Kevin T. Karlson
Posted: April 9, 2013, 4:15 p.m. PDT
Beach-nesting birds face many challenges as human development eats up the places where they nest and raise chicks.
The dog bounded effortlessly down a deserted stretch of barrier beach as its owners, leash in hand, enjoyed a leisurely walk. Unnoticed by everyone, including the dog, were several species of shorebirds and terns until they suddenly went airborne to emphatically protest the presence of this four-legged predator. Another sharp-eyed resident of this deserted beach habitat, a Laughing Gull, observed the whole scene and was already moving to take advantage of the situation. Swooping in with surprising speed and grace, this opportunistic predator grabbed a young Piping Plover chick that had been left unprotected by its distracted parents and flew off to enjoy a morning meal.
Scenes like this are occurring with increasing frequency as previously untouched expanses of remote beaches are accessed by numbers of four-wheel-drive vehicles and their drivers and passengers. Visitation to these areas by people trying to "get away from it all" during the summer nesting season is just one of many factors that have cumulatively resulted in serious population declines in several species of beach-nesting birds.
The Problems Facing Beach-Nesting Birds
Along the coastlines of the United States, especially isolated barrier beaches and offshore islands, certain specialized birds have successfully evolved with the natural biology of these coastal habitats. A delicate balance between food availability, predatory pressure and the ever-changing geography of coastal habitats was achieved over many nesting seasons.
As the human population increased during the 20th century and development encroached upon these coastal areas, this delicate balance was disturbed. Besides the presence of humans and their pets (dogs and cats are major disturbances to beach-nesting birds) in these fragile beach habitats, there also was an increase in several animals that benefit from humans, particularly red foxes and raccoons. The unnatural increase in fox and raccoon numbers can be devastating to the success and survival of beach-nesting birds if these mammals migrate to coastal areas in search of food. Both raccoons and foxes have an incredible sense of smell, and if they locate an easy food source like bird eggs and chicks, just one pair can wipe out most of the nests in their territory. They also may persist as an annual threat to the survival of the birds in these locations, which might eventually eliminate certain species that return to the same area each year to nest.
Colonial nesters like Black Skimmers, and Least and Common Terns stand a better chance of distracting or driving away these predators than solitary pairs of shorebirds, such as Piping Plovers and American Oystercatchers, which may nest in the middle of wide expanses of beach. Extraordinary protection measures for nesting Piping Plovers, such as enclosure nest cages and low-voltage electric wires, have been implemented and revised over the last decade as population numbers continue to decline.
Unlike American Oystercatchers, which also nest in difficult-to-access coastal marshes, Piping Plovers have very specific habitat preferences of open beach and adjacent back dune areas, and they are especially susceptible to predators and general disturbance. On some New Jersey beaches, Piping Plover numbers have declined so drastically that all vehicular traffic has been banned during the nesting season.
Another human-related threat to the survival of beach-nesting birds is the increased use of recreational all-terrain vehicles like dune buggies. These vehicles can bring even casual day trippers to the most remote beach locations, which historically were free of significant disturbance. Besides the threat of crushing well-camouflaged bird eggs, these vehicles may cause birds to flush from their nests, leaving eggs and chicks exposed to the deadly sun and aerial predators like Laughing, Herring and Great Black-backed Gulls.
These gulls have always taken a small percentage of eggs and chicks, but the numbers taken today are much higher due to increased human-related disturbances. Gull numbers, especially Laughing Gulls, have dramatically grown in proportion to human habitation, as our waste products in garbage dumps and sewage outflows provide a steady year-round food source.
All these problems are recognized by biologists, but sadly there is no end in sight to increased human encroachment. Consequently, Piping Plover, Black Skimmer and Least Tern are presently listed as endangered in New Jersey as well as many other states. It is generally understood that we must somehow learn to live side by side with these special beach-nesting birds to give them a chance at survival. Conservation measures and public education are at the forefront of our efforts.
This distinctive ringed plover of central and eastern North America has achieved notoriety in recent years but for less-than-popular reasons. Many favorite Atlantic Coast beach sites have been closed during the months of June and July to protect this endangered species, resulting in more than a few public protests against this tiny shorebird. Hard facts suggest that unless we reverse some of the increased disturbance of critical coastal habitats, Piping Plovers will disappear from traditional locations, possibly forever. Although many people are inconvenienced by restrictions to summer beach getaways, this special shorebird has become an indicator of the success of our efforts to save important natural ecosystems from overdevelopment and irreversible damage.
Piping Plover become a barometer for the well-being of our coastal habitats.
A tiny plover (7 inches) in the genus Charadrius, Piping Plover is very pale above and blends in perfectly with the sandy habitat where it resides year-round. This camouflage plumage protects the species from predators, especially avian ones, but it also can result in crushed eggs and chicks by unsuspecting vehicles and even human feet. Piping Plover is difficult to spot on a sandy beach, even to the trained eye, and most mishaps with humans are unintentional.
