Author: Nina Gibson
Illustrator: Nyla Binti Norhafiz
The feral pigeon: a staple of the streets of London and many other cities across the world. While many animal species decline at alarming rates globally, these birds stay resilient to the effects of human activity. This raises the question: do pigeons hold the secrets to modern animal success?
From messengers to government spies, pigeons have been integrated into human activity for millennia. Feral pigeons (Columbus livia) are the bird species most commonly found in cities, descending from pigeons first domesticated for use as a food source. Today, free from human employment, they have acquired new talents such as chip-stealing and commuting on the underground. And yet, even with these somewhat unusual habits, they manage to thrive.
Mass habitat destruction means abnormal animal migration is becoming more frequent. Coyotes, wild boar and even mountain lions have been found traipsing through cities worldwide. Establishing the reasons behind the success of the feral pigeon might provide insight into whether other animals could settle in our urban jungles. Let’s take a closer look.
Picking at a half-eaten sandwich on the side of a road, while maybe not ideal, is not at all alien for a pigeon in the city. Digestive flexibility is essential for urban success and is likely permitted by favourable enzymatic activity, which allows for the efficient digestion of a variety of scraps.
To find these scraps, they have another trick up their sleeve: pigeons have an incredible homing sense, hence their historic use as carrier pigeons. This means they can travel as far as 5km from the city in search of their next meal, and then effortlessly return to their flock using the sun as guidance. But given how frequently overcast London is (don’t we all know it), sole reliance on the sun for navigation seems questionable. Pigeons do not simply stop foraging on a cloudy day.
A recent study by Lisowski et al. on Columbus livia explored potential mechanisms involved, finding something quite impressive. Old red blood cells, when engulfed by macrophages (a type of white blood cell), release billions of iron atoms. They found that liver macrophages in pigeons do not store this iron in a disordered fashion as expected; instead, they densely pack it into highly organised crystals. These crystals rearrange in response to changes in magnetic field intensity, transmitting signals to adjacent nerve fibres to inform the pigeon of direction.
Animals such as bees and sharks are known to navigate using Earth’s magnetic field, so this is not a new phenomenon. But the direct involvement of the immune system in navigation has never been seen before – pigeons really do hold some secrets.
Expert navigation allows pigeons to exploit many food sources, complementing their dietary flexibility. What’s more, cities closely mimic their ancestral habitats, with a nook in the roof of a Travelodge being quite comparable to a ledge in the side of a rugged cliff. And so, feral pigeons have happily called cities like London home.
Compared with the brown rat (another highly successful urban species), we see similarities in traits such as diet and habitat flexibility, indicating these are critical to thrive in cities. But there are significant differences too. Rats, alongside most other city dwellers such as foxes and raccoons, are nocturnal. This means they mostly avoid human interaction.
A 5000-year head start in human interaction due to domestication means pigeons are comfortable in close proximity to humans (even if we don’t feel the same way). As few animals have this kind of history, it is unlikely that migrating animals would be suited to the busy daytime, confining them to the night to find a niche.
With growing agriculture and rapid urbanisation, wild animals are running out of space and being forced into cities. Unveiling the ecological secrets of the feral pigeon provides us with a unique perspective on who might stand a chance. Being highly adaptable is certainly required. However, there may be a bit of leeway for daytime living – provided, like the pigeon, you have a built-in liver compass and are happy around humans. With such strict criteria, let’s see who else can pass this urban test.