Olfaction (sense of smell) is a key factor in long-distance oceanic navigation in birds, according to a new University of Oxford-led study.
Cory’s shearwaters from the Crossley ID Guide Britain and Ireland. Image credit: Richard Crossley / CC BY-SA 3.0.
“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,” said study lead author Oliver Padget, a DPhil student in the Animal Behaviour Research Group in the Department of Zoology at the University of Oxford, UK.
“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.”
In the study, Padget and his colleagues from the Universities of Oxford, Barcelona and Pisa followed the movements and behavior of 32 free-ranging Scopoli’s shearwaters (Calonectris diomedea) off the coast of Menorca, Spain.
The birds were split into three groups: one made temporarily anosmic (unable to smell) through nasal irrigation with zinc sulphate; another carrying small magnets; and a control group.
Miniature GPS loggers were attached to the birds as they nested and incubated eggs in crevices and caves on the rocky Menorcan coast. But rather than being displaced, they were then tracked as they engaged in natural foraging trips.
All birds went out on foraging trips as normal, gained weight through successful foraging, and returned to exchange incubation periods with their partners.
Thus, removing a bird’s sense of smell does not appear to impair either its motivation to return home or its ability to forage effectively.
However, although the anosmic birds made successful trips to the Catalan coast and other distant foraging grounds, they showed significantly different orientation behavior from the controls during the at-sea stage of their return journeys.
Instead of being well-oriented towards home when they were out of sight of land, they embarked on curiously straight but poorly oriented flights across the ocean, as if following a compass bearing away from the foraging grounds without being able to update their position.
Their orientation then improved when approaching land, suggesting that birds must consult an olfactory map when out of sight of land but are subsequently able to find home using familiar landscape features.
“To the best of our knowledge, this is the first study that follows free-ranging foraging trips in sensorily manipulated birds,” said study senior author Professor Tim Guilford, also from the Department of Zoology at the University of Oxford.
“The displacement experiment has — rightly — been at the heart of bird navigation studies and has produced powerful findings on what birds are able to do in the absence of information collected on their outward journey.”
The findings were published August 29, 2017 in the journal Scientific Reports.
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O. Padget et al. 2017. Anosmia impairs homing orientation but not foraging behaviour in free-ranging shearwaters. Scientific Reports 7, article number: 9668; doi: 10.1038/s41598-017-09738-5
This article is based on text provided by the University of Oxford.
