Friday, 20 January 2012

Extraordinary feral pigeons

ResearchBlogging.orgWhen I make bird lists I do not often tick feral pigeons (Columba livia). They are always there, but I like to take photos of their behaviour.
The local flock sitting on the roof, waiting for the sun to rise in the morning,
 the flock scared by a movement or noise, suddenly taking off and flying in a few elegant circles before settling back; a few of them feeding on the bread that some old lady dutifully brings to the same corner of the street each morning; males in display flight holding their wings high in a V pattern and gliding in a circle.
Their leisure times, having a bath...
...or enjoying the sun on a cold day
Despite their ubiquity, feral pigeons are still extraordinary birds. They are descendants from the Rock Dove, a wild bird of river canyons and sea cliffs, domesticated millennia ago. Some have now have returned to the wild, although still quite attached to humans. Some feral pigeons (above) have very similar plumage patters to their wild ancestor: bluish grey, with a double black wing bars and iridescent neck. Many also keep a trademark white patch in their rumps (like the one bathing on the photo above).

Charles Darwin extensively bred many domestic pigeon breeds and dedicated a sizeable section of the first chapter of the Origin of Species to domestic pigeons. He used them to illustrate how domestication had generated distinct races through breeding together animals with certain preferred variations, producing a wide array of diverse shapes, colours, plumages, flight ability and voice from the original ancestral species, the wild Rock Dove. He stressed that this "selection by man" was essentially the same mechanism that his "natural selection".

 Male pigeons court females by cooing and bowing to them while walking alongside her with puffed feathers, inflated necks and fanned tails, pirouetting occasionally. The courting male, on the left, is also showing his white rump patch.
 A quick copulation may ensue...
 As other pigeons, Feral Pigeons lay two eggs per clutch. They nest on ledges inside abandoned buildings, inside roof spaces where they can gain access, or outside, under bridges. Fledged squabs, the young birds (below), have dark eyes, underdeveloped operculum - the white swelling a the base of the beak - and have a look of naivety about them. Both siblings often move about together.
Although mortality, even in town, is high. According to research by Alberto Pelleroni and colleagues, the wild-type blue plumage with a white rump affords a survival advantage to feral pigeons, as it decreases the chances of success in Peregrine Falcon attacks. When pigeons with and without the white rump patch had their feathers swapped, the success of the Peregrines reversed accordingly. The presence of Peregrines in the area increased the frequency of the feral pigeon wild type in the area. As for the possible reason for the increased failure of Peregrines in capturing wild-type feral pigeons:

All feral pigeons perform the same evasive roll during predation by falcons. The protective white patch may disguise the initiation of the pigeon’s evasive roll by contrasting conspicuous (white patch) and cryptic targets (grey wings and body). A fast flying falcon primed to a conspicuous target centered on the roll might fail to detect the dodge initiated by the cryptic wings as the predator closes from behind.

 I wonder who ate this squab? Sorry if you are squeamish!
Never underestimate pigeons. They have been found to outperform university students in a range of probability calculation tests (see this post for an example). According to Walter T. Herbranson and Julia Schroeder:
Pigeons might not possess the cognitive framework for a classical probability-based analysis of a complicated problem [...], but it is certainly not far-fetched to suppose that pigeons can accumulate empirical probabilities by observing the outcomes of numerous trials and adjusting their subsequent behavior accordingly.
Update: see this post on pigeon convergence


Herbranson, W. & Schroeder, J. (2010). Are birds smarter than mathematicians? Pigeons (Columba livia) perform optimally on a version of the Monty Hall Dilemma. Journal of Comparative Psychology, 124 (1), 1-13 DOI: 10.1037/a0017703

Palleroni, A., Miller, C., Hauser, M. & Marler, P. (2005). Predation: Prey plumage adaptation against falcon attack Nature, 434 (7036), 973-974 DOI: 10.1038/434973b

1 comment:

  1. I've often wondered about the lifestyle of city populations of pigeons versus those in less industrialized areas, and whether a steady diet of mankind's fatty scraps (and polluted environment) over generations has created yet more evolutionary divergence. Do you know if anyone has conducted a thorough study of the differences between city birds and country birds?