I tried looking online but I couldn't find anything. Is it possible to train this behavior out of a budgie or is it just something you have to deal with?
I have two budgies - one female and one I thought was female until a few months ago but is probably a male - that have been together for 2-3 years. The problem is that the younger female is always picking on her cage-mate. I know females are rather aggressive, but I feel bad for my male. It's mostly noticeable when it comes to food.
I'm trying to tame them right now and so I use both millet, kale/lettuce, and seeds. The female always tries to hoard the food to herself. She's always getting in his way, pecking him away, restricting his access to the food, etc.
Do they have two food bowls (and two of everything else in the cage, too)? Oftentimes, one bird can get possessive over what they see as "their" food bowl.
If it gets to the point where she doesn't ever let him eat at all, you may have to separate them for mealtime or just house them separately (you can still keep their cages next to each other if it doesn't stress them out).
and Princess Mallorn!
Thank you to Deb for her wonderful Faery magic
You indicate the younger female is "always" picking on her cage mate. If that is indeed the case, then it isn't a good idea to house them together. They would be better off to be housed in individual cages and only allowed to have supervised out-of-cage time together. The budgie that is being continually bullied will suffer both emotionally and physically if you allow it to continue.