The series 3 systematics are much bigger than your regular tripod. They also stand very tall without a center column, so that means the leg spread will be more than you likely are accustomed to.
The GT3530LS has a folded size of 26.4" / 67cm (no head). That might be too big for your travel bags, you should make sure it will fit in your suitcase. It will be about 5.5" - 6" diameter at the top plate.
I use the GT3541LS for photography. Same tripod (within an 1" or so of max height), but with 4-section legs instead of 3-section. It has a folded size of 21.7" / 55cm, which is still very big compared to the smaller travel tripods.
I think the current version is the GT3543LS or GT3533LS.
I think the series 3 systematic is great for super heavy loads or where you need to weigh it down and dampen vibrations. No center column helps a lot too. But I think for on-the-go bird watching, especially if backpacking in gear or trying to fly with it, the series 3 systematic is going to be a major piece of kit. Too much, I would say. Try to see one in a store, they really are much bulkier than your normal tripod.
If hiking with the tripod, you will need a more serious backpack and use the waist and sternum straps. The systematic will be top heavy and tend to twist or pull the pack at your shoulders unless balanced well. You might also need to remove the head as that will torque it even more, which means even slower setup. With head, it will be a 24"-26" (more or less) conic section that is 3" - 6" diameter and top heavy. Think about how you would strap that to your pack. I have the WH-200 gimbal, so mine is super top heavy -- maybe I am making too much of this.
You should also consider what head you put on. Having a system 3 systematic with a Sirui VA-5 is missing the point. That head is not built like that tripod. Get the 500AH or 502AH to go with a systematic. The VA-5 is better suited to the series 1 or 2 traveler or mountaineer.
You should figure out what will fit in your bags and how tall you need it to be and work backwards from there. You should also decide how sturdy you really need it to be. If it's your job to go out in all conditions and make observations, sure get a bigger tripod. If its a hobby and you need to hike in with the thing or pack it for air travel, I'd consider a series 1 or series 2 as others have suggested.