We may not think of childhood as a particularly stressful time in our lives, but growing up is scary. There are rules, actions and consequences that all young things must learn fast in order to survive. These early experiences can play a huge role in shaping individual behaviour and fitness in later life. So how should juvenile animals deal with stress during their development? Researchers at St Andrews and Oxford University, UK, say it's easy: just make friends.
Neeltje Boogert and her colleagues were interested in the developmental factors that drive individuals to become more or less social later in life. They suspected that stress, which young wild animals typically experience during periods of food shortage or sibling rivalry, plays a role in how individuals grow and develop into social adults. They tested their theory using a captive population of zebra finches (Taeniopygia guttata) in which they experimentally increased exposure to the avian glucocorticoid stress hormone, corticosterone. When the experimental chicks were 12 days old, half were fed a diet of peanut oil and half were fed peanut oil laced with corticosterone over the next 16 days. Boogert and her team then fitted the chicks and their parents with passive integrated transponder (PIT) tags to record their movement and interactions around experimental feeders in two free-flying aviaries over a 5 week period. The individual barcodes associated with the PIT tags recorded data on who was foraging with whom, which birds stayed close to their parents and which birds had more foraging partners. In essence, Boogert could see whether the stress hormone treatment predicted which individuals developed into the ‘social butterflies’ of the bird flock.
The group initially expected the corticosterone-treated chicks to be less social than their untreated siblings, based on some earlier research in great tits (Parus major). However, the zebra finches appeared to take stress in their stride, and responded to early-life corticosterone exposure by becoming more independent from their parents and spending more time with a wider variety of individuals compared with controls. Social network analysis also showed that stress-treated birds occupy more central positions in the network: in other words, they are more gregarious than their less social untreated siblings. The downside of this social flair is the strength of the friendships. The stress-treated birds formed weaker associations than the untreated birds as they tended to form fewer tight-knit associations.
Does having an outgoing social life help or harm birds in the long run? More research is needed to answer this question. If stress encourages independence in young birds, this may facilitate their dispersal away from poor habitats in the wild. However, fewer, but more stable friends may be better than many flaky ones when the going gets tough. In any case, these results make me reflect back on the times I was bullied as a kid…perhaps I have more friends today because of it!
