Every year at the beginning of July, when Bermuda’s waters became warmer in the summer sun, a crimson migration erstwhile passed over our roads and beaches. Side-ways bumbling land crabs in their thousands used to make for the water, in some places crossing over busy south shore roads. On the stretch between Spittle Pond and John Smith’s Bay, cars couldn’t help but crush the animals on their way to spawn. Cantankerous land crabs were in houses and on roads – and on golf courses it was jokingly easy to get a hole-in-one in their numerous burrows.
Naturalist Dr. David Wingate also has his own land crab memories, “in the 1970s, when my palmettos were up, and starting to flower and produce berries on Nonsuch, the land crabs would climb up the palms and clip off the berries, and the other crabs would be waiting on the ground for them.” Dr. Wingate did not wish to affect the ecosystem of his nature reserve with the use of poisons, and so the land crabs were even more abundant there. Most of the castor pumice organic fertilizer, which he lugged up from the beach and distributed on his plantings with buckets, became food for vast numbers of crabs.
One of his early jobs at the department of Agriculture was to mix poison for golf courses in an attempt to control the crabs, which were an economic concern with their incessant burrowing. Though the devastating effects of DDT would not be discovered until later – and in fact Dr. Wingate would do much to ban the poison by showing that it affected even the eggs of Cahows, a bird found nowhere near the fields where it was sprayed – it was in frequent use in Bermuda at the time. In general, the land crab was regarded by the public as a pest.
And they were – the land crabs could be said to be as numerous as ants. They lumbered over shorelines and traversed tree roots, with deep red carapaces and wise, unblinking eyes; the ground seemed to be swelling with the crabs’ tiptoeing. The fight for survival demands prey to eat, and for them to be eaten – so why was nothing eating the crabs? They gallivanted about, holding summer revelries on flat, open golf course greens that no other crab would dream of, for fear of being spotted by the watchful eye of a crab-eating predator.
Dr. David Wingate’s research could offer an answer. His most major project was his ‘living museum’ on Nonsuch Island, which was designed to be an accurate picture of pre-colonial Bermuda. Not only would Nonsuch be free of the invasive species that humans had brought to Bermuda over the years, but the environment it created would also hope to restore populations of organisms that dwindled on extinction after early settlers had hunted them.
In order to research what kinds of birds would have been present in pre-colonial Bermuda, Dr. Wingate undertook extensive cave explorations in an effort to find fossil bones. “The number one species I found were the Cahow – some caves were absolutely riddled with Cahow bones,” Dr. Wingate notes, but he also found something else – the complete skeleton of a night heron in a sink hole cave, which had probably fallen in and been unable to get back out of the small opening above.
By working with avian paleontologist Dr. Storrs Olson to describe the bones, Dr. Wingate found that the pre-colonial heron in Bermuda was clearly derived from the Yellow Crowned Night Heron. In order to restore a pre-colonial ecosystem, the modern Yellow Crowned Night Heron was the only option. They would control the “super abundant” populations of land crabs, as Dr. Wingate characterized their vastness, by stabilizing them to levels that they should have been at all along. It seemed the reason that they had exploded so far out of control was because the early settlers had decimated populations of their predatory heron.
Meanwhile, Bermudians had become concerned with the crab’s impact on crops, as they ate vegetation voraciously. The economic impact of their continued landscaping on golf courses was also significant, and when the reintroduction of the heron was presented to the Board of Agriculture, the response was overwhelming.
Dr. Wingate quickly got hold of Yellow Crown Night Heron babies from a nest in Florida. The hatchlings were raided from the nest at a young age and shipped in an aircraft with Dr. Wingate personally back to Nonsuch. To his delight, they were easy to hand rear, and the scraggly chicks were soon turning into graceful fledglings.
“It became an exciting thing to do, for my volunteers to catch land crabs. We stored them in a lovely old, stone bathtub that was from Government House, and fed them tins of dog food to keep them healthy until they were fed to the herons.” Dr. Wingate noticed that, far from needing to be hand fed, the herons instinctively knew to peck at the offered crabs. Once they fledged, they saw the land crabs coming out in the evening and began hunting them for themselves.
Dr. Wingate notes that the Yellow Crowned Night Heron normally eats crayfish, an animal smaller and with less dangerous pincers than the land crab’s bulky claws. He says that they are clearly not adapted to eating the crabs, as their bills are too narrow. For a Bermudian Yellow Crowned Night Heron to eat a crab, it’s a big production that can take up to thirty minutes. The heron shakes the crab vigorously until the crab autotomizes – they have the ability to shed their limbs as a distraction in order to make an escape. But the crabs are too slow and cumbersome to do so, so the heron simply catches them again and shakes them until they are left with the body. “There is one extra step the herons have to do,” Dr. Wingate says – they turn the crab’s body on its side and rear their head up and strike down on it so the hard carapace is knocked off and they’re small enough to swallow.
