Birds vary in response to stress

A NOTABLE centenary passed almost unnoticed this autumn; in August 1914, the Endurance set sail for Antarctica. 

The three-masted barque became trapped in the ice of the Weddell Sea, was crushed to pieces and sank, leaving 28 men stranded with no hope of rescue. Their leader, however, was an extraordinary Irishman, Ernest Shackleton. Thanks to his bravery and judgement nobody was lost.

The great explorer’s 1,267km journey, with five companions in a six-metre open boat, from Elephant Island to South Georgia is legendary. The Titanic had fallen victim to ice two years previously but its captain, Edward Smith, was no Shackleton. Overcome by the enormity of the looming disaster, he sank into emotional paralysis. Had he taken charge of the situation, all of the ship’s lifeboats might have been launched filled to capacity and many more lives saved.

Wild creatures, too, must deal with the unexpected. Are there the equivalents of Shackleton and Smith among them or do all individuals cope equally well with the unexpected? Trying to answer this question, John Cockrem of New Zealand’s Massey University has been examining the responses of little, or ‘fairy’, penguins to stress. The ones breeding near Oamaru, on New Zealand’s South Island, have been well studied and ‘personality profiles’ developed for many of them. Cockrem’s findings to date were presented at a meeting of the American Physiological Society in San Diego this month.

The fairy, about half a metre tall, is the smallest of the world’s 17 penguin species. It breeds colonially on the southern coasts of Australia and New Zealand. Visitors to Melbourne will know the bird. The famous ‘penguin parade’ takes place nightly on Phillip Island, 137km south of the city. The birds assemble offshore in the late evening. Then, a few minutes after sunset, they waddle up the beach, like parading soldiers, to their nesting burrows, watched by crowds of people sitting on benches. They are, apparently, Australia’s second most popular tourist attraction. Having been to Phillip Island and seen the marchers pass almost within touching distance, taking no notice of the audience, the laid-back little penguin seemed to me an unlikely candidate for a study of stress.

Being captured is scary for all birds but there is considerable variation in responses between species. Bluetits, caught for ringing, will fight back, biting fingers and drawing blood on occasion. They appear angry rather then frightened. Bullfinches, on the other hand, don’t struggle at all. Like the unfortunate Captain Smith, they seem unable to respond to the situation. ‘Highly-strung’, they must be cosseted and handled gently. There are variations too between individuals of the same species. Some appear unfazed by the experience of being captured while others seem deeply outraged. David Lack in The Life of the Robin described cases of ‘trap addiction’; birds entering his traps repeatedly, even when no bait was placed in them. These attention-seekers seemed to enjoy being handled. I have known birds to sing while being ringed.

Mammals, including humans, release cortisol into the bloodstream when stressed. Birds secrete corticosterone. These hormones stimulate the adrenal gland, triggering responses to a perceived threat. Cockrem measured corticosterone levels in little penguins under stress. He hopes to relate the readings obtained to the birds’ individual dispositions. Breeding success and productivity, he expects, will be affected by sensitivity to stress.

When captured, some of the penguins released up to 15 times more corticosterone than others. Those with low responses, Cockrem argues, have a business-as-usual approach to change. Birds with a high corticosterone response have more ‘reactive’ personalities; they won’t sit and do nothing when confronted by the shock of the new. Climate change, according to the some estimates, is directly affecting about half of all bird species. If Cockrem is right, the Shackletons of the bird world should fare better than the Captain Smiths in the trials and tribulations ahead. Are we seeing a natural selection of personality types among our birds?


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