Piping Plover nests on sandy beaches along the coast or on inland lakeshores, preferring areas with scant vegetation. However, inland populations continue their steady decline, and most of the hopes for saving this federally threatened species lies with Atlantic Coast nesting colonies. Results from careful studies conducted by the New Jersey Division of Fish, Game and Wildlife, Endangered and Nongame Species Program have shown about a 22 percent decline in Piping Plover from 1990 to 1999 but an approximate 10 percent increase from 1987 numbers. This increase is a result of nest site protection from disturbance. It is difficult to pinpoint the exact reason for the decline, but a combination of the factors outlined above are probably appropriate.
Although not a communal nesting species, numbers of Piping Plover may nest close to each other in preferred coastal locations. Typical nests consist of four eggs carefully placed in a shallow scrape in the sand. Camouflage is the best defense against predators, as the cryptic eggs blend well with the open sand. Adults will perform distraction displays to draw intruders away from the eggs and chicks, often feigning a broken wing when danger is sensed.
Precocial Piping Plover chicks leave the nest within 24 hours and journey to the water's edge to feed themselves. The adults will brood and care for the chicks until they fledge, which takes about 24 days. During this time, the flightless chicks are most susceptible to predators and vehicular dangers, such as the deep ruts caused by tires. These ruts act as traps and barriers for the young chicks that must walk to the water's edge to feed.
Because of its noncommunal nest behavior and inability to adapt to other habitats, Piping Plover faces continued pressure to its survival in coming years. They have become a barometer for the well-being of our coastal habitats
Once thought to be closely related to gulls and terns, Black Skimmer is now understood to be quite different and belongs to its own family of three worldwide skimmer species. The only skimmer in the Americas is the Black Skimmer with its long bill — the knife-like lower mandible is longer than the upper. This is a unique feature to skimmers, and it benefits the species in its feeding habits. It flies low over the water, primarily at night when fish are feeding close to the surface, with the lower mandible cutting through the surface of the water. When fish or other prey strike the lower mandible, it snaps shut, trapping the food in the bill.
A steady decline in Black Skimmer numbers has resulted in the listing of the species to endangered status in New Jersey.
Unlike Piping Plover, skimmers nest in tight colonies — one colony in New Jersey (1993) numbered more than 1,500 individuals! These highly social birds have survived over the years with their selection of offshore islands and remote peninsulas as nest sites, but these areas are also in danger because of increased human visitation and development. Another recent problem is the occurrence of frequent winter storms, which has altered the shifting coastline and destroyed some historical nesting areas, forcing the skimmers to relocate to less secure locations. A steady decline in Black Skimmer numbers has resulted in the listing of the species to endangered status in New Jersey, with conservation measures being undertaken by state wildlife biologists.
There are few sights as graceful and breathtaking as a flock of Black Skimmers flying in formation while skimming for food. This species has fine-tuned basic survival skills to ensure the success of its breeding colonies.
After inspecting and resting in a prospective breeding location for up to a month, the birds begin nest site selection after pair bonds have been formed. These bonds come after countless display flights and duels, culminating with the offering of a fish by the male to the female. If she accepts this offering, copulation takes place and egg laying begins.
Each skimmer pair establishes a small territory for a nest site and drives off any intruder, including other skimmers. The size of the nest location determines the density of nests in a given area, with some colonies having nests only a few feet apart.
Adult Skimmers of both sexes bring fish to the chicks and aggressively attack anything that comes too close to them, including other adult skimmers. These attacks can be quite savage, sometimes resulting in injuries. New Jersey biologists have documented Black Skimmers killing young chicks that made the mistake of venturing into a neighboring nest site.
When chicks start to mature, nurseries will form, with numbers of skimmers acting as guards for the flightless chicks. These "guards" will collectively drive off any aerial predator with swift, aggressive attack flights. They also attack other skimmers from the same colony that come too close to the nursery. These aggressive attacks against other skimmers consist of agile aerial maneuvers, during which the skimmers twist and turn in the air, all the while loudly barking their distinctive vocalization.
As the young skimmers fledge and are able to fly, the adults teach them how to skim by flying close to the colony and demonstrating the feeding technique. The young birds mimic the adults by running along the water's edge while putting their lower mandible into the water. After a while, the young birds try their luck at this very specialized feeding habit while in flight. Until they are successful, the adults continue to feed them. When all the birds have fledged, adults and juveniles remain together in the same area but not necessarily at the colony site. They gather in large numbers at a chosen location in late fall, and then migrate to more southerly regions for the winter. Black Skimmer nests along the Atlantic Coast, from Massachusetts south through the Gulf Coast to northern Brazil, and on the Pacific Coast from Southern California and the Salton Sea south to Ecuador.
This diminutive white tern with a yellow bill is the smallest tern in North America, with an average length of 9 inches. A cosmopolitan species, it breeds in colonies at marine and freshwater locations. One subspecies breeds from California south to Mexico on the Pacific Coast, while another breeds in the interior U.S. from Iowa south, and on the Atlantic Coast from Maine south to Florida, through the Gulf of Mexico and Caribbean Sea to Venezuela.
