Best settings for capturing birds

Hey /photographyI have borrowed a 15 - 300 mm Tamron lens from my brother in law, while I save up for a 150-600 mm telezoom lens. I have tried a few shots at some birds but I find that some of my photos get blurry when capturing with the lens in hand. This "scares" me and I get intimidated to get a 600 mm lens since I get blurry pictures with a 300 mm.I try to understand the settings and so far I understand that quick shutter speed give less shaky pictures but does not allow for much light to enter the mirror. I think the blurry pictures are a mix of a too slow shutter-speed and perhaps too little sun light outside.I set ISO to as low as possible and that is about how much I know ATM.I am getting a tripod next week, but I feel like with bird pictures you cannot always just sit there with your tripod and wait.. sometimes you gotta "catch" the moment with your camera in hand.I use a Nikon D3400Any advice would be appreciated . via /r/photography https://ift.tt/2TEisBk