Their fortunes tied to the tides, many species of coastal birds nest directly on the beach. Here Nature seems to conspire against them in these places we so often associate with idyllic relaxation.
On North America’s temperate Atlantic Coast, beaches tend to be sandy, with remains of oyster beds, i.e., oyster rock or shell bank usually serving as the only solid ground. Shifting sands from wind and wave create a wild and dynamic landscape of attrition and accretion. One day there’s a low spot to step over, the next it is a channel to wade through. By the third day it might be connected again.
On barrier islands of our East Coast there is a general zonation from oceanside to mainland. First is the hard-packed, wetted sand of the intertidal zone. This is the denizen of Sanderlings and other shorebirds that hunt for food at the very edge of the surf. As the water recedes with each wave, invertebrates tumble in the foam and tiny holes bubble to reveal morsels just beneath the surface. Sanderlings are masters at pushing their luck to gather as much as they can before the next wave comes in.
Sanderlings are masters at pushing their luck to gather as much as they can before the next wave comes in.
Farther inland the sand is dry. This higher section of the beach – the sort of spot you are likely to lay out your towel – is only submerged during the higher tides and under stormy weather. Weeks can pass without it going under. Most of the time the sand is loose and blows in the wind. Tiger beetles zip across these sands hunting flies and sand fleas. Piping Plovers spend a lot of time here, too and I bet they’re happy to snatch a tiger beetle when they can.
It is just beyond that usually dry sandy zone that a line of debris will accumulate. On a vacation beach, this might get raked away by maintenance crews each morning. On a wild beach it will be Spartina stems, shells, driftwood, fishing nets, and other human refuse that form the wrack line. Here is a line the waves only cross a few times each year, under the highest tides and in the strongest storms. It is behind this line that often can be found a broad, flat area of more densely packed sand and shell with scattered spots high and dry enough to allow some plants like sea rocket and beachgrass to gain a toe-hold.
Beyond this overwash zone the higher dunes form. The sand is loose but held together where plants like sea oats take root. If the dunes are big and stable enough, woody plants could form dense thickets of wax myrtle or even forests of giant loblolly pine. The backside of the dunes flattens to a plain of saltmeadow hay and then to cordgrass saltmarshes that line innumerable muddy channels and inlets marking the bays between barrier island and mainland. Summertime in these marshes is greenhead horseflies and fiddler crabs and the scraping grunts of Clapper Rails. The saltmeadow hay is home to Seaside Sparrows and clouds of mosquitoes hungry enough to bite right through your jeans. If there is a forest zone of myrtle and pine, it will also be choked with poison ivy and crawling with ticks so abundant that some of the deer have ears that hang like a hound dogs’ from the loss of turgor and weight of all the blood suckers latched on. Here where change is the most conspicuous constant, the line between paradise and worst nightmare is defined by a few centimeters of elevation or a shift in the wind.
Here where change is the most conspicuous constant, the line between paradise and worst nightmare is defined by a few centimeters of elevation or a shift in the wind.
It was into this bewildering world that I, native of a landlocked hillside hundreds of miles inland from the coast, found myself immersed in the summer of 1990. For my master’s research in the Department of Biology at the College of William and Mary, I studied beach-nesting birds – specifically terns, skimmers, and gulls – on barrier islands along the coast of Virginia’s Eastern Shore. The Nature Conservancy manages all or part of 14 of these islands as the Virginia Coast Reserve in Northampton and Accomac counties, protecting a 55-mile stretch of Atlantic coastline in as pristine a condition as can be hoped for in the 21st Century.
The islands have also been the focus of a Long-Term Ecological Research project headed by the University of Virginia. Hog Island has been particularly well-studied, both for its ecological and historical significance – it once supported the thriving town of Broadwater, VA, most of which was reclaimed by Mother Atlantic in the 1930s. Hog Island is where I was on 14 June in 1990: Dropped off at the south end, and slowly marching myself north through the sand to my rendezvous point at the former Machipongo Coast Guard Station 4 miles and several hours north.
