Terns are they common?

[Bella]

I'm quite new to this so bear with me.  I'm sure terns and seagulls are not what most people are interested in (I think).  Here goes:

Are Caspian Terns common along Lake Huron?  I saw a pair of Terns (at least what I interpreted to be terns, def. not seagulls) on the weekend, but according to my info they are not that common there.  These two were very large, their wing span huge.  They had the black cap with a little tuft at the back of the black part and all red bills.

I also observed what I perceived to be a smaller Tern but I could not identify it with the info I had.  This one was quite a bit smaller than the average seagull, it has the notched tails feathers but was ALL white, in fact brilliantly white, with a black bill.  I aslo saw the same elsewhere but with a red bill and almost all white but def. had some grey.  Both were dive bombing for fish in Lake Huron .The first one I watched for hours on our little harbour the other was in a larger harbour.  Can anyone clarify this for me.  

thanks in advance, so far you have all been great!

[thouc]

Caspian Terns are fairly common in Lake Ontario so I guess they could be in Lake Huron too.

The grayish Tern with red bill is probably a Common Tern, also fairly common.

The brilliantly white with black bill is a bit more tricky, but I would guess Forster's Tern, which is quite rare (haven't seen it myself)
In it's breeding plumage it has a black cap (like Common and Caspian) and orange bill with black tip and it's wings are whiter than those of the Common Tern.
The winter and immature plumages are all white with black bill and only a black mask around the eye. Seems like wrong time of the year for those plumages though. Does anyone know if birds born last year could still have the immature plumage?

Regards,
 Thomas

[Bella]

Thanks so much for the response. That really helps.  I'm not sure how comprehensive my one and only field guide is so your information does help.

About the terns though, the all white one was just that, so no breeding plumage.  I got a good look at it and it had no grey or black.  It was my entertainment for hours, I hope it had a nest somewhere it was feeding, because one bird could not possibly eat that much fish, unless of course it was just really bad at catching them.