New clues about the mysterious decline of shorebirds

According to recent reports from organizations such as BirdLife International, more than half of all shorebird populations are currently in a state of decline. Despite being a global phenomenon, the driving factors behind the dwindling numbers of sandpipers, plovers, avocets, oystercatchers, and other shorebirds remain unidentified.

In a new study, researchers at the University of Lisbon have pinpointed environmental changes that may help to explain why shorebirds are vanishing.

“Shorebird declines are occurring worldwide but the causes are not fully understood,” wrote the study authors. “Recent literature suggests that the deterioration of habitat quality at their non-breeding areas, mostly located in temperate and tropical coastal wetlands, might be a major contributing factor. However, most studies carried out so far tend to be restricted to a few regions.”

“Remote sensing can help correct such geographical bias on knowledge by providing a standardized approach on how shorebird habitats have been changing over the last few decades at a global scale.”

The team used remote sensing data to analyze habitat changes in 907 sites – known as Important Bird and Biodiversity Areas (IBAs) – over the last two decades. The researchers were especially focused on changes in low tide feeding areas and high tide roosting areas. 

“Globally, supratidal areas (used as roosting habitat) have changed more significantly than tidal flats (used as feeding habitat). Yet, we found striking losses of tidal flats in IBAs distributed in several regions of the East Asian – Australasian Flyway,” wrote the researchers.

“At supratidal areas, there was a general expansion of marshland, grassland and urban areas, contrasting with a decline of barren land, woodland and cropland. The expansion of marshland occurred in IBAs of most regions of the world. Urban areas also expanded consistently in supratidal areas within the most populated regions of the world.”

The experts noted that the loss of barren land is particularly concerning as it may translate into a loss of high-quality roosts. According to the study, changes may be urgently needed to save some species of the East Asian – Australasian Flyway that are facing population collapses due to habitat loss.

“This global approach is a step forward to understand the causes of shorebird declines, a group of birds that is already threatened,” said study lead author Carlos David Santos. “Many species of this group are long-distance migrants, some moving more than 20.000 km annually, thus they can be affected by environmental changes occurring at different regions of the world – this is why a global analysis of such changes was so important.”

The research was a collaboration between experts from the Centre for Environmental and Marine Studies (CESAM) and the Centre for Ecology, Evolution and Environmental Changes (cE3c) at Ciências ULisboa.

The study is published in the journal Science of The Total Environment.

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By Chrissy Sexton, Earth.com Editor

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