I was drawn to Hog Island for two reasons. First, I could get there. Folks from the Virginia Coast Reserve had agreed to drop me off and pick me up as convenient to their daily rounds supporting the LTER work. Second, I needed an island that had nesting terns, but not nesting gulls.
Beach-nesting terns occur in colonies of a few to thousands of pairs. There’s a lot of research that has addressed why they nest in colonies, with the needle variously pointing toward group defense against predators and the comings and goings of neighbors helping birds find ephemeral food sources (i.e., shoals of small fish close to the surface) more efficiently. They might place some nests in the low dunes themselves, but mostly they target that area between the wrack line and the dunes for nesting. Closer to the water they run a greater risk of flooding; deeper into the dunes and they might face other problems like ghost crabs or those clouds of mosquitoes. It is those overwash zones that attract the beach-nesters. There they can place their simple nests of a scrape in the sand with some bits of shell that hides their cryptic eggs and nestlings so well. From there, they can rapidly take off to forage in the ocean during daylight hours or, for Black Skimmers, to the still waters of the bayside tidal creeks at dawn and dusk.
If you’re keeping score, our beach-nesting birds are already on a knife edge (in the skimmers’ case, rather literally).
To collect food they need small fish close to the surface. Terns will fly maybe 10 or 20m above the water and dive in to catch their prey. They only go a bit deeper than their sharp bills can reach, however. If the fish aren’t close to the surface, then they aren’t going to be tern food. What’s more, they can’t hunt that well if the seas are rough so I bet there are plenty of stormy days each year that they just hunker down and don’t even try to go fishing.
It’s even worse for skimmers. Uniquely, these birds fly with shallow wingbeats very close to the surface of still waters and slice though the surface with the distal half of their elongated lower mandible. When they detect a small fish they instantly jerk their head down that grab it with both mandibles. (If you can picture yourself catching tiny fish between the blade edges of two butter knives – while flying and relying only on your sense of touch – then you’re unusually good at imagining what skimmer foraging is like!) Skimmers generally hunt the still tidal creeks, and at dawn and dusk when the waters are their most calm. The old watermen sometimes call them “night-strikers”. When they fly past you there is a sublime zipper-like sound created by that lower mandible cutting the surface, followed by a little snap and a splash when they catch something.
So it takes a lot of learning and skill for these birds to catch their food. That food is patchily distributed in both time and space. The total abundance of that food is subject to everything that affects fish stocks in general: water pollution, overfishing, oil spills, DDT, water temperature, etc. This is the essence of the information center hypothesis of group living. A tern flying back to its nest with a fish for its chick or its mate is a clue as to where fish can be found. Another individual can observe the direction from which that bird came (or simply follow it on its next foraging run) and greatly increase its efficiency in finding fish to catch. The more birds nesting near you, the more information you can gather about where the good fishing is at any given time.
Speaking of those nests, they’re rather vulnerable. A scrape in the sand of an overwash between the wrack line and the primary dune? This is the definition of exposed. One decent coastal storm and entire colonies can be lost to rough seas and a high tide. A couple of cool, rainy days early in the season can easily lead to hypothermia for eggs and nestlings, or even an incubating adult. By summer, an air temperature of about 90F (32C) on a sunny day can translate to a surface temperature of about 120F (49C). Vulnerable eggs and nestlings can roast fairly quickly under conditions like that. They’re subjected to these conditions for (data for Common Tern) 22–27 days of incubation and another 20–31 days in the nestling/juvenile stage. At a minimum these birds are exposed to all manner of dangers for 42 days, and something like 58 days might be more likely. I’ll split the difference and say 7 weeks. Beach-nesting birds need about a 7 week window of no floods, plenty of food, warm but not too warm and, oh yeah, protection from predators.
