Hi Kenny, (Scrub),
For the types of stamps you have mentioned, the colour trials, proofs etc, I have never known how to value them myself, even from Canada. Probably out of my price range anyway.
Auction catalogs, checking some online dealers (not necessarily
ebay, etc), for France and territories Yvert et Tellier is the specialized catalogue you want but I am not sure if they have those types in their catalogue.
http://www.yvert.com/ (web site in English)
but keep in mind, other country's catalogues usually have different numbering systems that Scott's catalogues (better for USA).
Birds are a popular topic or theme of collectors. Very beautiful usually. People pat more for beautiful items so your mom chose wisely! More people bidding and wanting, the price goes up.
Some of the prices you have probably seen for the colour trials and proofs and imperfs are due to this popularity factor and dealers and sellers trying to take advantage of the impulse buyer. If you are collecting you can chose to be patient and diligent and mount the hunt and keep you eyes open for the deal. Works for a lot of people although I am myself prone to the impulse buy now and then.
Remember to search the collector site Delcampe (.com or .net for worldwide) for some items at more realistic prices (sometimes).
Stanley Gibbons (Catalogue maker and stamp dealer in Great Britain) has some topical catalogues available, or you may find them online somewhere.
ANTARCTICA & TERRITORIES 1ST ED
COLLECT AUTOGRAPHS CATALOGUE 2010
COLLECT BIRDS ON STAMPS 5TH EDITION--2003
http://www.stanleygibbons.com/online-shop/Sometimes topical dealers online (google topical stamps) have the item.
Check the local stamp club or stamp shows too. Watch what happens and see how others do it. Shows have nice contest displays also usually. at least here they do.
Put you other questions in any language that Google can translate incorrectly

and I or other more international members can have a go at it. Or, if you mean English but you don't know the proper words then just ask anyway and we will figure it out. I have been doing this stuff for years and I still don't know proper words.