Muttonbirds pursue endless summer across Pacific

It's an epic journey for a small bird. A team of scientists from New Zealand, the US, and France has discovered that sooty shearwaters (known to Kiwis as muttonbirds or titi) make a 64 000 km round trip each year, chasing summer across the Pacific.

8 August 2006

Migration pathways of two tagged muttonbirds, overwintering off California and Japan. (Credit: Courtesy of Scott Shaffer, University of California)

'This is the longest animal migration recorded via an electronic tracking device', says Paul Sagar, a seabird biologist at NIWA, who took part in the study. The results will be published online in the prestigious American journal Proceedings of the National Academy of Sciences in the week beginning 7 August.

Sooty shearwaters are one of the most abundant seabirds in the world, but populations are declining. Following their movements could help shed light on the causes of this decline, thought to be linked to climate change and entanglement in fishing gear. But tracking a bird that spends 90% of its time at sea isn't easy.

Recent developments in technology are now enabling scientists to track birds as small as sooty shearwaters, which are about the size of a small seagull. For this study, the team used small light-sensitive electronic tags to follow the migration of 19 sooty shearwaters from breeding colonies on Whenua Hou (Codfish Island) and Mana Island, New Zealand. The tags used light and temperature levels to record each bird’s location every day over a migration period lasting several months.

All the tagged birds followed a figure-of-eight pattern across the Pacific, crossing between southern and northern hemispheres in pursuit of an endless summer. Each bird covered an average of about 64 000 km in 200 days, covering distances of up to 910 km per day.

Scientists previously thought that the birds spent the northern summer roaming around the north Pacific. This study revealed that, instead, the birds remain in one of three areas – off Japan, Alaska, or California. This finding has implications for muttonbird conservation, as levels of fishing and ocean productivity are different in these three areas.

'This extraordinary migration probably allows muttonbirds to feed in nutrient-rich waters throughout the Pacific', says Mr Sagar. Because they range so widely, and are at the top of the food chain, muttonbirds may make good indicators of climate change and ocean health.

'Rakiura Maori are excited with the results of this research into their Taonga', says Tane Davis, chairman of the Rakiura Titi Island Administrating Body, who supported this study. This type of collaborative research supports one of the many objectives of the Kia Mau Te Titi Mo Ake Tonu Atu research project.

For more information on this study, please contact:

Mr Paul Sagar
NIWA Science

Dr Scott Shaffer
University of California, Santa Cruz, US
Tel: +1-831-459 1291 (from 07/08/06)
Mob: +1-408-761 8201 (from 03/-8/06)
[email protected]

Associate Professor Henrik Moller
Centre for Study of Agriculture, Food & Environment (www.csafe.org.nz)
University of Otago
Tel: +64-3-479 5327
Mob: 027 2268688
[email protected]

For information on Kia Mau Te Titi Mo Ake Tonu Atu research project, contact :

Mr Tane Davis,
Chairperson, Rakiura Titi Islands Administering Body.
Tel: +64-3-2130788
Mob: 027-438 0366
[email protected]

Background Information

1. The sooty shearwater (Puffinus griseus) is a species of small seabird (weighing 800 g) that ranges across all the world’s oceans, but breeds only in temperate and subantarctic regions of the Southern Hemisphere. The main breeding colonies in New Zealand are on the islands off Stewart Island, the Snares, and Auckland, Chatham, Antipodes and Campbell Islands. Females lay a single egg in a burrow in late November or early December. The sight of hundreds of thousands of sooty shearwaters returning to their burrows at night is one of nature’s most striking spectacles. The birds feed on small fish, squid, and crustaceans, diving up to 70 m to catch their prey or scavenging behind fishing boats.
2. Sooty shearwaters are the most common 'muttonbird' in New Zealand, with chicks harvested for food each year. The harvest of titi from islands adjacent to Rakiura (Stewart Island) is one of the few remaining native wildlife harvests managed entirely by Maori. This work is of particular significance to the Rakiura Maori, who harvest titi and are the kaitiaki (guardians) of the birds, as little was known about the movements of the birds once they left their breeding islands. This research will therefore provide conservation benefits at sea and at breeding colonies.
3. Scientists from NIWA, the University of Otago’s Kia Mau Te Titi Mo Ake Tonu Atu research team, the University of California at Santa Cruz, and the New Zealand Department of Conservation tagged shearwaters at breeding colonies on Whenua Hou (Codfish island), off Stewart Island in New Zealand’s deep south, and Mana Island, off the Wellington coast, during the period January to March 2005.
4. 'Geolocator' tags weighing about 10 g were strapped to the birds' legs. These are a new generation of small electronic data loggers which record diving depth and environmental temperature as well as longitude and latitude, making it possible to track the birds' movements across the globe. The information on latitude and longitude can be stored in the tag for up to two years, and is retrieved by recapturing the birds when they return to their breeding colonies and removing the tags. In this study, information was retrieved from 19 birds between October 2005 and February 2006.
5. The birds began their epic journey in southern breeding grounds in late April to early May, heading first east, then northwest to reach one of three wintering grounds in the North Pacific (off Japan, Alaska, or California) by late May. Some of the birds visited the coast of Chile before heading northwest, a pattern not observed before. Come October, they made the return journey, heading southwest to their New Zealand breeding grounds. As they did so, their passage over the equator was remarkably synchronized, with all the birds passing through a narrow corridor within a period of only five days.
6. The birds also foraged in southern locations as far south as 65 degrees South during the breeding season, diving to depths of 70 m and experiencing ocean temperatures ranging from near freezing to as high as 29 degrees Celsius as they flew from the Antarctic polar front then northward across tropical waters to subarctic waters.
7. Sooty shearwaters stay at sea during the migration. They are not known to contract the potentially deadly H5N1 strain of bird flu and are unlikely to mix with any birds known to contract this virus.
8. This study was led by Dr Scott Shaffer of the University of California, Santa Cruz, with funding from the National Science Foundation, NIWA, FRST (NZ), the Gordon and Betty Moore Foundation, and the David and Lucile Packard Foundation. The New Zealand Department of Conservation and the Whenua Hou Management Committee granted access to the breeding colonies. This study contributed to the joint research by the Rakiura Titi Islands Administering Body and the University of Otago’s Kia Mau Te Titi Mo Ake Tonu Atu research team into the sustainability of the muttonbird harvest. More information about the Kia Mau Te Titi Mo Ake Tonu Atu research project can be found at www.otago.ac.nz/titi/default.html