Strange duck

Hi everyone,

What with one thing and another, I have taken to extending my morning dog walk into a mini-survey of our local Suffolk Wildlife Trust reserve. Luckily, they have been getting control of farmland around my house now for a few years and have added it to Spouse's Vale and Arger Fen, which is mainly mixed woodland. So I feel very lucky at this difficult time to have that as my daily outing.

What I am on here for is this: there are two ducks which roost up a tree. They flush and make a really loud repeating trumpet sound. The only ducks I have seen locally are mallards - and they aren't them - and a mandarin duck on a local pond the other morning.

Does anyone have any ideas about the mystery trumpeting tree ducks?