Colonization and Conservation of the Green Heron on Bermuda,
the Result of Partnerships in Species and Wetland Restoration
By Terrestrial Conservation Officer, Jeremy Madeiros.
The Green Heron (Butorides virescens) is a new addition to the nesting avifauna of Bermuda. The first successful nesting was documented in 2002; and by 2006 and 2007, the number of Green Heron nests on Bermuda stood at about 20 annually at up to seven sites. At least three of these would now qualify as important bird areas for the species in Bermuda. Further details of the Green Heron’s recent colonization of Bermuda may be found in Wingate et al. 2009. Given that Bermuda had only 10 native nesting bird species, the Green Heron’s addition to the avifauna is a significant event for the nation’s biodiversity. Moreover, natural colonization of an island is a rare event and one that is seldom documented, so it is significant that this colonization has been thoroughly documented by the Bermuda Audubon Society (BirdLife in Bermuda) and the Department of Conservation Services whose partnership in species and wetland conservation over the years were most likely responsible for the successful colonization event.
While early colonial records suggest that several species of heron were nesting on Bermuda in pre-colonial time, the cumulative impact of human settlement over 400 years, with a human population now standing at 65,000 on an island of only 54 Km2 (21 miles2 ) has had a dramatic effect on native waterbirds. Hunting by protein-challenged colonists no doubt began the process of waterbird decline. Then over the centuries, most wetland habitats were destroyed through dredging and/or reclamation for farmland, industrial sites and solid waste disposal. These two processes together appear to have been responsible for the elimination of resident heron populations, as there were no confirmed records of heron nesting between the advent of scientific documentation of Bermuda ornithology in the mid 19th century and the mid 1970’s.
Similarly, two processes appear to have been responsible for the return of herons to Bermuda. The first was a species conservation program, the deliberate introduction of the Yellow-crowned Night Heron (Nyctanassa violacea) in 1976-78 as a substitute for the endemic night heron that had been exterminated at the beginning of human settlement Bermuda. This introduction took well, and the night heron established a number of nesting colonies in remnant wetlands and offshore islands. In that Bermuda has always served as a stop-over or wintering area for North American herons, potential colonizing stocks of other heron species were available but did not stay to nest. The presence of the Yellow-crowned Night Heron likely facilitated the colonization of the Green Heron as a nesting species, enticing wintering birds to stay on into the summer nesting period. Green Herons first nested in sites already occupied by nesting night herons.
Successful establishment of the Yellow-crowned Night Heron was achieved concurrently with extensive wetland conservation measures. These measures were initiated in the 1950’s when two local non-government conservation organizations, the Bermuda Audubon Society and the Bermuda National Trust, began to lobby government to end the destruction of wetlands and launched fund raising drives to acquire, restore and manage those wetlands that remained. Their efforts were later bolstered by Government initiatives, the most important being protective zonings and the cessation of garbage dumping in the marshes after 1983. Bermuda is now a party to the Ramsar Convention (through UK ratification) and seven wetlands have already been declared as Ramsar sites. Others are proposed. Restoration and management measures, most notably the culling of invasive exotic species, are being undertaken by a Conservation Unit within the Department of Conservation Services.
Since 1950 more than half of Bermuda’s remaining wetlands have been acquired from private owners and managed as nature reserves. Restoration efforts on them have resulted in the creation of eight new ponds with nesting islets and nine other open water areas including water trap ponds and irrigation reservoirs on golf courses. As this type of habitat is optimal for Green herons, it seems highly probable that these conservation efforts have been a major factor enabling their recent colonization. The story might not end there as several other regularly visiting heron species have the potential to colonize. Further other waterbirds, notably coots and moorhens, have clearly benefited from the wetlands as their nesting populations have grown and become more widespread.
The species management and intensive wetland conservation efforts on Bermuda, involving close cooperation between local NGO’s, the Government, and private land owners, provide a shining example, applicable to the wider Caribbean where many of the most important wetland areas are also in private ownership and species conservation is a necessity.