Did you find out what had caused it? I live in Egypt and have lost 7 ducklings and 6 goslings over the past few days in the same way. I thought it might be botulism, the heat, lack of water, except that they have loads always, or something they had eaten, I am at a loss and vets here are not particularly efficient!!! The chickens however are fine. A couple of deaths as the temperatures have suddenly shot up to 46 degrees Celsius, so very hot. Too hot for my Irish blood that's for sure!! But if it something in the soil here, which I strongly suspect, I won't be buying any more waterfowl until we have our own place and can be sure of what they are eating.
Its hard going losing so many birds as I love them, so I completely get where you are with your birds, But do let us know what the vet says and hopefully it will help many others too. It seems to be such a common thing and yet no-one knows what seems to be causing it. I've done loads of research and come up with nothing!!!
Its heartbreaking really but I am glad that you still have Pear.