Sunday, 2 October 2011

Pigeons Everywhere

If you visit Rio for the World Cup or the Olympics you will see many beautiful and exotic sites, but one very prosaic one - pigeons. Even on Copacabana you will not see the ubiquitous seagulls of Northern Europe, but pigeons picking at the remains of ice creams and sandwiches left by tourists. They seem to quite like resting on the sand.

A pigeon on Copacabana beach

Brazil has various "pigeons", for instance the little Ruddy Ground Dove, but here we are talking about the Rock Dove (Columba livia), one of the most successful species in the world. They probably evolved in South Asia, but spread rapidly, fossil evidence showing that they have been in Israel, for example, for over 3,000 years. The first recording in the Americas was in 1606, in Nova Scotia, and they were later introduced through the Americas as domesticated birds. They are now virtually ubiquitous in towns and cities in Brazil - a recent study in the southern city of Porto Alegre found them to be the 2nd commonest bird, after house sparrows.

Why so successful?

a) Tolerance
Man isn´t always tolerant of pigeons, especially when they are eating his crops, but pigeons are extremely tolerant of man. How many other birds would by happy in the noise and confusion of Trafalgar Square? This allowed their domestication early in human civilisation, but also opened up a world of opportunity for wild pigeons. It didn´t hurt that cities are, to a pigeon, very similar to the cliffs their ancestors evolved in, so there are plenty of nest sites.

Pigeons on a castle wall in Tonbridge, England

b) Adaptability
Pigeons are the dogs of the bird world, in the sense that they have a huge potential for variation. Darwin noted this, devoting a whole section in the first chapter of The Origin of Species to differences in domestic pigeons - "the variation of the breeds is something astonishing" although "I am fully convinced that the common opinion of naturalists is correct, namely, that all have descended from the Rock Pigeon (Columba livia). "

So pigeons are adaptable, especially in....
c) Food
Pigeons are basically seed eaters, but as everyone knows, they will eat more or less anything. This is one of the reasons for their success, and results from a very forgiving digestive system which can cope with high carbohydrate or high protein food.

d) Temperature
How on earth can the same species be happy on a scorching Copacabana beach at 40 C and a bitterly cold English city at 0 C?

Pigeons in Reading, England in February. Happy?

The wonderful adaptability of pigeons spreads to thermoregulation, so that they can adapt themselves to temperatures even up to 60 C.
"Normal" birds will pant to lose heat, but adapted ones evaporate water from their skin. It´s not sweating as such, but they actually change the structure of their skin so that it has a much greater blood supply and is more hydrated. On the other hand, in the cold pigeons form an extra layer on their skin to stop evaporation, as well as eating even more than normal. Actually, pigeons prefer it warm as they can spend less time brooding baby pigeons and more time feeding (and so make more baby pigeons).

Flying rats?

It has to be said that communal nesting and a lack of delicacy over food does come at a price. Concerns have been raised over the hygiene, of pigeons, given that guano tends to be a prominent feature of their local environment. For example, 10 out of 33 pigeon droppings studied in in the city of Vitoria had Cryptococcus neoformans, a cause of fungal meningitis. On the other, these were old, dry, droppings, and the birds themselves when examined, er, intimately, they did not have the fungus, nor did other ones in Fortaleza. In other words, the guano had not been cleaned away and was just somewhere for the fungus to grow. So it could be argued (perhaps not very convincingly) that this is a lack of human rather than pigeon hygiene.

Pigeons probably do itch quite a lot. A study of 14 nests in the city of Manaus in the Amazon collected over 10,000 arthropods over 12 days, mostly mites. This was actually less than would be found in other parts of the world, probably because the local parasites have not quite adapted to pigeons yet.

How to have less pigeons

A pigeon having a drink on Copacabana

Various raptors will take pigeons. They form a large part of the diet of the Black chested buzzard (Buteo melanoleucus) and are taken by the Stygian owl (Asio stygius) and other hunters, but this is not exactly a control strategy. Spikes or wires to prevent perching work well locally, but just shifts the problems. The fashionable solution at the moment is bait treated with a contraceptive, and this is now being used around the world. A study in Ljubljana, Slovenia, found a 24% reduction in numbers over 3 years. Interestingly, the pigeons that remained were healthier, with fewer parasites.

But the problems of urban life not withstanding, pigeons have been valued by the Egyptians, the Romans, and rulers of ancient India and Iran through history, and they are one of the most successful species on the planet. Perhaps we should pay them a little more respect.


Anonymous said...

My God! So many things! Very interesting!

sw said...

They do have their uses. This is very good.

Not sure that I fancy eating a tree rat but you can buy domestically raised pigeon meat in the UK.

Now there is and idea for Brazil: pigeon farming.