The Role Of Pigeons In Scientific Researches
Pigeons belong to the family of Columbidae, which entails both pigeons and doves. Although people often believe there to be a distinct difference between both such as colour, in reality this is nothing more than a misconception as both names are interchangeable. Columbidae are vertebrates belonging to the class of aves (birds). There are 310 known species of Columbidae, ranging from the size as we all know, to ones as big as turkeys.
To specify further, they belong to the order of columbiformes, the genus of Columba and we will focus specifically on the species of Columba livia, which is commonly known as the domestic pigeon. Noticeable is that pigeons are socially monogamous and therefore mate for life, although extra-pair mating does happen sometimes. Already 4000 years ago, pigeons were bred for their unique feature, namely homing. This is ‘the ability to return to the home flock from an arbitrarily chosen unfamiliar starting point located up to some hundreds of kilometers away’ (Güntürkün, 2014).
Even in the Second World War, thousands of pigeons were still used to send messages and many pigeons were decorated for bravery afterwards. (Günterkün). The Columba livia was originally found in Europe, Northern Africa and India and was called the rock pigeon (as it had not been domesticated yet). Around the 17th century, early settlers introduced them into the Eastern part of the United States as domestic bird and started to mass-bread them for its homing feature. Many Columba livia escaped and quickly spread to the whole of North- and South-America. Remarkably, the domesticated pigeon kept its adapted behaviour to the human and therefore is currently most often seen in urban environments all around the world.
However, the increase in numbers of the entire Columbidea is not as prosperous as of the domesticated one. The Columbidae is on of the most threatened bird families in the world, due to human persecution, introduced predators and habitat loss. Although they can be found in every continent except Antarctica and live in habitats as diverse as tropical rainforests, deserts, mountains and cities, fifty-nine species of Columbidae (of the 304 species) are currently being threatened. Most threatened Columbidae live in Asia and Oceania.
Pigeons are excellent organisms for research, mostly due to the fact that they have been domesticated for centuries. As a result, adult pigeons can easily adapt to human handling. They can be touched by both familiar and unfamiliar individuals without having to be hand-raised (contrary to birds such as magpies and crows). Because these animals were already present in the everyday life of many people, it was easy to introduce them into their research. As a result, the Columba livia already was used as an experimental animal in the nineteenth century. (Güntürkün et al., 2014). However, this species has many more advantages, especially for the cognitive function model.
According to Güntürkün et al. Pigeons have a very long life span, compared to animals previously used for animal testing. "Pigeons [...] may live up to 20 years in captivity", (Güntürkun et al., 2014). This characteristic is very important for cognitive testing, because the training takes a certain amount of time and the problems are very complex. If the animal dies after 2 or 3 years, it is very complicated to study complex learning processes. Moreover, pigeons have a very good developed visual system (Pigeons have 2.3 times more nerve fibres than humans), they are devoted to work with humans for hours without resisting and they are able to perform difficult cognitive tasks.
Pigeons are willing to work with humans, they don't frustrate as fast as other animals and like to work for a long time, several hours even. They don’t show any "aggressive behavior"."Skinner claimed to have trained a pigeon to peck 35,000 times on a pecking key—for merely half an ounce of grain." (Güntürkün et al., 2014)If we look at the pigeon’s cognitive capacity, it is astonishing to see their skills in cognitively demanding tasks. They can be trained to remember hundreds of pictures for several years and can also structurize them.
First trial rewards promote 1-trial learning and prolonged memory in pigeon and baboon. Proceedings of the National Academy of Sciences, 106(23), 9530-9533. One main theoretical result comes from Fagot and Cook who examined the capability of 2 pigeons to remember "picture–response associations" in one trial compared to 2 baboons. The two researchers were especially looking at 1-trial learning problems, that required complicated tasks over a long period, compared to previous research that was more focused on easier tasks over a shorter period. They also examined how these animals were forgetting these one-trial associations.
The researchers came across very striking results. They found out, that pigeons can remember "between 800 and 1,200 picture[s] [...]" and respond to them. Less than baboons that "[...] memorized 3,500–5,000 items and had not reached their limit [...]". They therefore conclude, that evolution has gradually increased the capability of long-term memory in animal brains. What they also discovered was, that pigeons as well as baboons were more likely to learn in one trial if they got a positive response for their first, initial try out. Surprisingly, they saw, that this first positive response had an effect for a very long time - “6 months in the pigeons and 8 months in the baboons” (Cook & Fagot, 2009). They associate these long lasting benefits to the “visual wulst” in pigeons.
According to Fagot and Cook, these results are associated to several human capabilities and traits: 1. the ability to judge persons only after a few minutes, 2. the huge impact of first impressions and 3. the growth of word knowledge during evolution. In the research of Kalenscher et al., pigeons were trained to decide and therefore to peck between smaller rewards that are given directly after pecking or bigger rewards that are given after a slightly longer time. During the experiment, the time (in the delayed reward category) was increased with every round. Through this experiment the researcher try to get a better comprehension of impulsiveness.
The results were that pigeons prefer short term rewards that are smaller over greater long term rewards, where the time difference between pecking and rewarding is increasing from time to time. During this experiments, Kalenscher et al. also observed the neuron activity and tried to relate them to the animals reward choice. The researcher found a constant activity if they looked at the neurons during the constant reward amount.
On the other hand, neural activity decreased if the delay was increased even though the reward amount increased. Therefore we can say, that the neuron activity is altered by the size of delay. According to Kalenscher et al, one can draw coherence with human behaviour patterns "such as drug addiction, pathological gambling, frontal lobe syndrome, and attention-deficit disorders, which are characterized by inappropriate temporal discounting and increased impulsiveness" (Kalenscher et al., 2005).
Downsides of pigeons
Pigeons have a smaller visual memory than e.g. baboons. Therefore, very complex experiments cannot be done. They can memorize around "830 [...] picture[s]" (Cook et al., 2012). Experiments that are used to examine cognitive skills and compare them to human's cognitive characteristics could be inexact, because a pigeon's memory is less developed than a human's memory. Pigeons are also not capable of performing higher cognitive tasks, because they do not have a cerebral cortex (Cook et al., 2012).
This makes it impossible to reflect results of pigeons directly on humans. Therefore it can be concluded that pigeons cannot compete with humans and baboons in terms of cognitive skills. However a great benefit of using pigeons is the fact that researchers have to take less ethical regulations into account and this therefore allows them to use pigeons more widely. On the other side, baboons and humans may be a better fit if the cognitive experiments are allowed on them (in terms of ethics) and a bigger cognitive capacity is required.