Passenger Pigeons were observed breeding in single pairs and flocks of dozens during the 1800’s. The idea is that Passenger Pigeons evolved to live in huge flocks and became dependent on their large flocks, meaning they could not produce enough offspring to survive unless there were billions of them, either for social reasons (they would not breed in small flocks), for predator reasons (they could not satiate predators without huge flocks), or for resource reasons (they could not find adequate food sources in small populations).

While contradictory to the first, both misconceptions are often cited in the scientific and popular literature. Our current population genetics analyses show that the Passenger Pigeon was stably abundant for tens of thousands of years, before humans arrived in North America. In fact, using the same study technique, another analysis found that Passenger Pigeons were abundant in the Southeastern United States prior to European arrival. The factsĪrchaeological remains do not reflect population sizes accurately the only thing they indicate reliably is the presence of a species during a given time period. The hypothesis devised to answer this conundrum was that: 1) Native peoples competed with Pigeons for acorns and other nuts, keeping their numbers in check 2) The genocide of Native people through warfare and disease after the arrival of Europeans to North America relieved competition for acorns, allowing the Passenger Pigeon population to boom. By comparison, Turkey and other bird remains were more numerous than pigeon bones in historic Amerindian village sites. The assumption was that if there were billions of Passenger Pigeons in the past there should be many bones. This idea arose in the 1980’s to address the seeming lack of Passenger Pigeon bones in archaeological sites in the northeastern United States. Tail shape also affects flight maneuverability, an important factor when flying only a few inches from dozens of other birds at speeds over 60 miles per hour. The graduated tail of the Passenger Pigeon was likely also used in courtship displays and influenced mate choice.

The red breasts of males were likely a signal of superior fitness to females seeking the best mate in a crowd.

The birds’ appearance may not seem important to the Passenger Pigeon’s ecological function, but a bird’s plumage is key to how mates are chosen in social flocks. Male and female Passenger Pigeons looked different, which is a rare trait among the world’s more than 350 species of pigeons and doves. This rapid growth meant that breeding Passenger Pigeons could leave nesting sites quickly before exhausting the local food supply. Passenger Pigeon hatchlings grew up rapidly and were able to fly in 14 days, half the time required by Band-tailed Pigeons. The Passenger Pigeons’ hyper-sociality wasn’t only facilitated by behavioral traits morphological and physiological traits were a key part of the birds’ adaptation to high social densities. There are historic accounts of roosting pigeons bending the crowns of young trees down to the forest floor under their combined weight. When roosting, they were so hyper-social that the birds would line branches perched shoulder to shoulder and even sit on each other’s backs. Unlike Band-tailed Pigeons, which will nest in densities of one nest per three to four acres, Passenger Pigeons nested in densities of up to 100 nests per tree. The Passenger Pigeon lived in dense flocks because of a unique behavioral trait: their social breeding.

Passenger band