Tomorrow, 8 October, is World Migratory Bird Day, an international awareness day as birds embark on their seasonal migration. These epic journeys happen twice a year, one for each migratory season. 

Tītī/ sooty shearwaters, toanui / flesh-footed shearwaters, and many other seabirds return to our shores in spring from their winter grounds in the distant seas of Japan, Alaska, California, and South America.

On these journeys, they face many threats, including from fisheries bycatch, plastic pollution, and changing prey distributions due to warming ocean temperatures.

One threat that is not yet well-understood is light pollution at sea. Vessels such as fishing boats, container ships, and cruise ships may all have bright outside lighting that attracts and disorients birds, leading to ‘vessel strikes’ (collisions with ships) and subsequent drownings.

“The vastness of the open ocean means that it’s very difficult to understand this threat at sea,” says Johannes Fischer, DOC Technical Advisor. “Most of our knowledge comes from terrestrial studies.”

To understand light pollution impacts at sea better, researchers at DOC recently attached light-sensitive tracking tags to 179 seabirds across seven different species. These tags record light exposure events and exactly where they occur.

Graeme Taylor, Principal Science Advisor at DOC, has been putting light-sensitive tags on seabirds since 2005, but this new research has vastly expanded our understanding of which species are most threatened by light pollution at sea.

“We were seeing these light “events” during the dead of night,” says Graeme. “At first, we thought they might be lighthouses, but this new research shows these events happening out over the deep ocean where there isn’t any land.

"We’ve concluded the light must be coming from ships.”

The good news is that some of our most endangered seabirds, such as the Chatham Island tāiko, kuaka/Whenua Hou diving petrel, and ranguru/Chatham petrel, seem to encounter relatively little light pollution out at sea.

However, more than a third of tītī Wainui/fairy prions, toanui/flesh-footed shearwaters, and tītī/sooty shearwaters encountered light pollution throughout the Pacific, particularly between Japan and Hawaii, Alaska, and southeast of Aotearoa.

“We can work with vessel owners to reduce this risk,” says Johannes Fischer. “Minimizing light use around seabird colonies, shielding lights, and changing bulbs are some of many actions that can reduce vessel strikes.”

Minimizing light pollution doesn’t just benefit birds, however. It has impacts on nearly all ecosystem levels, from other large migratory species, the fish and squid that seabirds snack on, to the plankton that migrate to the sea surface at night.

“Our seabirds connect the oceans and connect Aotearoa to the rest of the world. It’s our job to protect them on their spectacular migrations.”

Read the research: Estimating seabird populations to offshore light pollution.

All tracking results have been made open access by DOC through an online tool: Seabird Night Time Light Exposure tool (external site).