Scientists have captured unique on-board footage of Indian Ocean seabirds speeding just above the waves to catch flying fish on the wing.
The footage, obtained by lightweight bird-borne cameras formed part of a study of the lives of seabirds in the waters around the remote archipelago they call home.
Two red-footed boobies - a tropical cousin of the more familiar gannet – were carefully fitted with the tiny cameras to record how they catch their favourite food; flying fish. Of 15 capture attempts, 14 were towards flying fish while in flight and one was an underwater dive.
This is the first such on-board footage revealing that flying fish are caught on the wing.
"The cameras recorded footage of the birds catching flying fish just above the surface of the water, while on the wing," said Dr Ruth Dunn, a Visiting Researcher at Lancaster University and lead author of the study. "We suspected this happened, but this is the first time that we've had bird-borne footage like this showing them foraging and catching fish mid-air. It could suggest they are catching a significant portion of their diet in this way."
In addition, the research team used small GPS and accelerator tracking devices on 18 more red-footed boobies in the remote Indian Ocean archipelago to show how they use the wind to travel hundreds of kilometres over the deep blue open ocean to hunt fish.
Red-footed boobies have long narrow wings relative to their bodies enabling them to glide quickly and efficiently in high crosswinds. The study showed they prefer tailwinds and crosswinds, especially on their outward journeys towards their feeding areas.
Red-footed boobies hunt in the open ocean and do not stick to specific feeding sites because their prey can be patchy and moves around. The researchers show the birds' selection of favourable winds allows them to conserve energy while travelling and searching for food.
By selecting favourable winds, the birds reached higher speeds without needing to increase flapping. The researchers believe that the birds may have adapted this behaviour to the unpredictable, patchy food options available to them.
The trackers showed that the birds were more likely to continue to hunt in windier conditions and less likely to rest. This is possibly because when it is windier the flying fish stay in the air for longer which provides better opportunities for the birds to catch them.
"We found that the birds foraged in windy conditions and we think that this might be because flying fish are able to glide in the air for longer in these conditions, making them more accessible to the boobies," said Dr Dunn.
Understanding how the behaviour of birds, and other flying species, are influenced by winds is of growing importance at a time when global airflow patterns and intensities are shifting due to climate change.
The red-footed booby findings contrast to those by other researchers studying some albatross species, which find it harder to catch prey in windier conditions.
The researchers believe their findings will help provide a clearer picture of how red-footed boobies will fare in a changing world.
"This is the first step in helping us to understand more about how wind influences the behaviour and distribution of tropical seabirds," said co-author Professor Stephen Votier, from The Lyell Centre, Heriot-Watt University's global institute for Earth and marine sciences. "By gaining a clearer understanding of such environmental effects will enable us to predict how they will cope in the future."
The study, which was supported by the Bertarelli Foundation, involved researchers from Lancaster University, Heriot-Watt University, the University of Exeter, and ZSL.
Their findings are outlined in the paper 'Commuting in crosswinds and foraging in fast winds: the foraging ecology of a flying fish specialist' which is published in Proceedings of the Royal Society B.
