Birdwatchers and conservationists in dozens of countries will mark World Migratory Bird Day on the weekend of 10-11 May 2008 with concerts, films and other public events to draw attention to the rising threat to migratory birds and global biodiversity.

The events will be focussing on one of the world's most magnificent natural phenomena - bird migration and the birds' journeys of thousands of miles between their breeding and wintering grounds. However, the global celebrations are being overshadowed by a series of recent reports indicating that the numbers of migratory birds are declining globally.

The decline in numbers is currently being recorded for many of the migratory bird species along all of the world's major flyways - the main migration systems, or corridors, used by various groups of migratory birds in different parts of the world.

For example: 41% of the 522 migratory waterbird populations on the African-Eurasian Flyways are declining and there are reports that numbers of migratory songbirds using the same flyways are also decreasing. A study carried out in Australia shows that populations of 36 species of migratory shorebirds travelling along the East Asian - Australasian Flyway have plummeted by up to 75% over the last 25 years. At the same time Boreal birds in the Western Hemisphere, like the Canadian Warbler, which migrate from the northern tip of Canada to South America are declining due to the loss of their forest breeding grounds.

While the exact reasons for the global declines are complex and vary from species to species and from flyway to flyway, the overall decline in bird numbers may be signalling a wider environmental problem linked to the loss of habitats and biodiversity worldwide.

Migratory birds and in particular long distance migrants are very vulnerable to environmental changes. To complete their annual migrations, they require breeding and wintering areas but also a network of stop-over sites along their flyways where they can rest and refuel before continuing on their journeys. Yet these important natural habitats and sites, which also host numerous other threatened species of plants and animals, are increasingly being lost globally with agricultural, urban, infrastructural and industrial development. For migratory birds, this means fewer sites are left for them to use throughout their migration cycle and that the network of sites they depend on to complete their annual journeys is getting thinner.

The loss and fragmentation of essential habitats is being further compounded by the effects of climate change: rising global temperatures lead to expanding deserts and more frequent storms which impact bird migration and subsequent sea-level rise threaten tidal and wetland areas which are important for many migratory birds ? all factors scientists are also linking to their decline.

Both the theme and the timing of this year's World Migratory Bird Day coincide with the forthcoming 9th Conference of the Parties of the Convention on Biological Diversity (CBD) to be held in Bonn, Germany later this month. In this context, the message of this year's World Migratory Bird Day is a clear signal to world leaders that more needs to be done to halt the loss of biodiversity and to increase national and international efforts to protect the network of sites required by migratory birds. Protecting these important sites for birds will be beneficial for other biodiversity as well.