i'd strongly disagree with not giving birds vitamins most feeds are lacking vitamins and can differ from crop to crop hence the need to supliment vitamins , now you say 'Blackberrys and Elderberrys in our case ' surely these contain vitamins ? birds forage in the wild and readly eat berry such as hawthorn and elderberys but when there in season and keep themselves right , rember our birds arent wild but still have the same dietry needs and we need to suply them , if not more so when we force there migratory instincts to race and the strain this has on them.