“Singapore’s Health Promotion Board spends a lot of time telling people what not to eat. And zoologists keep harping on the ill effects of plastic if it is swallowed by seabirds and other types of animals.
“However, the Rock Pigeon (Columba livia) obviously does not believe in health warnings. Some I know enthusiastically eat large amounts of plastic, with no apparent ill effects.
“A number of styrofoam storage boxes are stacked on my back porch. Rock Pigeons have taken to pecking at the flat surfaces, breaking off the individual beads of plastic, and actually swallowing them.
“I am woken every morning, by the sound of Rock Pigeons drumming as they perch on the resonating boxes and peck away.
“This has been going on for a while. I can recognise the same ones that arrive each day. They all seem to fly and walk as well as any other birds that I have ever seen.
“While I will extend some theories as to why they remain healthy, I (and I am sure our webmaster also) would welcome any other opinions as to what really is going on.
“First, the Rock/Domestic/Feral Pigeon is highly intelligent, daring and willing to try anything. These qualities have helped it to survive despite all efforts by the Agri-Food and Veterinary Authority and the National Environmental Agency to exterminate them in Singapore.
“Their innate curiosity might have caused the Rock Pigeons to first pick at loose bits of styrofoam on the boxes, and finding that the taste is appealing (why I don’t know), start swallowing them. The flavour might have encouraged them to actively damage the boxes to dislodge more bits.
“Alternatively, as some people love to spend time popping bubble wrap, as with other intelligent birds that sometimes appear to carry out actions just for the intrinsic fun of doing things, these Rock Pigeons might be engaging in vandalism just to relieve boredom.
“But while seabirds keel over and die when they ingest too much plastic, in the weeks that this destructiveness has been going on, the Rock Pigeons still appear fit and strong.
“My theory, for which I would welcome alternative views, is that the digestive systems of these pigeons are different from those of seabirds.
“I do not have much experience with raising seabirds, only having kept the Chestnut (or Cinnamon) Bittern (Ixobrychus sinensis) and the Little Heron (Butorides striatus). But I do know that they have short digestive systems designed to cope with high-protein prey containing relatively few impurities. When plastics get into the system, they stay there, cause congestion, and the eventual death of the bird.
“The dietary requirements and habits of Rock Pigeons and their relatives in the family Columbidae have been very thoroughly documented in the literature of aviculture.
“Unlike parrots and finches, pigeons do not shell seeds before swallowing them. Their guts are designed to cope with, and expel, things that cannot be digested.
“Seeds are swallowed whole. To break through the tough husks and casings, birds of this family also ingest large quantities of grit, some of it comprising bits of seashells, gravel and ceramic with jagged edges. The mass of seeds and grit is churned in a muscular, thick-walled crop until the husks are broken through and the kernels are exposed for digestion.
“The mass of grit, seed husks, seed kernels and sometimes plastic passes through the alimentary canal, where the nutritious parts of the intake are absorbed, and the considerable amount of undigested bits is passed out, much to the chagrin of the Town Councils tasked with building maintenance.
“Through my experience in cleaning aviaries, I can vouch that pigeon droppings are exceptionally messy when compared to those of other birds.
“It has been recorded that even glass and metal bits have been broken down into smaller pieces after passing through the guts of certain seed eating birds.
“It would appear that anything that is not outright toxic can pass through a Rock Pigeon without causing long-term ill effects. I would assume that ingested plastics would also be eventually passed through.
“The Rock Pigeons are still doing their best to demolish my storage boxes, which are considerably the worse for wear, but which is not the case with the birds, unless I decide to beat them up.
Lee Chiu San
16th December 2018