If they were persuaded to put the food on a bird table, that might encourage the smaller birds and discourage the seagulls, as large birds find it very hard to get up on to bird tables and have to peck around underneath for the bits that fall off. Why don’t you treat your neighbour to a bird table - they aren’t very expensive and say that, as he got so much pleasure from feeding the birds, you thought he would like a nice bird table as it would attract different kinds of birds. We live just outside Oxford, which is about as far from the sea as you can get in this country, but if I put any bread for the birds on the garage roof, sometimes the seagulls appear from nowhere and the smaller birds are terrified of them. I know seagulls have to live, but not at the expense of our local garden birds!