Friends warn friends about feasts and famines

Many years ago, Eleanor Roosevelt famously quipped, ‘Learn from the mistakes of others. You can't live long enough to make them all yourself’. Little did Eleanor know that her words would not only apply to human behaviour but also to the physiology of a highly social songbird. The red crossbill (Loxia curvirostra) is a nomadic species whose flocks travel far and wide in search of foraging grounds abundant with conifer seeds. As seed production can be unpredictable from year to year, red crossbills are often challenged by periods of food deprivation that can have devastating impacts on their body condition. In her recent study, Jamie Cornelius from Ohio State University, USA, shows that red crossbills can learn from the mistakes of their food-deprived friends, inducing coping mechanisms that prepare them for challenging food conditions ahead.Animals can gather information about the environment through their own experiences, but may also glean information by observing others. Thus, Cornelius questioned whether red crossbills that observe the deterioration of their underfed friends would make behavioural and physiological adjustments to prevent themselves from meeting that same fate. She tested this idea by housing pairs of birds in side-by-side cages. One bird in each pair was selected to be a well-fed onlooker, keeping an eye on its adjacent neighbour for 3 days, while the neighbour was placed on a strict diet and only permitted to eat during two short feeding windows per day. Following the 3 day experience, Cornelius then restricted the diet of the well-fed onlooker to determine whether observing their famished neighbour's predicament had changed how they responded to food scarcity.Cornelius discovered that when the onlooker birds were placed on meagre rations, they lost less weight. They ate more during the brief windows when food was available, as though their neighbour had warned them to ‘eat what you can, when you can’. In addition to this behavioural change, Cornelius also found physiological changes. Warned of a dwindling food supply, the onlooker birds kept their flight muscles in tip-top shape, which is important when food conditions are so grave that birds must fly long distances in search of better dining opportunities. The onlooker birds also had larger intestines, which Cornelius thinks improves how efficiently food is digested and ultimately helps to reduce their weight loss during periods of famine.As with any good study, Cornelius's findings left her with many more questions. She learned that knowledge gained by observing others in their surroundings can alter bird behaviour and physiology, but how these changes are mediated remains a mystery. Luckily, she has a hunch. Her previous work demonstrated that red crossbills that are forewarned of poor environmental food conditions by their friends mount a large stress response when food is scarce. The stress response involves elevating levels of the stress hormone corticosterone, which is thought to enhance survival in birds during periods of environmental stress by increasing foraging behaviour. Thus, corticosterone may act as a messenger between the brain and the rest of the body, helping to mediate between behaviour and physiology.For red crossbills, it seems that Eleanor Roosevelt's edict to ‘learn from the mistakes of others’ could be a matter of life and death. If birds don't learn from the misfortunes of others, they may not survive long enough to make the same mistakes themselves. Fortunately, the hardships endured by some in the flock could caution others to avoid meeting the same fate.

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