My diving is terrible – I can never clear my ears properly, even within 1 m of the surface – which makes the achievements of diving Atlantic puffins even more impressive, plummeting 150 m down with no apparent concern for their ears. ‘It is conceivable that the air-filled sinuses and auditory abilities are modified in auks, perhaps to withstand deep dives or enable underwater hearing’, says Aran Mooney, from the Woods Hole Oceanographic Institution, USA. Yet, it wasn't clear how the puffins’ amphibious lifestyle might impact their hearing out of water and whether they are distressed by noise. Mooney explains that other species are clearly disturbed by human noise, spending less time on the nest when people are around. Joining Ole Larsen and Kirstin Hansen, from the University of Southern Denmark, and Marianne Rasmussen, from the University of Iceland, Mooney and Adam Smith travelled to northern Iceland to collect puffins as they emerged from their burrows, to test their hearing.
‘The burrows are often on high cliffs, so are a bit perilous to approach and work near, given the sheer drop and potential instability’, says Mooney, who eventually captured nine birds. After transporting them to an improvised lab in a nearby farm shed, the team gently sedated the animals and inserted fine electrodes beneath their skin before recording their responses to clicks ranging from low-pitched 125 Hz tones to 8 kHz beeps at a 20 dB whisper up to 100 dB to find out which frequencies the puffins were most sensitive to. Although the birds could hear sounds up to 6 kHz, their hearing was sharpest between 750 Hz and 3 kHz. And, when the team compared the birds’ hearing with that of other similarly sized birds, it seemed that their aquatic lifestyle has not affected their hearing at all: it's just as good as that of birds that never plunge beneath the waves. However, the team suspects that the windswept locations of the birds’ nesting sites with the noise of waves crashing below could limit their hearing above ground.
The hearing of these charismatic birds is probably fine-tuned to the cries of their own chicks and other puffins. In addition, they are also less likely to be disturbed by their noisy surroundings when secluded in their burrows. However, Mooney believes that the thud of approaching human feet is likely to penetrate their otherwise peaceful homes. ‘Given the influence of human encroachment on bird colonies, the sensitive hearing of these animals and the fact that puffins are a major tourist attraction in many countries, we suggest that human disturbance noise, even low-level sounds from hikers and visitors, has the potential to disturb puffins’, he says.