Interestingly, the exact problems that the Yellow Crowned Night Heron has in eating a land crab, were accounted for in the skeleton of the extinct night heron. The extinct herons had shorter legs, which were more suited to terrestrial hunting, and a wider bill, which would have enabled them to swallow land crabs with ease. “It was a bit unfair to take a crayfish-eating heron and dump it where land crabs are the only available prey,” Dr. Wingate chuckles, but without the original night heron available, the Yellow Crowned Night Heron was the best alternative to fill their place.
After wintering on Nonsuch in the first year, the herons quickly spread to the mainland. Dr. Wingate was initially concerned with the herons’ breeding success on such a densely populated island, as Yellow Crowned Night Herons like to nest far away from people. However, he explained, due to the influence of man upon the environment, he had had no reason to be concerned – the woodland of Bermuda had become so drastically altered by invasive species that it was impenetrable. “You can’t walk in a thicket anymore,” he explains, sadly.
He explained that while Bermudian native plants were naturally selected to withstand hurricane winds, invasive species are no match for them. Even in death, sturdy cedars provided a backbone for the forest, by holding invasives up. When invasive plants had outcompeted sustainable natives, and most of the cedar timber had been harvested illegally, the woodland fell in on itself and became too dense to be accessed. “The Brazil pepper is the worst for that,” he said, referencing its tendency to sprawl in a horizontal woody tangle.
As a result, there seemed no limits on the Yellow Crowned Night Heron, who promptly set to work feeding on the abundant and naïve land crab, and breeding in Bermuda’s thickets. “Herons are colonial nesters,” he says, which means that they are triggered to nest when they see other herons nesting. As soon as one population of herons was nesting here, another one quickly began – the Green Heron, which colonized without human intervention. Dr. Wingate hopes that we may even achieve a nesting population of Great Blue Herons in time.
“Nesting birds are safer in Bermuda than they’ve ever been,” Dr. Wingate notes. Because of increased awareness about the importance of conservation, he has noticed a respect for the natural world that was not present a few decades ago. Whereas Dr. Wingate struggled to find volunteers in the early years of his Nonsuch project, and oftentimes people found it to be an inconceivable idea, now individuals all want to know how one man’s dream brought a seabird back from extinction. With mixed emotions, he also notes that children spend much less time outside exploring nowadays, instead absorbed in their phones or computers. On one hand, this leads to less disturbances of the natural environment – as Dr. Wingate says, “most of the boys when I was growing up would go through a phase of abusing wildlife, stoning birds, meddling with longtails.” On the other hand, it reduces the public’s involvement and curiosity with the natural world, which could lead to a damaging inertia.
While the Yellow Crowned Night Heron’s introduction to Bermuda was successful in restoring the land crab population to pre-colonial, sustainable levels in the ecosystem, public opinion of the crabs was beginning to change. Where people had found them simply to be a nuisance before, fishermen started protesting at their absence.
“It’s a well known Bermudian fishing tradition – you’d go and dig up a few crab holes, and use them as bait for hogfish,” Dr. Wingate explains, and fishermen ended up excavating nature reserves on the hunt for the diminished crabs. At this time, conservationists began to become concerned that herons would totally exterminate the land crabs.
The land crab shows many characteristics of a highly predated animal. In their journeys by moonlight to reproduce, they release thousands and thousands of eggs, which hatch almost immediately after they hit the water. Then, the tiny crablets, smaller than a fingernail, climb out of the water and back up the cliffs to mature. The production of so many offspring is a tactic by animals with high mortality rates – all of their young are never expected to survive, only a tiny percentage. A similar vastness of progeny can be seen in turtles, because 90% of turtle hatchlings are hunted before they leave the beach.
The land crab was a prolific spawner, because it had to be in order to have any hope of continuing as a species, but in the absence of even one predator, those spawning levels had high success rates, and rocketed populations to the profuse colonies observed at one time in Bermuda.
In addition, the crabs normally dwell in burrows, which is a tactic to minimize their exposure to herons. Dr. Wingate noted that the reason land crab populations seem less abundant than they really are is because the crabs have learned not to venture out of their burrows unless there is a good reason. They are able to feed from the burrows on rootlets, and risk predation by herons if they spend too much time on the surface.
