Marking World Migratory Bird Day, the agency said that the decline is being recorded for many species along all of the main migration corridors, which birds utilize on their journeys, spanning thousands of miles, between their breeding and wintering grounds.
“Migratory birds are some of the most extraordinary creatures on the planet and in many countries bird watching is an economically important leisure and tourism activity,” said UNEP Executive Director Achim Steiner.
“But migratory birds are more than this. Their dependence on healthy habitats and ecosystems makes them among the key indicators as to whether the international community is truly addressing the decline and erosion of the planet’s nature-based assets.”
The Day – focusing on the theme “Migratory Birds – Ambassadors for Biodiversity” – will be marked on the weekend of 10-11 May with concerts, films and other public events to highlight the ever-increasing threat to migratory birds and to global biodiversity.
Although the reasons behind the drop in numbers of migratory birds are complex and are specific to certain species, the overall decline is a reflection of the larger environmental problem tied to the global loss of habitats and biodiversity.
UNEP noted that 41 per cent of the 522 migratory waterbird populations on the routes linking Africa and Eurasia are witnessing their populations drop, and it has been reported that numbers of migratory songbirds using the same corridors are also on the decline.
Meanwhile, numbers of Boreal birds in the Western Hemisphere, such as the Canadian Warbler, which migrate from northern Canada to South America, are plummeting because they are losing their forest breeding grounds.
Vulnerable to changes in the environment, migratory birds are dependent on stop-over sites to rest and refuel as they make their long voyages, but these locations are threatened or disappear as a result of agricultural, urban, infrastructural and industrial development.
Climate change also plays an important role, as climbing global temperatures result in larger deserts and more frequent storms, which could lead to rising sea levels and impede migration.