This tern flies with hurried wingbeats, at times resembling a shorebird in flight. It hovers in the air before plunging into the water for food. Once several pairs of Least Terns choose a suitable location for nesting, dozens more may be attracted to the site, and a sizable colony may form. If successful for several years, the colony may grow to a very large size.
The Least Tern with its yellow bill is the smallest tern in North America, with an average length of 9 inches.
After a beach replenishment project created a large area of sparsely vegetated open sand habitat in Monmouth Beach, New Jersey, a colony of 225 Least Terns nested there in 1996. In 1997, the numbers grew to 600, in 1998 to 739, and in 1999 to 868. Although seemingly high, this number represented almost half of the Least Terns counted in the entire state.
While this area grew dramatically, other historical sites nearby reflected much lower numbers, indicating that many birds relocated to this new colony. From 1990, when 2,261 birds were counted in New Jersey, numbers have dropped to lows of 1,627 in 1992 and 1,310 birds in 1996. The last three years recorded numbers of Least Terns just above or below 2,000 individuals, which seems to be the stable point for the last decade.
Besides being affected by all the human-related problems mentioned for Piping Plover and Black Skimmer, Least Tern has a preference for nesting just above the high tide line at coastal locations. This precarious habitat selection often results in the loss of an entire colony's eggs and flightless chicks due to surging ocean waters related to summer storms, early hurricanes or unusually high tides.
One encouraging factor involving Least Tern is its ability to adapt to environmental changes by selecting alternate secure nest sites. In south Florida and the Florida Keys, I have observed numerous Least Terns nesting on flat roofs of buildings in large shopping centers located near the ocean or other large bodies of water. These birds are safe from human and mammalian disturbance and also from storms and ocean surges. However, these birds face a completely new problem: sometimes flightless juveniles leap from the building edge to a paved surface below. Even if the young birds survive the fall, the busy location would prevent adults from feeding them.
In large nesting colonies, I have observed both parents leaving their one or two chicks to fly off in search of food. When they returned, neighboring chicks had often mixed with their own, and recognition of young did not occur. The adults ended up feeding the chicks that were closest to where they last left their own, without realizing they were from another tern pair. Unlike skimmers, which are keenly aware of their own young, Least Terns may end up caring for the young of their neighbors until they have fledged and can find food on their own.
American Oystercatcher & Common Tern
These two species, one a shorebird and the other a larger tern, are not listed as threatened at this time but share the same fragile nesting habitat as the three species highlighted above.
American Oystercatchers feeds its young until the chicks' beaks are strong enouchgh to crack open the shells of the crusaceans they prey on.
Common Terns often nest at the edges of large colonies of Black Skimmers, often joined in the general vicinity by numbers of Least Terns. These three species collectively form a large, frenetic colony, where each species take turns attacking each other, depending on which one feels crowded at the time. An uneasy truce exists in these shared colonies, as all three species will drive off avian predators together, and will aggressively attack humans or mammals that venture too close to the nest location.
At a shared colony in Stone Harbor, New Jersey, two pairs of oystercatchers had chosen a large expanse of beach on a remote peninsula for their nest sites in early May. By mid-June, they were surrounded by 500 aggressive Black Skimmers, 30 Common Terns and more than 200 Least Terns. Every time the oystercatchers were flushed, numerous attacks by all three species occurred as the large shorebirds tried to get back to their nests. The other three nesting species viewed this unusual shorebird as a potential threat, as it walked into the large colony instead of flying back to the nest.
Even though the oystercatchers were there first and the other species had moved in around them, relentless attacks occurred every time they returned. The oystercatchers tried to defend themselves by spearing the diving birds with their powerful bills, but I never saw a successful strike. Nevertheless, both oystercatcher nests hatched successfully, and the family groups fledged five chicks in the following weeks.
Common Tern are a global travelers, flying great distances to winter in South America each year.
American Oystercatcher is very different from all other nesting shorebirds in North America (except for American Woodcock), in that it feeds its young until their bills have sufficiently developed to crack open the shells of crustaceans that make up their major food source. They also remain as a family group through the first winter, unlike most other shorebirds that leave their chicks before they have fledged to migrate south. These family groups have formed large gregarious flocks of up to 300 birds that have spent the last few mild winters in New Jersey, feeding in the productive back bays.
Common Tern, on the other hand, is a global traveler, flying great distances to winter in South America each year. Noted for its aggressiveness when defending a nest colony, Common Tern has been known to draw blood from the scalp of unwary biologists who wander too close to the nests. There are no easy answers or solutions to the problem of declining beach nesters, but state and federal biologists are working very hard in their attempts to balance the lives of these birds with those of humans and animal predators. Countless volunteers and nonprofit organizations, such as The Nature Conservancy, are also working to educate the public about these problems and how we can make a difference in this life-and-death drama that unfolds every year virtually right at our feet. Public education is an important starting point for expanding our conservation efforts to preserve the natural beauty that our shrinking planet has to offer.