Thanks for your experience. I believe next door's birds are well looked after so hopefully that isn't the issue. Unfortunately I wasn't home at the time of his visiting next door, my husband dealt with it. I only heard about the incident when he was sick the second time. My husband knew he'd been eating something and had checked with the neigbours (who had helped him get hold of our dog, who is now deaf due to old age) that they hadn't put anything down. I'm hoping it's just that his body didn't like all the seeds. Time will tell I suppose but I can't make up my mind whether I should contact the vet.