Black-headed Gulls and Great Black-backed Gulls: Birdwatching in the Scottish Hebrides, Part 4
Dr. James J. S. Johnson
For the earth shall be filled with the knowledge of the glory of the LORD, as the waters cover the sea.(Habakkuk 2:14)
The islands of Scotland’s Outer Hebrides are a familiar territory for various seagulls, including two in particular: (1) the largest seagull, the low-sounding “laughing” Great Black-backed Gull (Larus marinus); and (2) a much smaller yet loud-“laughing” Black-headed Gull (Larus ridibundus, a/k/a Chroicocephalus ridibundus).
Great Black-backed Gulls are large (more than 2’ long, with wingspan about 5’ wide; often males weigh up to 4 or 5 pounds, while females weigh slightly less), deserving their nickname “King of Gulls”. Thanks to God-given toughness these gulls can survive and thrive in coastlands of the North, breeding in parts of Russia, Scandinavia, along Baltic coasts, the British Isles, Iceland, Greenland, the Faroe Islands, plus the Atlantic seacoasts of Canada and America’s New England shorelines. In winter many of these gulls migrate south.
In Nornian, the ancient Old Norse-derived language of the Shetland Islands, the Great Black-backed Gull was once called swaabie, from swartbak, meaning “black back”—whereas in AD1758 Karl (“Linnaeus”) von Linné taxonomically designated theseseagulls as Larus marinus, denoting a marine seagull/seabird (from Greekλάῥος). In a previous study (titled “Birdwatching at Staffa, near Iona: Puffins, Shags, and Herring Gulls”), the Great Black-backed Gull was noted as a prominent predator of Atlantic puffins, yet this gull avoids puffins who nest near humans.
However, it is not just the Atlantic puffins that must beware the apex-predatory pursuits of Black-backed Gulls, because these gulls also prey on terns and many other birds, as well as almost any other organic food smaller than themselves, living or nonliving, if they can swallow it. Accordingly, these scavenging gulls are attracted to garbage dumps filled with human wastes, as well as to egg-filled nests of smaller birds, plus available rodents (e.g., rats) and lagomorphs (e.g., rabbits). Likewise, these bullies practice “klepto-parasitism”, i.e., aerial bullying-based robberies of food from other birds—when accosted by Great Black-backed Gull, the smaller birds drop their food—as the Great Black-backed Gull chases the dropping food, to capture it in the air, the robbery victim flies away to safety.
During the winter months these gulls spend less time over land, because the sea itself then offers better opportunities for food—especially lots of fish! Any fish who are close to the ocean’s surface are at risk when these gulls scout for catchable food. In fact, quantitative studies of their stomachs show that marine fish (such as herring) are the primary diet of Great Black-backed Gulls, although they also eat other birds (like herring gulls, murres, puffins, terns, Manx shearwaters, grebes, ducks, and migrant songbirds), plus small mollusks (like young squid), crustaceans (like crabs), marine worms, coastline insects and rodents, as well as inland berries, and lots of garbage and carrion (found in places as diverse as saltmarshes, landfills, parking lots, airport runways, piers, fishing docks, surface ocean-waters, etc.).
[See William Threlfall, “The Food of Three Species of Gull in Newfoundland”, Canadian Field-Naturalist, 82:176-180 (1968). See also, accord, Kirk Zufelt, “Seven Species of Gulls Simultaneously at the Landfill”, Larusology (http://Larusology.blogspot.com/2009/11/7-species-of-gulls-simultaneously-at.html ), posted Nov. 15, 2009.]
Like the above-described Great Black-backed Gull, the gregarious (i.e., colony-dwelling) Black-headed Gull is notorious for its omnivorous scavenging and often-predatory habits, opportunistically frequenting oceans, intertidal beaches and estuarial coastlands, marshlands and other inland wetlands, lakes, rivers, and even agricultural fields. These gulls, as breeding adults, sport dark-chocolate (almost black) heads.
Black-headed Gulls can soar high in the air, swim in the ocean, and walk along a sandy beach—they are equally comfortable moving to wherever they want to go to. These noisy seagulls sometimes appear to “laugh” when they call. Like other seagulls, they enjoy eating fish—sometimes they dip their heads under the tidewater surface, while swimming. When scouting along a coastal beach, these gulls probe for coastline critters (which they probe for and snatch). Also, they are fast enough to capture flying insects, which they catch “on the wing”.
Gulls come in many varieties, plus some of these varieties are known to hybridize. For example, Great Black-backed Gulls (Larus marinus) hybridize with Herring Gulls (Larus argentatus). Black-headed Gulls (Larus ridibundus) often hybridize with Mediterranean Gulls (Larus melanocephalus), and also with Laughing Gull (Larus atricilla) and Common Gull (Larus canus). Other hybrids exist, too, and many of these gull hybrids have been verified by genetics (i.e., DNA parentage verification).
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[ As a boy this author watched seagulls, both inland and at seacoasts, with wonder. God made them all! A half-century later, I still watch seagulls (and many other birds) with wonder. “He (God) does great things beyond searching out … and wonders without number.” (Job 9:10) — God shows how wonderful He is! ]