The plan is now to conduct experiments to check if the colour preference goes beyond food, say scientists.
Credit: Sourabh Biswas
New Delhi: Indian stray dogs have a very strong preference for yellow colour and their liking is so strong that they even ignore tasty biscuits or chicken pieces in favour of empty yellow coloured bowls, biologists have shown.
In a unique study involving 134 stray dogs, scientists at the Indian Institute of Science, Education and Research, Kolkata have demonstrated such a strong colour preference in canines overcoming even the appeal of food.
The plan is now to conduct experiments to check if the colour preference goes beyond food. “For instance, will a person sporting a yellow tee shirt attract more attention from street dogs than someone wearing black? We want to check,” IISER scientist Anindita Bhadra, who led the 11-member team, told DH.
For over three decades, scientists knew dogs are dichromatic – they can see only yellow and blue, apart from the greyscale (black, white and grey). In comparison, humans can see three colours: red, green and blue.
To check how the free-ranging dogs respond to colours, the researchers carried out field experiments in which they fanned out in the streets in Nadia, North 24 Parganas and Kolkata districts. On encountering a stray dog one of the researchers would place the bowls, attract the animals towards the experimental set-up and watch the response.
In one test involving 76 dogs, as many as 46 went to the yellow bowl with biscuits whereas 18 picked up the food from the grey bowl and 16 from the blue one. When bowls are empty, 30 out of 58 dogs explored the yellow ones, while 14 each chose grey and blue.
Subsequently, the researchers experimented with empty yellow bowls and grey/blue bowls with food.
In the case of biscuits, 41 of 52 dogs preferred empty yellow bowls and only 11 ate biscuits from grey bowls. Similar trend was visible with chicken as 47 out of 61 stray dogs preferred empty yellow bowls ignoring grey bowls with chicken. This is even when the dogs can see and smell the chicken.
The results – published in Animal Cognition – surprised the researchers who are continuing the experiments with plastic balls and commercial carry bags to see how far the colour preference of the dogs can go. They also plan a test with differently coloured clothes.
“Our experiments demonstrate a clear preference for the colour yellow over blue and grey in free ranging dogs of India, at least in the context of foraging. This preference is so strong that it supersedes their attraction towards food, whether biscuit or chicken. This is the first time that we have observed dogs ignore a clear food reward in a choice test,” the team reported in the journal.
Will the pet dogs show similar colour preference? A few recent experiments came up with suggestions that pets too may have a similar preference, but not as strong as the Indian stray dogs.
“While domestication often dilutes the preferences in dogs, it is also possible that our strays have been taking a cue from the environment as most of the Indian food (leftover thrown in the dumps frequented by the strays) are yellow in colour to the dogs’ eyes because of the turmeric and red chilli,” Bhadra said.
“Further experiments can help us understand the ecological advantages, if any, of this preference and the reasons behind it,” she added.