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Habitat Found: What's Good for the Gull's NOT Good for the Plover By Anne Donovan, CZM When you think of coastal and marine habitats, you probably don't think of landfills. In fact, this unfortunate byproduct of the human habitat certainly does not seem hospitable to anything in nature. But, although these burial grounds for refuse undermine property values in most residential neighborhoods, they are highly prized real estate for one of our most adaptable native birds, the Herring Gull (Larus argentatus). Profile of the Herring Gull The Commonwealth's most typical "seagull," the Herring Gull is a noticeable year-round Massachusetts resident, and is recognized from here to Alaska, summering, wintering, and/or migrating through every state in the United States, except Hawaii. This graceful aerial acrobat of Jonathan Livingston fame is a beauty, whether found at the shore or in a parking lot. It takes four years for a Herring Gull to reach maturity, and before that it goes through nine different plumages, confounding amateur bird watchers with a slate of feather variations ranging from mottled browns and grays to whites. The adult bird is two feet long with wingspan of almost five feet, has an electric-white body, gray wings with black tips, pinkish-tan legs, and a yellow beak, complete with a bright red spot at the tip (which gives gull chicks a cue as to where to peck for a regurgitated meal). Herring Gulls live up to 20 years in the wild and feed on a varied and adaptable diet. Natural food sources include: mussels, crabs, fish (live or dead), sea urchins, carrion (dead animals), insects, eggs, chicks, and even the occasional adult tern or plover. Gulls never pass up an easy meal, however, and large portions of their diet come from garbage, bait and fish waste, table scraps of all kinds, and even sewage. With such a profound capacity to utilize human food sources, the only Herring Gulls that currently still dine on an exclusively natural diet are found on far offshore islands or in remote parts of the low Arctic. Herring Gulls also bring new meaning to "eating on the run" and are capable of consuming their entire daily food intake in 15 minutes flat. Each pair of Herring Gulls, which tend to mate for life, raises one brood a year, although they will lay new eggs if they lose their original eggs or chicks. They build rough nests out of whatever is available, including sticks, grass, feathers, moss, and even trash and other discards. The female typically lays three eggs, which can vary dramatically from mother to mother in color, size, and shape. Chicks take from 24 to 28 days to hatch, are capable of flight in about 45 days, and then stay with their parents for another month. Habitat—More than a Place to Call Home For a habitat to provide all that Herring Gulls need to survive, it must include places to feed, nest, roost at night, and "loaf." Before the bounty of landfills and other human food sources, the gulls' habitat was tied to the coast. Similar to suburban sprawl, however, Herring Gull breeding range has extended inland, following the landfill food source. In fact, in Massachusetts, gulls exploiting landfill leftovers now nest as far inland as the Quabbin Reservoir in the central part of the state, using this and other inland reservoirs for drinking and bathing. One of the few constants with Herring Gulls is that they always nest near water. Generally, they nest in colonies on islands or rock outcroppings. When nesting offshore, they frequently set up housekeeping on flat ground, while mainland nesters favor cliffs, probably to avoid predatory mammals. In some places where human food sources are abundant, they have begun to nest on roofs and window ledges of buildings. (At CZM, we witnessed this behavior first-hand when several pairs of this adaptable bird species built nests on an open wall of a high-rise being reconstructed directly across from our eighth-floor Boston office.) When it comes to nesting, Herring Gulls are communal. They nest in colonies and return to the same place year after year to breed and raise young. Aggression is often the key to breeding success, and pairs will staunchly defend their nest sites from neighbors. If there is a threat from outside, however, the entire colony of gulls will band together to attack a potential predator. Because of their long lifespan and commitment to nesting territories, Herring Gull breeding colonies are virtually permanent once established. As the population in a successful colony expands to fill the available territory, however, young birds are left with no place to nest. These young adults start loafing near a food source, ultimately nesting along a nearby waterbody when their urge to breed takes over. This is the start of a new colony that can expand over time to fill this available territory, assuming the food source is sufficient. Like humans, Herring Gulls are willing to commute, which further expands their range. This commuting capacity was actually studied near Boston in 1961 and 1962 when researchers caught and tagged breeding birds with colorful paint. The gulls were then followed to determine how far they flew in search of food. Not surprisingly most foraged as close as possible to the breeding colony. To exploit choice food sources such as landfills, however, a certain segment of the population was willing to commute great distances, and even a 50 mile round trip was routine. The Human Impact on the Herring Gull through History At one time, the human was not the friend of the Herring Gull. In the 1800s, local fishermen and farmers were eager to supplement their larders with eggs of easy-to-gather ground nesters, including the Herring Gull. (Our resourceful gull did not entirely take this "lying down." In an 1833 visit to Grand Manan, John Audubon noted that the local gull population had taken to nesting in fir trees—and island residents confirmed that these birds had previously nested on the ground.) The situation worsened for the gull and its brethren in the 1880s when fashionable women began wearing feathers in their hats. To satisfy this fad of the time, herons, gulls, egrets, and terns were hunted almost to extinction. In fact, in 1890, the