By Jody Bourton
Earth News reporter
A bird's eye view of another flying albatross and killer whale (indicated)
Albatrosses associate with killer whales out in the open ocean, tiny cameras attached to the birds reveal.
Unique pictures retrieved from the cameras placed on the albatrosses' backs show the birds feeding alongside the killer whales, also known as orcas.
The birds are thought to feed on food scraps left by the marine mammals.
The discovery may explain how black-browed albatrosses find their prey in an apparently featureless open ocean, say the researchers.
Black-browed albatrosses (Thalassarche melanophrys) travel hundreds of kilometres to locate and feed on their prey.
They may travel large distances in only a matter of days to feed on fish before returning to their breeding colony on Bird Island, South Georgia in the southern Atlantic Ocean.
Although a number of studies have looked at the foraging behaviour of albatrosses, it is not known exactly what strategy the birds employ to locate food on the open sea.
Bird's eye view
Now scientists report in the journal PLoS ONE that miniaturised cameras attached to the back of the birds have revealed the birds fly in groups and forage with killer whales.
"We went through thousands of images manually, we were so bored because most of images showed just 'featureless' ocean," says Professor Akinori Takahashi from the National Institute of Polar Research, Tokyo, Japan.
"Then we suddenly saw some albatrosses flying in front of the camera bird and then found the killer whale in the image."
"Finding the interaction of albatrosses with killer whales in the open ocean is unique, because it provides a clue to explain [how] some fish species unavailable within a diving range of albatrosses often appeared in their diet," he explains.
Prof Takahashi undertook the study with colleagues from Hokkaido University in Sapporo, Japan and the British Antarctic Survey, Cambridge, UK.
Secret associations, the black-browed albatross
By following killer whales, the scientists believe the birds benefit from the mammal's own foraging and hunting behaviour.
"Albatrosses can not dive deep, and prey remains from killer whales or the fish driven to the surface by whales would be good source of food," Prof Takahashi suggests.
The scientists believe this event is not a one off, and that it may be a specific feeding strategy for the large ocean-going birds.
"Previous dietary studies showed black-browed albatrosses often feed on fish species unavailable within their diving capacity, 5 or 10m from the sea surface," Prof Takahashi says.
"Researchers are not sure how albatrosses got these fish, and assume they got them from the interactions with commercial fisheries."
"Our study suggests that these fish are available to albatrosses, in part, through interaction with deep-diving marine mammals."
The albatrosses may also save energy by scavenging on stationary prey items left by killer whales rather than pursuing live prey on the surface or by plunging into the sea, the researchers suggest.
In January 2009, the team captured four birds at the nesting sites on Bird Island and attached a specially developed stills camera system to each using waterproof tape.
An iceberg photographed from the back of an albatross
Each camera, placed in the centre of the bird's back, weighed just 83 grams, and was able to take up 10,000 images during the bird's flight.
Taking a picture every 30 seconds, it also recorded environmental data.
The team released the birds and waited for them to come back from their foraging trips.
"After two to four days when the birds returned the colony, we recaptured them and the data loggers were retrieved. The data loggers archived image, depth and temperature data," Prof Takahashi says.
The team were then able to download the information and images from the retrieved camera system.
Bird and whale
Scientists have previously noted associations between albatrosses and killer whales but these mostly took place in shallow water.
Prof Takahashi's team now hopes to use even smaller cameras to find out more about the albatrosses' behaviour.
"We hope to develop a camera lens unit that can be attached on the head of albatrosses in the future. But this is an important first step," Prof Takahashi says.
"I think we now have good understanding of where the birds go, thanks to recently developed sophisticated tracking methods."
"But we still need to learn more about what the birds are actually doing in the open ocean."