When you nest in the open on a beach, anything that would like to snatch an egg or a nestling from you is a serious threat. Coyotes, foxes, raccoons, bobcats, domestic cats, rats, mice, and even ghost crabs will raid your nest. From the air, common predators include hawks, falcons, Great Horned Owls, Fish Crows, Boat-tailed Grackles, gulls, and American Oystercatcher. Nests are also vulnerable to inadvertent disruption and trampling from off-road vehicles, humans chasing off-target Frisbees, and happy doggos fetching tennis balls absent-mindedly tossed by their hoomans in the direction of nesting birds. There’s a long history of intentional persecution too, with entire stuffed terns once adorning ladies’ hats. Truly painful are the more modern stories of intentional human destruction, such as the teenaged boys who infamously gathered eggs from a tern colony on a public beach in New York and tossed them in the hair to hit with their whiffle ball bat. That one still pains me to write about. In July 2018, beachgoers just off Dauphin Island in Alabama evidently piled tern eggs in one spot to clear out a space for volleyball. I wish I was making that up.
Nestling Black Skimmers (above left) and Common Terns (above right) illustrate the vulnerability of life as a beach-nester.
A trifecta of nest predators for beach nesting terns and skimmers.
There are two ways to protect the investment of your nest when you need a 7-week window on an exposed beach. You can hide it or you can defend it. Piping Plovers are great hiders. Their eggs, nests, chicks, and adult selves disappear against a background of sand and shell. If you approach a bird on the nest, it will invariably see you long before you see it, and the adult will hop off the nest and lure you away from it. Unless you are very lucky, it’s difficult to find a Piping Plover nest without a lot of time and effort spent in search of it, and 2–4 tiny eggs isn’t really that great a prize.
Terns and skimmers have cryptic eggs and nestlings, too. The adults, however, are noisy and conspicuous. The noisy colonies are easy to find with birds flying out to forage and back all day long. There’s also the acrid scent of guano on the air. The nests might be cryptic, but the colonies are beacons. The cryptic coloration of eggs and young might buy a little time but these birds have evolved a different nesting strategy than the Piping Plovers. They opt for group defense. As you approach a colony, alarm calls increase to deafening and all the adults take flight. They swirl around you and harass you with repeated screeching fly-bys and an aerial assault of guano. Some of the terns will be bold enough to made bloody contact between their rapier bills and the top of your head. The more birds in the colony, the more terrifying an experience this is for the would-be nest raider but, like everything in nature, there are trade-offs. The biggest colonies, e.g., thousands of birds in multi-species aggregations, put up the most vigorous defense but they’re also the biggest beacons and the pressure from predators is relentless. In those colonies, there is pressure to build a nest in the best-protected center. A Johnny-come-lately on the periphery might ultimately decide to try some smaller colony where the group defense will be weaker but the predation pressure won’t be constant.
The nests might be cryptic, but the colonies are beacons.
Mother Nature seems to conspire against them. Life for breeding terns and skimmers is a complex set of gambles on exactly where to start a nest each spring. The only thing going for them is longevity. These birds might have 20 or more summers of breeding attempts in their lives, and they only need to be successful in a few seasons to produce enough offspring for a decent chance that at least two will survive to replace their parents in the population. Their fate might look dismal in any given year, but it’s the lifetime reproductive success that really matters.
Even the ghost crabs are ready to pounce on a young bird that is weakened or unwary.
All of which returns me to Hog Island in the summer of 1990. There, several smaller colonies of Common and Least terns – along with the more mild-mannered Black Skimmers – had established themselves on oceanside overwashes. Their most prevalent nest predators were Laughing, Herring, and Great Black-backed gulls, but they were relatively safe from these bullies. Laughing Gulls nested on the bayside in the cordgrass lining the tidal creeks. Herring and Great Black-backed Gulls nested on low dunes and isolated high spots within overwash areas on the oceanside, but there were no gulls nesting on Hog Island that summer. Thus, even though the tern colonies supported just a few dozen pairs, they had the benefit of seeing a potential gull predator coming from (in many cases quite literally) a mile away. Every so often a gull would cruise by, the tern and skimmers would raise the alarm, and the group defense would effectively see the gull off before it got anywhere near the birds’ nests. It worked.
