Sea Birds

Sea Birds

Sea Birds

Environmental Indicators of the Oceanic Islands 

by David Hyrenbach & Guillermo Luna-Jorquera – Esmoi

Seabirds have always played a very important role in the mythology and culture of Polynesia. In Hawaii, for example, navigators used pikemen (kena), tropical birds (tavakes) and terns, especially the white tern, to find oceanic islands, because they knew that these birds did not stray far from the coast. The latter, the (Gygis alba or Manu-o-Kū), considered it as a major signal that they are approaching an island.

This little bird goes fishing in the morning and returns to its nests in the afternoon. Therefore, a sighting of one of these birds with a fish in its beak means that it is on its way back to its nest, where its hungry chick awaits (see photo 1). Following the same direction of the tern, the navigators arrived at small remote islands in the middle of the great Pacific Ocean. In short, seabirds provided valuable clues to mariners, which allowed them to anticipate and respond correctly to changes in the sea.

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Now that we are faced with some enormous environmental challenges, with the increase in plastic contamination in the seas, climate change and the depredation of fishery resources, the sea birds continue to be valuable indicators of the conditions and changes in the marine world and the oceanic islands

In Hawaii and Rapa Nui, scientists use birds as “biological sensors” of the marine environment, able to take samples while feeding on squid, fish and crustaceans and to store this information in their stomachs and tissues. The regurgitated birds (see photo 2) provide information about the plastics and the prey from which they feed. In addition, using small samples of blood and feathers, information is obtained on the trophic level (in which step of the food web they are), and on contamination with persistent organic compounds (such as DDT and DDE) and heavy metals (such as mercury and lead).

In this way, birds become living libraries, which collect environmental conditions at sea and in their prey. In particular, new analytical techniques, such as genetics and isotopes, are allowing the study of marine ecosystems through the diet of birds. Using samples of stomach contents and bird droppings, it is possible to determine the number and type of species in your diet.

In some cases, such as the frigate birds (makohe), the birds carry plastics to their breeding grounds to build their nests. This can be seen dramatically on Salas y Gomez Island where all the nests of the frigate birds that we were able to examine are made of plastic ropes (see photo 3). In other cases, such as that of the Midway albatross, the parents feed their chicks in the nesting colony with plastics, which are then regurgitated by the young before they leave the nest. However, other species, such as the petrels and the shearwaters, don’t vomit out the plastic that they ingest. Therefore, scientists collect the birds which died accidentally  (due to interaction with the fishing industry, to their attraction to street lights or ship lights or by attacks from stray dogs) to do autopsies. This permits us to study their stomach contents and tissues, in order to collect and quantify the rubbish to establish measurements on the quantity and type of plastic in the sea

For example, in a Polynesian Swallow found dead in Salas y Gomez we found 486 small pieces of plastics (see photo 4). This is very similar to what is observed in the Laysan albatross and black paw from the islands of Midway and Kure (Hawaii), where it has been documented that 100% of chicken regurgitations contain plastic (see photo 5) . These high incidences and quantities of plastics are only found in species that live near or within the great oceanic turns, where microplastics accumulate. In this way, these indices help to understand the geographical patterns of marine pollution and their tendency over time.

However, we still have several challenges that prevent us from applying these ideas throughout the Pacific Ocean. In many islands, for example, populations of seabirds have been decimated, and are relegated to small uninhabited islets. Therefore, these populations have to be rehabilitated and protected from the impacts of introduced predators, such as rats, cats and dogs.

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For example, in a Polynesian Swallow found dead in Salas y Gomez we found 486 small pieces of plastics (see photo 4). This is very similar to what is observed in the Laysan albatross and black paw from the islands of Midway and Kure (Hawaii), where it has been documented that 100% of chicken regurgitations contain plastic (see photo 5) . These high incidences and quantities of plastics are only found in species that live near or within the great oceanic turns, where microplastics accumulate. In this way, these indices help to understand the geographical patterns of marine pollution and their tendency over time.
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