Shanel Whiteford, of South New Brighton Primary School, asks :-

How many different kinds of birds use a large estuary?

Andrew Crossland, an ornothologist consultant, responded.

The total number of bird species recorded on the Avon estuary in Christchurch is 115, about one third of all bird species known to occur in New Zealand.

They weren't all seen at the same time. Some of them, for example Pied Stilts and White Faced Herons, live there year round but most of the others visit for only part of the year. For example, Canada Geese and Paradise Ducks nest in mountain valleys and lakes during spring but in autumn and winter these places are too cold for them (the lakes often freeze over with ice) so they come to the estuary where it is warmer and there is always plenty of food.

Other birds migrate here from almost as far away as the North Pole. The most famous of these is the Godwit which arrives at the estuary in September and leaves in March. You can see them resting at high tide on a sand island near the Spit tip.

Some of the birds recorded on the estuary have only been seen once or just a few times. Some of these are birds which migrate too far and forget to stop in warmer areas like South-East Asia or the Pacific Islands. Others are Australian birds which sometimes get caught in strong winds and find themselves blown across the Tasman Sea to New Zealand and the estuary. The Christchurch City Council published a very useful book called "The Estuary, where our rivers meet the sea" which has a lot of useful information on the birds which live on the estuary.