Or at least it worked for a bit. During my first visit to Hog Island on 15 May, a lot of birds were still moving north. Terns and skimmers were checking out the overwash areas, but no one was actually nesting yet. Any that had started around that time were soon thwarted by the massive coastal storm and high tide flooding that swept the coast a few days later on May 22nd. At Cobb Island just south of Hog, my notes for May 23rd include the word obliterated. The prevalence of 2-egg clutches among the nests I found on 14 June suggest that this was indeed a second nesting attempt for most of the birds, as 3-egg clutches are more typical for first attempts in a season. By 3–4 weeks after the big coastal storm, things were looking up for the beach-nesters and eggs were starting to hatch. The terns remained aggressive in their defense of the colony.
By the 3rd week of June, some individual nests had been depredated, but the two colonies were still intact. Then came violent storms on July 1 and July 11, both with storm surges that washed out almost every remaining nest. In fact, I found several new nests on July 11, from birds trying yet again following the July 1 storms. But on the night of the 11th and even worse storm blew through. By July 17, there was no significant nesting being attempted on Hog Island. Terns and skimmers had been washed out there at least three times since May. During my last survey that summer on August 1, fall migration was underway. A few terns might have been successful with raising a baby to independence on Hog Island that summer, but in general that breeding season was a bust. It was a total loss for nesting Black Skimmers. To me it was a magical, windswept, stifling, brutal time. For Hog Island’s terns and skimmers it was just another roll of the dice with hopeful lessons learned for their next chance, next spring.
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eBird checklists and notes from the 1990 field season on Hog Island
Hog Island, Northampton, Virginia, US
Jun 14, 1990 9:45 AM – 6:15 PM
Comments: South-to-north survey of nesting terns and skimmers on the ocean side of Hog Island. I mapped 7 discrete colonies this cool and somewhat rainy day. No nestlings. All nests ranging from scrapes to 3-egg clutches.
Herring Gull 1
Least Tern 38 minimum – did not count birds at two of the colonies
Common Tern 44 minimum – did not count birds at two of the colonies
Black Skimmer 80 minimum – did not count birds at two of the colonies
Jun 19, 1990 9:00 AM – 2:00 PM
Comments: Continued placing markers near nests of mixed tern/skimmer colony found on 14 June just north of the Red Onion building in the private inholding on Hog Island. First nestling observed this day (Common Tern). My disturbance in the colony attracted two Laughing Gulls and three Fish Crows, but these were chased off by the Common and Least terns.
Laughing Gull 2
Herring Gull 100 Loafing on the northeastern corner of the island, well away from tern colonies
Least Tern 12
Common Tern 16
Black Skimmer 74
Fish Crow 3
Jun 20, 1990 9:00 AM – 2:00 PM
Comments: More marking nests and monitoring colonies of Common and Least terns with Black Skimmer. Following nests of 15 Least Tern and 25 Common Terns in two different areas. At least 5 nestlings found today; nest defense quite vigorous by terns. Black Skimmers present but quite passive in defense.
American Oystercatcher 1
Laughing Gull 1
Herring Gull 1
Least Tern 30
Common Tern 58
Black Skimmer 100
Fish Crow 1
Jun 21, 1990 9:00 AM – 3:00 PM
Comments: Worked the southern colony on Hog Island this day, with 7 Least and 18 Common tern nests checked. The colony is a loose aggregation of nests spread out over a N–S distance of about 120 m. The species are segregated with the Least Tern nests on the south side of the Common Tern nests. I observed Common Tern chasing from the colony Great Black-backed Gull (twice), Northern Harrier, and Herring Gull. Least Terns chased out Laughing Gull and American Oystercatcher.
Northern Harrier 1 Observed daily on Hog Island. On this day, I observed a Common Tern chase one away from the nest colony on the south end of the island.
American Oystercatcher 1
Laughing Gull 1
Herring Gull 1
Great Black-backed Gull 1
Least Tern 32 14 in southern colony; 18 in northern colony.
Common Tern 58 38 in southern colony; 20 in northern colony
Jun 26, 1990 9:30 AM – 2:00 PM
Comments: Five days elapsed since my last nest checks. At the north colony there was one new Least Tern nest with 2 eggs, but 5 other nests were now empty. It’s possible that in that time the eggs hatched and the nestlings subsequently moved deeper into the dunes to seek shade. However, for the first time this season, I found Herring Gull tracks in the colony. I also found the remains of a depredated Least Tern adult. Its headless and wingless body suggesting raptor (Northern Harrier, Peregrine Falcon, or Great Horned Owl) predation. I also cut my activity short after noting some heat-stressed nestlings in the colony. (Generally, I would dash in and collect the data I needed in about 10 minutes and then wait an hour before disturbing the birds again.)
