To ensure accuracy while conducting bird census, biologists and scientists developed a cost-effective methodology by employing unmanned aerial vehicles (UAVs) or drones. The traditional way to count burrow-nesting seabirds was time-consuming and not very accurate. Also, it disturbed the birds’ habitat, raising serious questions about ornithological ethics.
The outcome of the experiment can turn out to be a landmark as far as seabirds’ conservation is concerned as the estimated detection error of the census is 5.6 percent only.
Scientists, associated with institutes from Mexico (Universidad Autónoma de Baja California Sur. La Paz, B.C.S.) and Italy (Ornis italica), used drones to estimate the population of black-vented shearwater (Puffinus opisthomelas) on Natividad Island, Mexico.
The Island is home to 95 percent of the global seabird population. It is brown and white-breasted with a smudgy face and neck, often found off the west coast of North America.
According to the International Union for Conservation of Nature (IUCN), an international organization that works for nature conservation and sustainable use of natural resources, over 40 percent of 365 seabird species are listed as the most threatened bird taxa. The BvS is listed as near-threatened on the IUCN Red List.
The IUCN reasoned that large-scale competitive commercial fishing, pollution, and human disturbances are a threat to these birds. In the past, feral cats had also threatened the bird species.
The census
UAVs were used for the first time by scientists to census burrows and birds. The technology provided aerial images, giving new perspective that can be re-examined multiple times as other methodologies are both costly and can adversely affect wildlife.
Nest counting
According to a research paper — A new use of technology to solve an old problem: Estimating the population of a burrow nesting seabird — published in 2018 in Plos One journal, scientists made multiple visits to the sites. The first two visits were to calibrate their UAV methods, while the third visit was for data collection for the burrow census. Besides, they had also carried out ground-truthing to estimate error detection. For this, scientists randomly selected 20 circular plots (each area 60 sq. m) and matched it with aerial images that UAV captured from a height of 30 meters.
The experiment used a Chinese-made UAV, where a standard camera gimbaled on to avoid vibration effects and was pointed downwards in parallel to flat ground, was flown at 2m/sec, and a photograph was taken every five seconds.
Occupancy estimate
Scientists used ground-based methods to estimate the occupancy of burrows in selected 25 quadrants of 400 sq. meters. These quadrants are categorized into the high density of burrows (more than 18 burrows), medium (between 12 and 18), and low density (less than 12 burrows). Scientists used toothpick methods to detect occupancy. They deployed toothpicks at the entrance of burrows in the evening, and if the toothpicks were down, they assumed to occupied burrows.
Later, Burrow-scopes were used, which were manned with a sensor, LEDs, and a lens, to detect ‘real occupants’ — as sign of reproduction and non-breeder as ‘apparent occupancy’.
Cost and risk
The new method estimated the population of BvS at 37,858 and 46,322 breeding pairs for 2016 and 2017, respectively.
The method is cost-effective and will drastically reduce the cost of additional UAV-based surveys. Besides, it certainly reduces the time by more than a half and increases the accuracy over the traditional method.
However, the new method might pose a potential predation risk to other birds such as ravens and gulls.
