The sunk cost effect in pigeon behaviour.

The sunk cost effect in pigeon behaviour.

Eva and Jason had just finished a long morning trading in stocks in Canary Wharf. Every day at lunch time they liked to like to get out of the grey, poorly lit office and eat their lunch outside in Jubilee Park. They always sat on the same patch of grass and watched the pigeons and people pass by. As they ate Eva noticed that one of the pigeons tended to stick to the same area of the park, pecking around and looking for food rather than move to another area of the park where more people were sat around enjoying their lunches. Eva mentioned the pigeon to Jason and they both wondered why the pigeon would not move to the area of the park with more food.

In humans when an individual is given the choice between two or more investment decisions people often stick with the investment they are already involved in rather than moving to a new investment (Novemsky & Kahneman, 2005). The initial investment of resources (money, time, energy etc) make switching investments less likely even if the new investment could produce a better outcome than the original investment – psychologists call this tendency to stick with the original investment the sunk cost effect (or bias) (Avila et al., 2010). One explanation of the sunk cost effect is that people have strong misgivings about wasting resources, a disposition that economists call loss aversion (Novemsky & Kahneman, 2005).

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Like humans, other animals (other than humans) often show the same decision behaviours. Several studies have investigated the sunk cost effect in pigeons (for a review see White & Magalhaes, 2015). In one study by Pattison and colleagues (2012) at the University of Kentucky researchers examined decision behaviour in pigeons (Columba livia). The pigeons were trained to peck at coloured keys with a potential reward (food). The pigeons could make a choice between pecking at one key for 30 pecks with a potential reward (e.g., a red key) or switching to another key (e.g., a green key) with a potential reward after 10 or 20 pecks. The pigeons showed a bias towards continuing with the sequence of pecks that they had invested in rather than switching to peck on another key that would produce a reward after fewer pecks. These results show that pigeons, like humans, show a bias to stay with an initial investment.

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A second study investigating decision behaviour in pigeons used a slightly different method to Pattison and colleagues (Watanabe, 2009). The pigeons in this study still had the same choice of sticking with an initial investment (in pecks) or switching. After training the pigeons to peck 30 times at one colour for food and 10 times to another colour for food Watanabe gave the pigeons the choice of switching to the 10-peck option after they had already started the 30-peck option. The experimenters found that three of the four pigeons showed a preference for completing the initial investment, despite the fact that switching to the second option would need pecks overall. So, like humans the pigeons in this second study were also susceptible to the sunk cost effect. Although these results are interesting the resources conceded that there may be one alternative explanation for the behaviour pigeons – switching to the new alternative would require the pigeon to move to the new colour.

Therefore, although most people would like to think that we do not act in the same way as other animals some of our behaviour is not uniquely human. Next time you find yourself sat on a patch of grass like Eva and Jason enjoying your lunch whilst watching the local wildlife and wondering why that pigeon is acting so strangely simple think “what would I be doing if I were that pigeon?” Afterall, the pigeon stubbornly sticking to its little patch of the park is not too unlike the way that our investment bankers and stock brokers behave.


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