How dead birds, old maps are helping scientists track biodiversity loss

The Nilgiri mountains in the Western Ghats are a biodiversity hotspot, home to a diverse array of birds, mammals, plants, and other life forms. Called the ‘blue mountains’ because of the blooming of Strobilanthus flowers, the Nilgiris are home to many species that are endemic and of conservation concern, including the Nilgiri pipit, the Nilgiri sholakili, and the Nilgiri laughingthrush.

In a study recently published in Global Change Biology, Vijay Ramesh and a team of scientists from institutes in India, the UK, and the US explored how changes in land use in the last 170 years affected the diversity of birds in the Nilgiri mountain range. The team compiled data from two sources: museums and field-based surveys.

‘Lack of recognition’

First, they digitised geographical information from birds collected by British ornithologists in the late 1800s and which are preserved in natural history museums. Then they revisited and surveyed 42 of the same sites where historical surveys took place. The team also digitised a historical land-use map and compared it with current satellite images.

In this way, the team found that the relative abundance of almost 90% of grassland birds in the Nilgiris has dropped. The Nilgiri pipit and the Malabar lark — both of which are restricted to grassland habitats — in particular had suffered the steepest decline.

Likewise, the team analysed GIS-based land-cover change to show that the extent of grasslands had decreased by 80%: from 993 sq. km in 1848 to just 201 sq. km in 2018.

However, to their surprise, the scientists also found that the abundance of about 53% of forest birds has been relatively stable in the last century. This is because much of the grassland habitats had been replaced over time by wooded forests — in the form of either exotic plantations or woody invasive species — in response to increasing temperature. This switch allowed forest-dependent species a new, alternative habitat, keeping their abundances stable, the team argued.

“Perhaps the biggest threat is the lack of recognition of grasslands as an important part of the landscape. People in the landscape understand this; however, the wider efforts are always targeted at conserving forests and planting trees,” V.V. Robin, an author of the paper and associate professor at IISER Tirupati, said.

An important repository

Beyond the findings themselves, the study’s methods are notable. They highlight the sort of innovation researchers can resort to in order to elicit new ecological and conservation wisdom. While field-based studies remain invaluable to understand the natural history of a habitat or species, data collected decades ago provides historical context to current biodiversity baselines. Historical data allows researchers to make comparisons across a longer time period, which isn’t possible with field studies.

Natural history museums are a particularly important repository of such historical data. While many such museums around the world have a reputation for wowing visitors, the latter often engage with only a small fraction of specimens. The vast majority are in fact stored in large, climate-controlled facilities that are maintained by a team of curators, biologists, and facility managers. These are animals that naturalists had collected over centuries from around the world.

“Museums are vital for biodiversity research, especially in India, a global hotspot of species diversity,” Pritha Dey, a moth biologist and head of the research collections facility at the National Centre for Biological Sciences, Bengaluru, said. “They preserve historical records of species distributions, help in taxonomic identification, and provide baseline data crucial for conservation, climate impact studies, and tracking biodiversity loss over time.”

Scientists have used records from museums to describe many new species, understand the migration of birds, document changes in animals’ body sizes in response to climatic changes, and to elucidate the collapse of entire communities of birds. In the new study as well, the researchers examined specimens of birds collected in the early and late 1800s, which were preserved along with data about their location, the date on which the specimen was collected, and by whom.

With the number of specimens of each species from historical and modern periods, the scientists used a new Bayesian statistical method called field abundance—museum abundance (FAMA). This method allowed the researchers to estimate the relative abundance of each species in each time period, ultimately revealing a drastic decline in the abundance of grassland birds across the Nilgiris.

Access to archives

These and other scientists have also used different archival materials such as journals, old papers, and maps to complete unfinished stories of biodiversity collapse. In the study from Nilgiris, for example, the researchers used the first land-cover map of the Nilgiris, made by Captain John Ouchterlony, a British Officer stationed in Madras. This map was stored as multiple tiles at the British Library and the Tamil Nadu State archives. Using GIS and editing software, the team photographed the map, spent hours labelling the manner of land use at each pixel, and finally digitised it. Then they compared the information in the map with recent satellite images to assess changes and loss of habitat.

This said, accessing samples and archival resources in museums remains a complicated task.

According to Dey, “Key challenges include lack of digitisation, limited funding, outdated infrastructure, and bureaucratic hurdles in accessing collections.”

Most of the better natural history museums are in Western countries and accessing them is further limited by high travel costs and visa norms.

“​​The museum community has a problematic view of ownership of specimens,” Sushma Reddy, an associate professor and curator of birds at the Bell Museum of Natural History at the University of Minnesota, said. “For example, there are many specimens legally collected from India and other countries over the past century that are housed in these collections. What is the responsibility of these museums to repatriate information or allow access?

“[That is] something we are still struggling with as a museum community.”

Sutirtha Lahiri is a doctoral student in conservation science at the University of Minnesota.

Published – September 03, 2025 05:30 am IST