Problem with Continuous Shooting

I have recently noticed that when my T1i is in Continuous Shooting mode, I can only take three or four shots, then the camera stays 'busy' for over a minute. I have to wait for the 'busy' light to go out and the 'number of shots left' to stop flashing before I can take any more. This is not a problem with landscapes, etc. but it's playing havoc with my nerves when I'm shooting birds. Does anyone here have a solution or can give some idea of what may be wrong?
Reset all personal functions
High ISO Noise Reduction set to 0
AF set to 'AI Focus'
Thanks.

The buffer is full. If the time to clear the buffer is unusually long for this camera, then that suggests that you are getting a very slow write speed to the card. There could be an issue with the card, or you could have a very slow card.

Keep in mind that all cameras will fill the buffer faster than they can clear it. After I rattle off 30 shots on even the 1D Mark IV I will be stuck staring at that red busy light for a while too.

First thing to check I suppose would be what kind of card you are using. Then see if a different or faster card helps.

Yeah it sounds like your card isn't fast enough... you can pick up Sandisk class 10 cards very cheap these days.

Don't go and buy the best one money can buy at 90MB/s or whatever, because the T1i doesn't support uhs-1... 20-30MB/s should do the trick no problem.

Having said all of that, buying a new card won't allow you to rattle off hundreds of images in one go, because you will still fill the buffer quicker than it can write to the card... you will probably be able to get 6/7 away in full-speed continuous before it slows to about 1.5/2 fps after that

also, are you shooting RAW? If you are then you'll be limited because of the larger filesize. I'm guessing you'll be able to shoot 6-7 until the burst fills, but if you get a faster card, then you won't have to wait as long for it to clear. RAW + L jpeg would be worse (in terms of number of shots before the buffer fills)

If you shoot just large jpeg, you may be able to get away with an almost infinite burst. At least that how it is on my camera...I don't remember what the manual/reviews claim for the t1i. But if it can write 20-30 MB/s, then you don't have to worry about the buffer because it'll write to the card faster than it can fill it.

Also, you probably don't need to use AI Focus. Most people here, ignore AI Focus. Just stick to One-shot or AI Servo (in this case, you'll want to use servo, since you're tracking birds).

The other thing not mentioned so far would be to do an in-camera low level format of the card (after removing all images). Doing a format in a card reader, or just "removing images) has been known to cause the write process to slow down. Doing this is especially justified if you feel that performance of the camera/card has suddenly changed.

Personally I never chose erase images but just do in-camera the low level format.

Thank you all for your suggestions. I have been using the same card for some time, so I'm not that's the problem. However, I did recently switch to shooting RAW + Jpeg, so that is probably why I'm suddenly seeing a slow down in Continuous Shooting. I will just have to learn some patience..... :/

I also format the card in camera once I have downloaded the images on it.

Therin lies the problem. Your camera is a busy feller when it is trying to write all of that data.

You can test it by shooting a test burst in jpg only, then try RAW only.
I use Transcend 400x cards and have for a couple of years. The 32 gb card seems to transfer faster to my hard drive via USB 3 card reader than the 16 gb cards. Not sure why but it does.

Note: The few times I shot RAW + jpg, I also had the buffer fill a few times on the MK III. 'Course I was shooting outdoor sports and the action was fast. Only reason I did that was so I could turn the jpgs over to my webmaster for quick display on the web while retaining the RAW for tweaking after sales orders come in. Otherwise, I shoot RAW mostly all of the time.