IT is all change at one of Suffolk's busiest nature reserves, where one bird has flown and another has landed.The tern has come to breed, while the bittern has taken off from the thriving marshes at Trimley.

IT is all change at one of Suffolk's busiest nature reserves, where one bird has flown and another has landed.

The tern has come to breed, while the bittern has taken off from the thriving marshes at Trimley.

Throughout the winter the foghorn call of the bittern – one of the rarest birds in the UK – has been booming across the wetland, the first to stay through the coldest of seasons for seven years.

Now it has flown – probably to Minsmere – for the breeding season. But twitchers have a new visitor to focus on – a colony of breeding common terns.

Organisers of the reserve, on the banks of the River Orwell, are hoping the bittern will return in a few months' time and bring some friends.

Warden Mick Wright said: "It was really good to have it on the reserve. Even though it is a very secretive bird, lots of people saw it.

"Our regular people down here got to know where it was standing during the day to feed and which part of the reeds to watch and got quite good views of it.

"We haven't seen it now for about three weeks so we can only assume that it has gone to its breeding ground, probably Minsmere.

"It was not the first bittern we have had here but it did stay the longest. They tend to come back to where they have been before, so we may see it again.

"We have good fish stocks here now and I think we have enough room on the Orwell for a flock of bittern."

The reserve – a man-made habitat built originally to compensate for the loss of other habitat when Felixstowe port expanded – has matured over the past decade and its reservoir and dykes now have large shoals of fish.

Its reed beds are 20 metres deep in places, shallow enough for waders, and offer good cover.

"It's all helping to attract birds and we are seeing a lot of visitors coming for the fish, especially cormorants and great crested grebes," said Mr Wright.

"We also have over 40 common terns – I expect that number to grow over the next few weeks – and all three of our tern rafts are being used."

While it attracts visitors all year round, the spring weather has also brought more visitors to the reserve to use its hides and visitor centre. Last weekend, a working party carried out a beach clean, removing large amounts of marine rubbish.

FACTFILE: Booming bitterns

n Described as a thickset heron with all-over bright, pale, buffy-brown plumage covered with dark streaks and bars, it flies on broad, rounded, bowed wings.

n Bitterns are secretive and difficult to see, living in reeds at water's edge, looking for fish. But they can certainly be heard with the far-carrying, booming voices.

n They spend the winter in freshwater marshes with reedbeds and other thick vegetation; also gravel pits, ditches and rivers.

n Suffolk's Minsmere reserve and Leighton Moss, in Lancashire, are the best places to see the birds, which are among Britain's rarest species

n They live on fish, amphibians and insects.

n The UK has 20 breeding pairs and around 50 to 100 wintering birds. Their lifespan is ten years.

Source: RSPB