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Sea Birds and the Changing Sea

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The oceans on our planet are in a state of change and the change may not be good for seabirds. As global temperatures rise, sea levels and sea temperatures rise, and the oceans become more acidic. These changing conditions have caused a cascade of decline in the marine food web.

As our atmosphere warms, glaciers and snowpacks melt, and the added water and the subsequent warming (thermal expansion) of the water cause the rise in sea levels. Scientific research indicates sea levels worldwide have been rising at a rate of 0.14 inches (3.5 millimeters) per year since the early 1990s (National Geographic). Terns and many other seabirds nest on low-lying sites that are prone to flooding as the seas rise. Many seabirds have a high level of site fidelity; they are hard-wired to return to the same nesting site, even if the site will be flooded by sea water.

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Sea Birds and the Changing Sea:Enter your sightings in eBird: Red Billed Tropicbird. Photo by Charles Shipley
Enter your sightings in eBird: Red Billed Tropicbird. Photo by Charles Shipley

Warming has occurred from the surface of the sea to a depth of about 2,300ft (700m), where most marine life thrives, and the top layer is now getting warmer at a rate of 0.2°F per decade (US Environmental Protection Agency). Plankton, a diverse group of sea organisms, hold up the bottom of the ocean food chain. Plankton is an important food source for krill and other fish that are staple foods for many seabirds and sea mammals (whales and dolphins). Research has shown that warming seas significantly decrease both plankton and krill populations. Cooler water holds more oxygen and, in general, colder seas are more productive. As water warms, productivity of the entire marine food web declines. Warming is reducing the basic amount of food produced by oceans.

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Sea warming is also changing the proportions of what lives in the sea—the ratio of sardines to anchovies, for example (Audubon Magazine). Research has shown that the direct cause for the breeding failure of common guillemots, Arctic skuas, great skuas, kittiwakes, Arctic terns and other seabirds at Shetland and Orkney colonies in the UK was a shortage of small fish called sandeels, a crucial prey species for the seabirds (World Wildlife Fund). Many seabirds are specialized feeders and fail to adapt to changing food supplies, or if they do the replacement food is not as nutritious as the lost food.

Sea Birds and the Natural Sea:Rising sea temperatures are making it difficult for some seabirds to find enough food
Rising sea temperatures are making it difficult
for some seabirds to
find enough food

Even small shifts in temperature, chemistry or salinity can have cascading effects. Oceans have become more acidic due to the increased levels of carbon dioxide – the same cause for acid rain.

When water (H2O) and carbon dioxide (CO2) mix, they combine to form carbonic acid (H2CO3). Carbonic acid is weak acid, but still affects many organisms, especially those that build shells, which are made of calcium carbonate and are weakened by acid. There are two major types of plankton that build shells made of calcium carbonate that are important to the marine food chain. The acidification of the oceans creates unfavorable conditions for plankton, krill, fish, and shellfish. Meanwhile jellyfish are benefitting from the warmer more acidic oceans. As you can imagine, coral are also negatively affected by ocean acidification.

HELP Needed to Record and Report Sea Bird Sightings

Sea Birds and the Natural Sea:Global Sea Temperatures. Graphic courtesy of NAOA
Global Sea Temperatures. Graphic courtesy of NAOA

As an individual it is hard to stop climate change. Do what you can by investing in solar and wind power to lower the carbon footprint of your boat or home. You can, however, help monitor seabird populations by observing seabirds at anchor or on passages. Do your best to identify the bird, or take a photograph of the bird. Record the date, time and latitude and longitude, such as by taking a follow-up photo of your chartplotter screen and then enter your observation in eBird (www.ebird.org), the database for Cornell Laboratory of Ornithology. If you cannot identify the bird or enter the data ask for help on the *Birding Aboard Facebook page listed at the bottom of this article. Additional resources, including instructions and tally sheets, can be found in the Files under the Banner photo. This citizen science data is an important resource for scientists and citizens worldwide and is shared with other conservation organizations.

There are several good bird identification guides for the Caribbean: Birds of the West Indies, by Herbert Raffaele, and A Field Guide to the Birds of the West Indies, by James Bond (Peterson Field Guides).



Devi Sharp is a retired wildlife biologist who spent eight years cruising the Caribbean with her husband Hunter on their sailboat, Arctic Tern. Devi and Hunter are now living on dirt in Western North Carolina.

Chuck Shipley is a former professor of computer science and an avid amateur photographer. Chuck and his wife Barbara live aboard their trawler Tusen Takk II in the Caribbean.

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Devi Sharp is a retired wildlife biologist and exploring the Caribbean with her husband, Hunter, on their sailboat Arctic Tern.

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