Alarm

Bird alarm generally falls into two broad categories of predator response – ground predators and aerial predators. As a general rule-of-thumb, birds that nest and forage close to or on the ground will go absolutely nuts about ground predators like goanna but not necessarily be overly concerned about a passing bird of prey. On the other hand, birds who nest higher up in trees, or just spend most of their time foraging up higher in the forest will be most worried about aerial predators and not care so much about a basking python on the forest floor.

Keep in mind that this description is a handy generalisation only. For instance, even though Laughing Kookaburra spend much of their time in the midstory or canopy of the forest (coming to the ground only to pounce on prey) and nest in arboreal termite mounds high above the forest floor, they’re most notable and forcible alarm response is directed at goannas (a ground predator who climbs).

Goanna are incredibly effective nest raiders. These wily reptiles can sniff out a Kookaburra nest from tens of metres below, which they happily climb to and devour the young or eggs. The only thing that dissuades them from this wicked endeavour is the sensation of multiple bill-beatings from angry Kookaburra. Even so, they often just weather the violent blows and soldier on regardless.

Alarm calls (both aerial and ground based) can be either non-life threatening to the caller (‘mobbing’ alarm calls), or immediately life-threatening (‘flee’ alarm calls). For instance, when a noisy miner discovers that a grey butcherbird has entered the area, it doesn’t personally feel that its’ life is in peril (so doesn’t need to immediately flee), rather that the butcherbird is a known nestling-eater, so the miner begins making its whining, annoying mobbing call.

Other miners hearing this call are recruited to the task of annoying the poor butcherbird and fly in to add their voices to the cause. After perhaps a dozen or more miners have gathered into a mobbing-call gang, the exasperated butcherbird will get the shits and move off to somewhere quieter (like joining me while I chainsaw firewood!).

So mobbing alarm calls are about bringing attention to the discovery of a not-immediately-life-threatening predator with the aim of annoying said predator to such an extent that it departs the scene. Mobbing can also be performed while on the wing and reinforced with pecking, dive-bombing or other aerial harassment (such as a willy wagtail landing on the back of a soaring wedge-tailed eagle). Furthermore, mobbing alarm is VERY effective.

There is a distinct difference in the quality of sound made by a mobbing call relative to a proper alarm call. Generally speaking, mobbing calls are whiny, persistent across multiple minutes and annoying (to us and the predator). Mobbing callers (mobsters?) are also usually very visible – ie. they aren’t trying to hide from the predator.

On the other hand, full-blown flee alarm, such as when a honeyeater suddenly detects a hawk bearing down on it from on-high, is usually explosive, front-loaded for immediate communication effect, of very high intensity and urgency and quickly diminishes into silence or calming notes over the duration of a minute or so. Birds faced with the prospect if imminent death aren’t mucking about when they issue a flee alarm call. It’s a serious business, with the prospect of being torn asunder by sharp talons or beak only a matter of fractions of a second.

Birds issuing a flee alarm definitely want to avoid being seen by the incoming predator so take urgent action to hide, even while calling. This is why you’ll HEAR the alarm but rarely SEE the alarmer.