At WiseGEEK, we're committed to delivering accurate, trustworthy information. Our expert-authored content is rigorously fact-checked and sourced from credible authorities. Discover how we uphold the highest standards in providing you with reliable knowledge.
Looking up in the sky and seeing a flock of birds temporarily obscuring the Sun can be an awe-inspiring sight. But while you may have seen flocks containing hundreds or thousands of birds – or even a million in a murmuration of starlings – that's nothing compared to one particular flock that darkened the skies over southern Ontario in 1866.
Once the most common bird in North America, passenger pigeons gathered in such large numbers that one flock is thought to have contained 3.5 billion birds. The size of that flock was truly mind-boggling, stretching over a mile wide and 300 miles long, and taking 14 hours to pass overhead. Incredibly, the passenger pigeon would be extinct by 1900, due to over-hunting and habitat loss.
Believe it or not, another 19th-century event dwarfs the 1866 passenger pigeon flock. In 1875, physician and meteorologist Albert Child witnessed a swarm of Rocky Mountain locusts that he estimated contained around 3.5 trillion insects (though some estimates say 12.5 trillion). "Albert's Swarm" covered some 198,000 square miles (512,800 square km), darkening much of the western United States. Incredibly, just like the passenger pigeon, the Rocky Mountain locust is now extinct, despite these inconceivably large numbers.
Strength in numbers:
- Atlantic herring are thought to gather in schools containing up to four billion fish.
- The red-billed quelea of sub-Saharan AFrica is thought to be the world's current most populous bird, with flocks sometimes containing millions of members.
- While mammals can't compete with birds, insects, or fish in terms of group size, they can still come together for some pretty impressive gatherings. Herds of springbok and wildebeests on the African savanna can contain around a million animals, while one cave in Texas is home to some 20 million Mexican free-tailed bats.