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        Discussion Area 討論區 >> General 一般問題 >>  Migratory Bird Day celebrates colonial birds
        
(Message started by: Project Officer on May 14^th, 2004, 2:39pm)

Title: Migratory Bird Day celebrates colonial birds
Post by Project Officer on May 14^th, 2004, 2:39pm

An interesting piece of information from BirdLife International, share with you.

Quote"

Migratory Bird Day celebrates colonial birds
07-05-2004

Communal nesting behavior is being celebrated in the 2004 International Migratory Bird Day (IMBD), being held across the Americas on 8 May.

Nesting in colonies has been a successful strategy evolutionarily for 1 in 8 species of bird worldwide. Many communally-nesting species are water birds, such as frigatebirds, herons, egrets, gulls, terns, and puffins, but several landbirds such as swallows and blackbirds are also colonial. Colony sites take many forms: mud nests plastered on vertical surfaces; burrows riddling a seaside cliff, a stretch of depressions in a sandy beach, or bulky stick nests forming a woodland rookery; what defines them is the close proximity and social behavior of the colony members.

Why do birds gather together to nest? It is believed that coloniality evolved in response to shortages in suitable, safe nesting sites within range of food sources. Birds nesting in colonies may enjoy safety in numbers, for example, when colony members cooperate to chase off predators. Congregatory nesting behavior does have disadvantages though: colonies may actually attract predators, foster higher rates of disease or parasitism, and members may experience increased competition for nest materials and food.

Coloniality also increases population risks by concentrating birds in a limited area. In other words, a single event or incident can affect the nesting success of a large number of birds. There have always been natural threats to colonies such as storms and predators, but human activities have brought many new threats to colonies. The introduction of exotic species to breeding areas, disturbance of colonies, and outright loss of breeding habitat threaten many species of colonial birds.

Fortunately, colonial birds and their colonies are often highly visible and impressive, and thus can garner positive public attention and support. IMBD 2004 will be a chance to celebrate some of the most impressive bird sights in the world.

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