An individual's personality can have a big effect on their life. Some people are outgoing and gregarious while others find novel situations stressful, and animals are no different. ‘Over the last 5 years there has been increasing interest in animal personality,’ says Kathryn Arnold from the University of York, UK. Knowing that stress affects wellbeing by raising metabolism and increasing the levels of damaging reactive oxygen metabolites, Arnold and her colleagues wondered whether animal personalities could be reflected in their oxidative stress profiles (). Teaming up with graduate student Katherine Herborn at the University of Glasgow, UK, Arnold set about classifying the personalities of 22 greenfinches at Glasgow University's aviary.
First, the duo tested the bird's reactions to a novel situation. Adding a brightly coloured biscuit cutter to each greenfinch's food bowl, Arnold and Herborn timed how long it took for the birds to pluck up the courage to approach their lunches. ‘They wanted the food but they had to overcome their fear,’ explains Arnold. Repeating the experiments with different coloured biscuit cutters, the team found that the boldest birds took only a few seconds to overcome their fear while more timid birds took up to half an hour to approach their meal.
Having established each bird's courage, Arnold and Herborn measured the greenfinches' motivation to explore by attaching an intriguing object to the birds' perches. Timing how long it took the birds to land next to the object, the duo found that some birds were avid explorers while others were less curious. However, there was no correlation between the birds' courage and curiosity: some bold birds were unenthusiastic explorers while other shy individuals were very keen to investigate, so would their blood profiles reflect any of their behaviour traits?
Collecting blood samples from the birds several weeks after classifying their personalities, Herborn and Stephen Larcombe measured the animals' damaging reactive oxygen metabolite levels and their defences against these harmful molecules. Herborn also travelled to the WALTHAM® Centre for Pet Nutrition, UK, to measure the amount of oxidative damage sustained by each individual with the help of Lucille Alexander and Jo Coffey.
Comparing the bird's blood oxidative profiles with their personalities, the team found that the most timid birds had the highest levels of damaging oxygen toxins and the weakest defences, so they suffered more oxidative stress than braver individuals. Also, the scientists found that the most curious birds (which approached objects fastest) had better defences than less curious greenfinches, although there was no relationship between the birds' curiosity levels and their toxic oxygen metabolite levels. However, when the team analysed the degree of oxidative damage sustained by cells in the birds' blood, they were surprised to find that the intermediate birds suffered the most damage while the most timid and the boldest birds had much lower damage levels. So the individuals that reacted strongly to novel objects – whether they approached immediately or held back – had lower oxidative damage levels than individuals that reacted calmly.
Having found that the birds' personalities are reflected in their oxidative stress profiles, Arnold is keen to find out how this may impact on birds in the wild. She says, ‘Neophobic birds [which are afraid of new things] may suffer high costs of oxidative stress but they might be less likely to be eaten by a predator because they are more wary; however, these individuals may die early because they paid these physiological costs.’