Herring Gull 1 Injury to back of head evident by a dark smudge of dried blood.
Least Tern 19
Common Tern 30
Jun 27, 1990 9:00 AM – 4:00 PM
Comments: Beach-nester monitoring today plus whole-island surveys with Barry Truitt, Ruth Beck, Michael Beck, Steve Rottenborn, Kelly Paine, Joe Mersereau, and Mary Mersereau.
American Oystercatcher 2
Least Tern 31 Some nests in both colonies flooded and/or depredated. Two sets of human tracks through the southern colony. No gull prints in colony but tracks of American Oystercatcher and ghost crab near some disturbed nests.
Common Tern 48 Some nests in both colonies flooded and/or depredated. Two sets of human tracks through the southern colony. No gull prints in colony but tracks of American Oystercatcher and ghost crab near some disturbed nests.
Black Skimmer 121 Birds loafing on the beach, away from the colonies.
Jul 6, 1990 10:30 AM – 4:00 PM
Comments: With Steve Rottenborn today. Last check was 27 June; big coastal storm came through on July 1. This was my first chance to get to Hog Island since that storm. Most nests in both colonies were washed over from the storm tide on July 1. Just a few terns and a lot of gulls hanging around today.
Laughing Gull 73
Herring Gull 127
Great Black-backed Gull 24
Least Tern 4
Common Tern 10
Jul 11, 1990 8:45 AM – 4:00 PM
Comments: Whole-island survey today with Ruth Beck, Caren Caljouw, Kurt Buhlmann, and Chris Pague. Now 10 days after the storm tide flooding from July 1, beach-nesters are trying again with multiple new nests and birds at every stage from making new scrapes to feeding the handful of chicks that survived the storm.
American Black Duck 8
Brown Pelican 90
Great Egret 19
Snowy Egret 17
Little Blue Heron 2
Tricolored Heron 6
Black-crowned Night-Heron 1
Yellow-crowned Night-Heron 1
Glossy Ibis 157 Most observed along bayside marshes.
Northern Harrier 1 Northern Harrier bred on Hog Island in 1990; birds observed most days.
American Oystercatcher 57
Black-bellied Plover 12
Piping Plover 15
Semipalmated Sandpiper 2
Laughing Gull 124
Herring Gull 164
Great Black-backed Gull 21
Least Tern 40 In three separate areas now; 12 nests in the south colony ranging from 1 egg to 2 nestlings. There were 8 nests in the north colony: 2 with 1 egg and 6 with 2 eggs. One dead Least Tern found; some egg shells apparently depredated by oystercatcher.
Gull-billed Tern 9 Two adults each hanging around north and south colonies – perhaps making scrapes – but no evidence of nesting beyond that.
Common Tern 60 Just 3 nests appear to have survived flooding at south colony; 4 nests remain at north colony. Nine new nests at southern colony, however: 6 with 1 egg; 3 with 2 eggs. Also 4 new nests in between the colonies, associated with new skimmer nests.
Forster’s Tern 9
Royal Tern 17
Black Skimmer 228 More than 100 adults hanging around the main north and south colonies. I found 16 nests at the south colony this day: 11 with 1 egg and 5 with 2 eggs. An additional 14 nests have been initiated at the new colony.
Jul 17, 1990 8:45 AM – 1:15 PM
Comments: Whole-island (beach side) survey with Steve Rottenborn and Bill Williams.
Most recent survey was 11 July, and we wrapped up the day with storm clouds gathering. That night, violent storms tore through the area and very likely washed the new tern and skimmer nests that had been established following the 1 July storm. Just a handful of birds still actively nesting or caring for young. Widespread eggshell fragments and tracks of American Oystercatcher, gulls, ghost crabs, small mammals, and a large passerine (Boat-tailed Grackle or Fish Crow) in the colonies.