However, even this did not account for the land crab’s dramatic decline. “I was really surprised that the land crab became so much rarer than I thought it would. I asked myself, what are the other factors?” Dr. Wingate postulated on various factors besides predation affecting land crabs, exploring the introduction of cars to Bermuda, the urbanization of Bermuda, and the introduction of the kiskadee.
“Cars are a huge factor,” he said. “Now that the island is motorized, there’s no way that remaining crabs would make it across to the beach. With the amount of traffic now, you’ve essentially wiped out crabs living on the inland side of any public road.”
He then told me about an interesting dinner he’d had at the Southampton Princess’ Whaler’s Inn. “There was a big commotion among the dinner guests – and suddenly there was this big land crab there, laden with eggs.” A guest picked it up and went with Dr. Wingate to set it down near the shoreline, where a crowd saw it perform the characteristic ‘shimmy-dance’ to release its eggs.
“I thought, what chance does that crab have of getting back through all of the obstructions?” He explained that the restaurant was surrounded by sheer, concrete walls, which the crab would have had trouble climbing back up, and that coastal properties now populated much of the island. Urbanization also has the effect of adding artificial light, which could disorient the crabs if they use the moon to guide them to the sea, as turtles do, he noted.
Dr. Wingate also suspected that the invasive kiskadee, which he had tried to warn the island about introducing, was likely targeting tiny crablets when they made their vulnerable journey from the sea back onto land. “The population of kiskadees in Bermuda is probably about 10x their native range,” he said. He explained that while populations of Yellow Crowned Night Herons probably don’t exceed 500 birds, kiskadees are numerous, and probably responsible for the extinction of the Bermuda Cicada, which used to be superabundant. If they’re targeting crabs now, that could explain their dramatic decline.
“The crab has not become extinct and I don’t expect that it will, because of its reproductive strategy,” Dr. Wingate assures. “If you go up to Alfred Blackburn smith reserve – it’s a real coastal wilderness up there – if you walk the trail there, you can still see land crabs at reasonable density. They’re not how they used to be, at a foot apart, but you can find burrows that are ten or twelve feet apart.”
“They were more abundant than they were supposed to be at that time,” Dr. Wingate says of the height of land crab population density. “Had the herons not become extinct, no one would have seen that relationship because crabs would have been moderately common and herons would have been along the golf courses like they are today.”
The positive effects of the Yellow Crowned Night Heron’s introduction to Bermuda are clearly seen, as a healthy ecosystem will have a high number of predators, which regulate prey animals. In time, a more diverse range of species will also inhabit the niches that land crabs previously monopolized. “There’s a case of reintroducing a predator increasing biodiversity,” Dr. Wingate says, as he explains that Bermuda hermit crab populations are expected to increase over time, because the land crabs were competitors with them for food.
There is some ethical debate surrounding biological controls, and indeed interfering with the ecosystem at all. There is an argument to be made that because humans are animals too, we should view our effects on the ecosystem as natural. In contrast, Dr. Wingate believes, “we have so tampered with nature globally now that basically we’ve been acting like irresponsible Gods. Because of the damage we’ve done I think we’re obligated as a species to help nature to recover.” Luckily, interest in conservation has skyrocketed in the last few decades, and more and more people are seeking to right the environmental disruptions we have caused. “The biggest enemy to conservation in Bermuda has been the Bermuda Environmental Ministers,” he said, though he was impressed by the attitude of the public.
Dr. Wingate emphasized the huge number of factors that go in to the creation of a sustainable ecosystem, and how altering even one of them could cause the entire thing to unravel. Especially on oceanic islands, where ecosystems are small and fragile, you never know what changing one thing could effect. This was certainly the case when early settlers hunted the night heron to extinction, and it is only now, when we have seen the effects of a similar predator upon the ecosystem, that we can see its restorative power. The Yellow Crowned Night Heron has kept crab populations in check, which has enabled our ground vegetation to grow more lushly. Aside from the relationship of the two original species, it has also affected others – opening up an opportunity for hermit crabs to thrive in their niche once again, and for other species of heron to colonize Bermuda.
Although he has retired from the Nonsuch project, Dr. Wingate continues to do ornithological research. When I spent time with him in his Harbour Road house, he said he was working on a paper on the common tern nesting population in Bermuda, which is heavily affected by stronger hurricane action due to global warming. He has also begun overseeing a Nonsuch-esque project on Trunk Island. Through pure research, and conservation and education efforts, Dr. Wingate is still a powerful advocate for the environment in Bermuda.
He tells me that he is eighty-three years old in October, and living in Bermuda all that time; he notices the long-term effects of pollution upon the environment. He is concerned about the effects of global warming, and maintains that we as a species must continue to work towards a more sustainable world. “Man is a product of nature, he is a part of nature, and he has to learn to live with it.”