state of Maine actually established a sanctuary for the "endangered Herring Gull" on Great Duck and Little Duck Islands (near Mt. Desert Island). The plight of these birds also spurred the Audubon Society into existence in 1890, with this group successfully bringing the feathers-for-hats slaughter to an end. Once protected, human habitation and habits became a boon for the Herring Gull. These resourceful scavengers first found an abundant food supply in the discards of fishermen and the fishing industry. But the real gravy train was yet to come... The Landfill Windfall Beginning in the mid-1950s, open landfills became a commonplace smorgasbord for the scavenging gull. The result was a population explosion, with Herring Gulls reaching a peak population of 110,000 breeding pairs on the U.S. Atlantic Coast in the late 1970s (up from their relative obscurity at the turn of the century). Since this heyday, the closing of landfills has resulted in a slight decline of population levels (100,000 breeding pairs on the U.S. Atlantic Coast as of the early 1990s). Despite the current dearth of landfills, good times continue for the Herring Gull. The adaptability of this species and the abundant food supply available through other human-based sources, including trash cans and lobster bait, provide a continued competitive advantage for the species. Even its traditional feeding techniques have been enhanced. When once a young gull learned to crack a mussel on a rock, today's young learn to use the endless supply of pavement. In addition, the European green crab (Carcinus maenas), a species likely introduced to Massachusetts waters through international shipping activities, has become a widespread and easily caught intruder that greatly supplements gull diets. Some individuals have even been found to specialize on French fries, hanging out by fast-food dumpsters to snag a high-fat meal. Good for the Gull, Bad for the Neighbors While on the surface enhancing habitat of a native and formerly overly exploited species may seem like a good thing, inevitably, the interference of the human world with the natural cascades into a string of unforeseen consequences. For example, this bloated population of Herring Gulls causes problems for the humans that caused it. Birds loafing on reservoirs foul water supplies with their droppings and have the potential to transmit disease. While flying near airports or otherwise in a flight path, these large birds can pose a threat to aviation. (In the spirit of full disclosure, gulls are not always a nuisance to people. In addition to providing eggs and feathers, gulls have been known through history to help humans. In Germany, for instance, Herring Gull populations were protected because of the abundant fertilizer they provided. Grateful Mormons' have also erected the Sea Gull Monument in Utah after a flock of gulls swooped in to gobble up a plague of crickets that had decimated the Mormon's crops in 1848-49.) Too many gulls also come at the expense of a variety of birds that compete for oceanfront nesting sites, including the threatened Piping Plovers (Charadrius melodus) and endangered Roseate Terns (Sterna dougallii), as well as Common Terns (S. hirundo), which, despite their name, are considered a "species of special concern" in the Commonwealth (which means if their population decline continues, they will become threatened species). Herring Gulls nest earlier than terns and plovers, and this, combined with their size and outright aggression gives them a distinct advantage in the battle for nesting sites. The other birds are forced into less desirable locations where they are more susceptible to predators, further from food sources, and otherwise less capable of successfully raising young. The gull's capacity to eat almost anything also gives them a foraging advantage, allowing them to successfully raise more hungry chicks than the plovers and terns with their pickier palates. In addition, these gulls are successful predators, taking the eggs and chicks of neighboring seabirds (including other Herring Gulls), further reducing the populations of scarcer species. Finally, with the Piping Plover, the very presence of the potentially predatory gull can cause them to pack up and move on. To address this human-induced problem, wildlife managers are trying to provide gull-free nesting areas for the struggling terns and plovers. On Monomoy Island in Chatham, for example, the U.S. Fish & Wildlife Service (USFWS) executed an extremely successful campaign to carve out an 80-acre section of the northern tip of South Monomoy for other birds, particularly terns. In 1996, USFWS staff dropped poison-soaked bread into gull nests, killing 5,000 birds, outraging many animal rights activists, residents, and local officials. For the terns, the effort paid off. Common Terns went from 200 breeding pairs in 1995 to 8,700 by 2003. Populations of Roseate Terns, Laughing Gulls, and Piping Plovers on the island are also improving with the reduced gull pressure. Conclusion: If You Build It, They Will Come (But Others Will Go) Clearly, the development and resource use associated with the human habitat has a profound effect on the animals and plants that also call Massachusetts and its coastal and ocean areas home. In most cases, this land use diminishes and destroys wildlife habitat, but sometimes, like with the Herring Gull, an adaptable species is actually at a competitive advantage because of its ability to cohabitate with humans. The resulting population increase is not a wildlife management success story, however, because it generally occurs at the expense of other species that are not only competing with the successful cohabitators, but also struggling in the face of habitat diminished by human development. These population explosions tend to come at a cost to humans as well, and the heyday of the Herring Gull is no exception, with the resulting threats to drinking water quality and aviation safety. The lessons from our history with the Herring Gull show that the constant motion created by our actions has significant and cascading impacts, benefiting some species sometimes, while harming others. | |||||||||||||||||||||||||||
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