On Saturday of January 7, we watched HM and HD respond to alarm calls issued by the local neighborhood crow watch. Alarm calls convey information with pitch, volume, bandwidth, repetition, duration, inflection, and sound. Most of us are familiar with a chickadee’s ‘chick-a-dee-dee-dee’ alarm call: a social signal that tells other chickadees to rally in the vicinity of the predator – usually a perched bird of prey – and join in a chorus or mob of calling. The number of ‘dees’ conveys information about the urgency of the threat, with closer or more dangerous predators earning the most dees.
Sound the Alarm!
The sonogram below was captured by a recordist. A chickadee spots him and responds with three dees – a not-uncommon response to humans ambling through chickadee territory. We’re unusual but, unlike screech owls, not especially dangerous to chickadees. The response changes almost immediately after the recordist imitates a screech owl. The chickadee rapidly responds with eleven dees (danger! danger! danger!) and moves in closer, calling other chickadees to join it. By a minute into the recording, the woods are ringing with alarmed chickadee calls and everyone knows that a raptor is perched near by. The alarm can propagate at speeds exceeding 100 miles per hour, giving birds plenty of time to take cover, join the mob, or – as we’ve seen our eagles do in response to crows – issue their own warnings. The jig is up and the predator might as well move on.
Perched raptors are potentially dangerous, but raptors on the wing are an immediate threat. Seets or zees are short, high-pitched, narrow bandwidth calls that warn of a raptor in flight. Instead of mobbing, small birds duck into cover or freeze. See the lower volume and narrower bandwidth? That makes it harder for the hunter to tell where calls are coming from. More than 50 different species will respond to a chickadee’s mobbing and seet calls, including species that don’t live in chickadee range. Seets are a universal alarm call among birds and small mammals worldwide.
Check Your Facts!
Some species verify mobbing calls before responding to them. Mobbing or fleeing might result in a missed meal or interrupted courtship, which can have serious consequences for a bird’s health and/or reproductive success. When red-breasted nuthatches hear predator calls directly, they issue their own mobbing call – a series of rapid, single-syllable chirps – to communicate specific information about the threat to other nuthatches. But when nuthatches hear chickadee alarm calls, they issue a vague warning until they see or hear the threat themselves. Why? Some species deliberately issue disinformation to frighten others away (blue jays imitating hawks, for example), while others seem more likely to unintentionally spread misinformation. ‘Rumors’ might be more easily spawned in a highly gregarious species like black-capped chickadees. The recordist certainly fooled them!
A blue jay imitates a red-tailed hawk
Eagles and Crows
Our eagles behave a lot like red-breasted nuthatches when it comes to crows. When Mr. North, DNF, HD, or HM hear a group of crows cawing, they stop everything and look for the source of the alarm. If the crows are signaling a threat – a red-tailed hawk, another bald eagle, or an owl – the eagles might respond by issuing their own warning (we see you) or flying out to drive the intruder away. If the crows are vocalizing about carrion, the eagles might swoop in to grab it. And if the crows are talking to other crows, the eagles will largely ignore them, although they might keep their ears and eyes open just in case something changes. Crows and eagles aren’t in a mutualistic relationship, but an eagle’s territorial behavior might benefit crows at the cost of a meal or two.
The woods are full of aural information: complex warnings, gathering instructions, love songs, and territorial claims. Open your ears and the next time you hear crows, chickadees, red-breasted nuthatches, blue jays, or titmice sounding an alarm, take a look at what they are calling about!
Did you know?