A suburban street in Mexico with dead blackbirds scattered around. What happened?

It was none the obvious causes: chemicals, shooting, lightening, an aircraft, or even aliens. Understanding the cause first requires a diversion.

Murmurations are large flocks, usually of starlings, that gather around sunset above their roosting sites. There, they twist and turn into fantastical shapes – they even may fold back and through each other. Click on the image to see a spectacular video.

This remarkable attribute has just one cause – raptors utilising their starling’s returns to seek an easy dinner. The birds gather in huge numbers to reduce the danger to each individual. They also have learnt to respond to an attack with a simple tactic. In addition to watching for predators: all converge towards each other and then maintain a minimum separation distance, and each one monitors the flight of its seven nearest neighbours. When one sees an incoming predator and changes direction, its neighbours respond instantaneously. Their neighbours respond similarly, and a high-speed ripple passes through the flock.

The term ‘murmurations’ arose from the noise modulation from the rapidly flapping wings as the flock changes direction.

Similar processes drive the movements of large shoals of fish as they gather, then manoeuvre to avoid predators.

Back to our dead birds. The cause appears to be that this flock was too close to the ground when a predator appeared. As they responded, some plummeted at full speed into the hard surface. Their lucky neighbours either bounced, or turned away in time to prevent the destruction of the entire flock.

Click here to see a video of the full sequence.

Many other animals respond to a perceived danger in similar ways, even humans. A sudden movement in a crowd may lead to a panic response as everyone surges without even knowing why. The resulting mob has been known to trample those that have fallen, and crush those caught against walls or narrow openings. In 1982, three aircraft in the Thunderbirds Aerobatic Team were following their leader in a formation loop. All four crashed into the ground at high speed and the subsequent inquiry concluded that the crash “was due to a jammed stabilizer on the lead jet. The other pilots, in accordance with their training, did not break formation“!

– Article by Greg Holland, first image from here