C+S February 2020 Vol. 6 Issue 2 (web)

birdwatchers A new approach to precise positioning helps solve a century-old problem on an isolated island. By John Stenmark

john Houston is not a surveyor. He would be the first to tell you that. He’s not a heavy traveler, either. So what was he doing on a speck of an island in the South Atlantic Ocean, knee deep in brush and muck while operating a high-accuracy GNSS receiver? It’s all about the birds. Houston was at work on Gough Island, a British territory roughly 2,700 km (1,700 miles) west of Cape Town, South Africa. First visited by Portuguese explorers early in the 16th century, the tiny landmass covers just 91 sq km (35 sq mi). Due to its lonely location and un- disturbed nature, Gough is regarded as one of Earth’s least disrupted ecosystems. In 1995, the island was designated as a World Heritage Site by UNESCO (United Nations Scientific, Educational and Cultural Organization). A prime nesting ground for Atlantic seabirds, Gough Island is home to indigenous birds and invertebrates as well as visiting seals and pen- guins. Unfortunately, the birds are in trouble. Houston was there to help. A qualified structural engineer, Houston had travelled to Gough from Derry, Northern Ireland. His employer, Taylor & Boyd Consulting Structural and Civil Engineers, was working on a project for the Royal Society for the Protection of Birds (RSPB) to mitigate a serious threat to the island’s avian population. Houston would support the RSPB efforts by gathering topographic and geotechnical information, including mapping with GNSS. But even advanced GNSS has limitations, especially in such a remote location. Faced with a demanding schedule and tight requirements for accuracy, Houston turned to the Trimble CenterPoint RTX positioning service, which enabled him to conduct high-precision real-time GNSS mea- surements in a challenging and remote environment. Small Animals, Big Problems Aside from brief visits by sealing and whaling vessels in the early 19th century, Gough Island has never had notable human habitation. A handful of scientific surveys, including a 1922 visit by famed Antarctic pioneer Ernest Shackelton, established the island as a valuable site for geological biological and ornithological research. Not until the 1950s, when South Africa established a meteorological station, did Gough Island gain a full time—albeit very small—human population. When Houston and a dozen researchers landed in September 2018, the popu- lation of Gough Island more than doubled. While Gough Island has no native mammals, it has plenty of mice, un- intentionally carried to the island by the 19th-century ships. The invad- ing mice soon learned to feed on the eggs and chicks of ground-nesting

John Houston chats with an albatross. Living on the isolated island, the birds have not developed fear of humans.

birds, including Tristan albatross, Atlantic petrel, Gough bunting, and Gough moorhen. In roughly 150 years on the island, the mice evolved to become 50 percent larger than their forebears. Today they are wreak- ing havoc on the bird population. Surveys by the RSPB estimate that mice consume roughly two million defenseless eggs and chicks each year. “Albatross lay only one egg each year,” Houston said. “If it is lost then they must wait another year for any potential offspring.” At the current rate of loss, Gough Island’s endangered birds face extinction. To protect the birds, the RSPB initiated a project to eradicate the mice John Houston carries the GNSS receiver along a survey line on Gough Island. Cold weather and difficult terrain made days difficult.

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