Sudden death of Toulouse Goose?

Last night I heard our geese honking like crazy, which they never do unless something is up, and when my wife and I checked on them six of them were standing around one who was lying down with her wings splayed out symmetrically and her head back over one side of her wing. It looked like a peaceful repose. We think she just died, naturally. There was no sign of anything else. It was quite sad to watch the other geese, after honking loudly together, to just kind of sniff her and then slowly walk away.
They were in a certain pasture temporarily to offer them some fresher feed. There has been NOTHING about her recently to indicate anything was wrong.
Has anyone else experienced anything similar to this? I'm not really concerned, just curious.

Hi Brett, when you say in "a new pasture" that sends out warning signals to me that there may be something in there which caused her death - especially since there were no outwards signs of a struggle or injury.

Do you have any Portulaca (Also called Pig weed, Purslane, Pusley, Sun Plant, Verdolaga etc) growing in that pasture ? If you have get them out of there as soon as possible or you'll lose the others too.

Purslane irritates their digestive tract and kills geese if they eat too much. I'll see if I can find a reference to this in the 'net somewhere. 

Irene

Thanks for the response Irene.
I should qualify my statement by saying it is not a "new" pasture as it was a newly rotated to pasture they had been in before. We have portulaca in our "front yard", I guess our Zone 1 area, but they do not have access to it.
I considered if it was a plant toxin issue, but I kind of don't think it was considering the geese, chickens, and sheep have been in that pasture plenty of times. I know it still could be a plant problem. That pasture butts up to our "front yard" but is separated by a fence and the portulaca is nowhere near that area.

OK Brett, sorry to rush in like that but the problem in a forum is that we don't always know the level of knowledge or experience of people who post.

Do the geese have access to water ? You probably know that big birds like Toulouse geese can't mate easily without it. (Sorry if I'm teaching you to suck eggs here.) Could she have been injured by a male whilst he was trying to mate with her on dry land ?

No worries Irene,
They did have access to a child's pool. But there was absolutely NO indication of any kind or trauma. The feathers were intact and she was just laying there like someone laid her out peacefully.
From the, admittedly, little I know of Toulouse Geese is that they don't need to have ponds, but I didn't know that they mated in water. These are not the big dewlap ones, but they are still big. They are new to us, which is why I am asking the questions. I don't mind if you keep asking what may seem like obvious questions, because I surely don't know.

too late now,,,but an autopsy may show you a thing or two.  enlarged heart.  bad liver,  hemoraging of some sort, etc. 

sometimes animals just die,  like humans, but we sometimes never know something is ailing them.  ive butchered many animals and seen organs that werent right.  you would never know it, by their daily demeanor,  but it was just a matter of time and they would have died a worse death with more suffereing.