A new study into how shearwaters navigate at sea has shown that olfactory information is a key requirement.
The research, published in the journal Scientific Reports, looked into how birds navigate over long distances at sea and closer to the shore. Researchers monitored 32 Scopoli’s Shearwaters off the coast of Menorca.
The birds were split into three groups. One had the sense of smell removed using zinc sulphate; a second was subject to magnetic disruption with neodymium magnets; a control group had a normal sense of smell. The birds’ movements as they travelled to distant foraging grounds for food were then tracked using GPS loggers.
It was found that all three groups successfully navigated to the foraging grounds and found food. However, on the return journey the at-sea anosmic birds – those with an impaired sense of smell – showed significantly different orientation behaviour from the other two groups. Instead of being well-orientated towards home when they were out of sight of land, the birds embarked on straight but poorly oriented flights across the ocean.
Their orientation improved when approaching land, suggesting that the birds consult an olfactory map when out of sight of land, but are subsequently able to find their way using familiar landscape features.
The study concludes that there is good evidence that the effect on homing orientation was caused by a lack of olfactory information.
Scopoli's Shearwater (Natalino Fenech).
Study leader Oliver Padget commented: “Navigation over the ocean is probably the extreme challenge for birds, given the long distances covered, the changing environment, and the lack of stable landmarks. Previous experiments have focused on the physical displacement of birds, combined with some form of sensory manipulation such as magnetic or olfactory deprivation. Evidence from these experiments has suggested that removing a bird’s sense of smell impairs homing, whereas disruption of the magnetic sense has yielded inconclusive results.
“However, critics have questioned whether birds would behave in the same way had they not been artificially displaced, as well as arguing that rather than affecting a bird’s ability to navigate, sensory deprivation may in fact impair a related function, such as its motivation to return home or its ability to forage.
“Our new study eliminates these objections, meaning it will be very difficult in future to argue that olfaction is not involved in long-distance oceanic navigation in birds.”
Padget O, Dell’Ariccia G, Gagliardo A, González-Solís J & Guilford T. 2017. Anosmia impairs homing orientation but not foraging behaviour in free-ranging shearwaters. Scientific Reports, doi:10.1038/s41598-017-09738-5.