American Black Duck 10
Surf Scoter 1 Sorry no details other than diagnostic pattern of white and black observed on face.
Brown Pelican 87
Great Blue Heron 1
Great Egret 20
Snowy Egret 6
Little Blue Heron 3
Tricolored Heron 3
Black-crowned Night-Heron 3
Glossy Ibis 29
Northern Harrier 3
Clapper Rail 6
American Oystercatcher 24
Semipalmated Plover 9
Piping Plover 8
Red Knot 5
Least Sandpiper 9
Western Sandpiper 3
Short-billed Dowitcher 9
Greater Yellowlegs 1
Lesser Yellowlegs 1
Laughing Gull 503 Many offshore following fishing boats.
Ring-billed Gull 4
Herring Gull 377
Great Black-backed Gull X
Least Tern 44 South colony had 11 adults and no fledglings or active nests. There was 1 fledgling and 4 chicks at the north colony, with 27 adults hanging around. Lastly, 4 adults were at the north end of the island with one 2-egg nest.
Gull-billed Tern 7
Caspian Tern 1
Common Tern 85 At south colony, 38 adults but just 3 nests remain (2, 1-egg nests and 1, 2-egg nest). We found 1 Common Tern chick and 1 abandoned egg at the north colony.
Forster’s Tern 32
Royal Tern 27
Black Skimmer 147 Most of the skimmers (136) were at the south colony but there were no actives nests there. At the north colony, 11 adults were hanging around but there was just one errant skimmer egg in the colony.
Eastern Kingbird 1
Fish Crow 15
Purple Martin 1
Tree Swallow 1
Barn Swallow 93 Individuals steadily moving south today. You only see one or two at a time.
Seaside Sparrow 1
Aug 1, 1990 9:00 AM – 4:00 PM
Comments: Final beachside whole-island survey of summer 1990 with Ruth Beck and Steve Rottenborn. I pulled my nest markers today as there were no more active nests in either the north or south colony. All Black Skimmers had left the colonies; just 14 Common Terns remained hanging around the south colony. Least Terns included 5 adults and 1 fledgling at the south colony and 4 adults with no nests at the north.
Large numbers of shorebirds on the move south.
Incidental: found a dead leatherback sea turtle today; this one appeared to have scars from propeller damage.
Blue-winged Teal 2 Sorry no details, but large number of dabbling ducks on fresh/brackish ponds.
American Black Duck 92
Red-breasted Merganser 1
Pied-billed Grebe 3
Brown Pelican 20
Least Bittern 1
Great Blue Heron 1
Great Egret 9
Snowy Egret 14
Little Blue Heron 8
Tricolored Heron 3
Glossy Ibis 39
Northern Harrier 2 Sorry, no details on age and sex.
Clapper Rail 5
American Oystercatcher 9
Black-bellied Plover 109
Semipalmated Plover 213
Piping Plover 11
Ruddy Turnstone 11
Red Knot 105
Sanderling 1232 Shorebird migration in full swing!
Least Sandpiper 2
Semipalmated Sandpiper 121
Western Sandpiper 19
Short-billed Dowitcher 220
Spotted Sandpiper 1
Greater Yellowlegs 18
Lesser Yellowlegs 5
Laughing Gull 170
Ring-billed Gull 20
Herring Gull 200
Great Black-backed Gull 8
Least Tern 13
Gull-billed Tern 4
Caspian Tern 3
Common Tern 26
Forster’s Tern 8
Royal Tern 19
Black Skimmer 1
Mourning Dove 1
Peregrine Falcon 1
Fish Crow 13
Horned Lark 11
Northern Rough-winged Swallow 1
Tree Swallow 17
Barn Swallow 309 Birds steadily moving south throughout the day. We only counted the birds that passed us moving south – and that was pretty much all of them.
Carolina Wren 1
Gray Catbird 2
Prairie Warbler 6
Seaside Sparrow 5
Song Sparrow 10
Eastern Meadowlark 12
Brown-headed Cowbird 4
Boat-tailed Grackle 5