm of King Parrots as they squirt out from the forest travelling directly away from the oncoming threat. It is unclear to me whether the parrots actually SEE the goshawk themselves or are instinctively reacting to the currawong alarm calls. Whatever the case, they’re certainly in a huge hurry to get the heck out of there.
Last comes the long, descending cry of the male Satin Bowerbird, often repeated twice. There’s no way whatsoever that the bowerbird, ensconced down there in the dense shrubbery of the gully where he fusses endlessly over his bower, could possibly have got eyes-on the goshawk. He’s reacting purely in response to the King Parrots and / or currawong.
The effect of all three is like that of a police APB – everyone knows who’s coming and what that means, especially me – I will drop whatever I’m doing and rush out onto the veranda to get a glimpse of a potential goshawk attack drama. Usually I’m trailing a tangled mess of leads and half-assembled recording equipment.
It’s devilishly hard to get a recording of the whole trio alarm sequence – they happen so infrequently and without any warning – but I have managed to capture King Parrots alarm triggering the Satin Bowerbird. Have a listen:
And here’s a bunch of King Parrots being scared out of their brains after a Pied Currawong initially raises the alarm when the Goshawk cruises into the valley on a kill mission. After they begin to settle down (at a safe distance away) a Satin Bowerbird takes up the cause with its harsh hissing alarm.
See also Ground alarm
Next page: Territorial