Please advise on best choice of pellets for my Air Rifle

Hello, I am new to airgunning, and bought a rifle to shoot sparrows at my purple martin colony. Shooting at about 30 - 40 yards max. I only need to shoot sparrows, nothing larger. I have a RWS 34 Diana rifle, with a Hawke Vantage 3-9 x 40 AO Mil Dot IR scope.

Please advise me on what the best pellet is for accuracy , sparrows being a small target, at least for someone without much experience with rifles.

thank you very much for your help, Peter