Tag Archives: ecology

Brandt’s Cormorant Diet Studies

—– Written for (and cross-posted from) the excellent Point Blue Conservation Science Blog – Los Farallones —–

My internship at the Farallones involved many different fascinating studies, but one of my favorite studies were the seabird diets, as they really tie in the oceanographic aspect of marine ornithology. We are lucky to be able to live on this incredible, rugged island surrounded by the Pacific ocean and work with the birds that call it home, but sometimes it can be easy to take for granted just how strong the connection is that these birds have to the marine environment. By incorporating the feeding ecology of the seabirds, we are also considering vast topics like oceanic health, fisheries ecology, and climate change, much of which is still poorly understood. Taking part in studies that delve into this mysterious, watery realm is pretty exciting. Brandt’s cormorants also happen to be one of my favorite birds on the island – how could you not love the silky black birds that look like Muppets with long necks and giant feet, and whose eyes are a vibrant, deep turquoise?


Male Brandt’s Cormorant in full display glory

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Seabirds and Rats

With a dual interest in the seemingly distantly related fields of marine biology and ornithology, seabird ecology emerges as a definitive choice of study for me personally.  As the synthesis of my two favorite areas of science, it also has the potential to extend into other fascinating fields of study involving conservation biology, resources management, island ecology, biogeography, fisheries, oceanography, evolution, and behavioral ecology – all of which are topics of import on their own, but framed through the lens of seabird ecology, present expansive research opportunities.

rats' eye view of Witchcraft Point, Kiska Island, from the deck of the Tiglax

rats’ eye view of Witchcraft Point, Kiska Island, from the deck of the Tiglax

I find myself most engaged by topics that address the interplay between components of ecological systems. In many ecosystems, seabirds play a vital role of connecting the biomass of the oceans with those on land. They act as conduits of nutrient transport, therefore playing vital roles in the ecosystems they are part of. On many oceanic islands, terrestrial life would not be sustained without the activity of nesting seabirds. Since many oceanic islands (especially in the Pacific) are volcanic in origin, they were never close enough or connected to land masses from which mammals, crawling insects, reptiles, etc could colonize. This made them blank canvases for birds who could simply fly across vast watery moats – and in so many cases, avian life dominated many remote islands and through the raw power of evolution, adapted to fill a wide variety of niches. With the lack of land predators, there were many instances where birds simply lost their ability to fly. Of course, as humans came to dominate the planet and expand across it, many islands were discovered by sea-faring groups. This was unequivocally bad news for the islands’ bird species, especially those flightless ones. Many avian species were extirpated within a short period of time after human discovery, falling as easy prey. Another important issue that came later was the introduction of other species to islands – goats, pigs, cattle, cats, mice, and especially…rats. Invasive rats have been inadvertently introduced through human activities to about 90 percent of the world’s islands. This statistic is almost unbelievable. Even more scary is the result of these invasions: they are responsible for approximately 50% of all island bird and reptile extinctions. Thus it is not surprising that Norway rats present a serious and ongoing threat to seabirds in the Aleutian Islands. They have invaded entire islands, introduced through human shipping activities. Currently there are about a dozen islands where rat populations are established, and consequently bird populations on those islands have been decimated. The first invasion event in the Aleutians was likely a Japanese shipwreck in 1780, where everyone but the rats perished. Rats are especially harmful because they breed quickly, can eat pretty much anything, and do so opportunistically – including seabirds, their chicks, and their eggs. On many islands this was catastrophic, wiping out a significant portion of crevice- and burrow-nesting seabirds like auklets, storm-petrels, and puffins during their short summer breeding season. The worst thing the rats would do is not just killing to feed, but indiscriminately killing dozens of birds and eggs in one haul.

adult Least Auklets and eggs from a rat cache from Kiska Island (pic from Natl Geographic)

In fact, the group of Aleutian islands immediately to the east of Buldir are called the Rat Islands because of their overwhelming domination. Buldir itself has been kept rat-free thanks to its isolation and distance from any nearby islands where rats might colonize from. Buldir sits in the middle of a shipping lane between Russia and Asia. We would frequently see massive container ships pass by on the horizon. Just from the frequency of passes, the risk for rat invasion is relatively high. Weather in the Bering Sea is notoriously challenging, and an average of two ship incidents happen a year. Rats are certainly inhabitants on almost all of these vessels, and they know when to leave a sinking ship. Fish and Wildlife appropriately has a “rat spill” team that responds to sinking ships, attempting to prevent any swimming rats from reaching shore using floating barriers. The communities on the populated Pribilof islands of St. Paul and St. George proactively maintain an island defense network against rat invasion. The native Tribes offer rat prevention kits to fishing vessels that visit harbor, and local fish processing businesses are required to have rat prevention systems in place. Rat traps are deployed and maintained in harbors and dumps – and in over 15 years, they have caught 6 rats this way, meaning that there is indeed movement of rats from ships in harbor onto the islands.

A bit of good news: the Rat Islands have been the site of a successful rat eradication campaign that resulted in the declaration of one of the islands (now re-named Hawadax, Aleut for “those two over there”) completely rat-free in 2009. This was the result of a tremendous cooperative and costly effort between the US Fish and Wildlife, The Nature Conservancy, and Island Conservation. The entire island was basically heavily treated with poisoned rat bait…and it seemed to have worked.

Human effects, both direct and indirect, are having consequences on seabird populations around the world. Few people come into direct contact with seabirds, and yet through various activities (seafood consumption, plastic use/abuse, climate change, invasive/introduced plants and animals, pollution, oil spills), most species are suffering from consequences exerted by humanity.  Seabirds can seem to be so far removed from human activity that some people are baffled at even the idea of a “seabird”.