That seems like a long way to have come in a month!
I've offered a couple of suggestions, mentioned stuff that seems odd to me, and my own attempts at the lines. I wouldn't claim to be a expert, but hopefully it's not completely off.
SOMETHING POSITIVE
By R.K.Milholland
I think with titles, you can get away with just leaving them in English (or putting them into katakana). It seems to be the usual practice nowadays. Also, you can leave initials as letters. The の at the front of the name seems misplaced as well.
SOMETHING POSITIVE
著:R・K・ミルホランド
Damn it! That's another tomato that bird's ruined!
"破壊した" seems a bit dramatic for a tomato, to me.
クソ! あの鳥だ、またトマトを台無しにしたんだ
Well, look who's back? Here to gloat or eat more of my fruits and veggies? I bust my ass for this garden, you airborn duster.
I think "自慢" would be more boasting about something (like how great your new car is or how successful your children are, that kind of thing), rather than the bird gloating over having eaten the guy's tomatoes. "自慢したくて、野菜を食べたいの?" seems a bit unclear to me.
ほう、のこのこ戻ってきたな。ほそく笑みに来たか、それともまた食べたくなったのか?
僕は本当に苦労しているんだよ、この鳥ヤロウ
I sweat and you watch. I work and you don't help but when the fruits of my labor come up, who's the first to swoop in and gobble up what he's got no right to?!
There's a name for the likes of you.
I think you need to use more particles (like 僕が汗..., rather than just 僕汗). Also, 君 seems a bit too soft to use towards a bird who's been messing up your garden.
僕が汗水たらして働き、そしてお前はただ座視する。
僕が労働する、しかしお前は手伝ってくれない。
手伝わないくせにいつも成果が実るとお前が先にいただきだ!
お前のごときには(ちゃんと)名前があるんだ
So, why did you name the bird "I.R.S."?
I think it could do with an explaination/the Japanese name of the IRS there for anyone who doesn't know. You could still keep "IRS" as furigana over it thought (I don't know if there's a good way to produce it on a computer, except writing it seperately and trying to place it above the text).
じゃあ、なんで(鳥を)「国内国歳入庁(I.R.S.)」と名付けたの?