H4RDY; Welcome to WPF.
I am completely agree with Don, Duncan and Greypoint.
If novice, you would actually like to do the reverse, i.e. get experience with DSLR and once becoming expert in technique then switch to EXPENSIVE film cameras. Frankly I would not think anyone does that switch once you get used to convenience and speed in having final image result with DSLR as opposed to film ones.
But to answer your question. For bird photography, 400-500mm range is a must. With unique contex/yashica mount and interest in digital cameras these days, you should be able to pick up some decent ones with decent price as a used lens. Check ebay, MF or likewise.
I suggest Quantarary lens 600-1200mm zoom, that uses a T mount which via appropriate adapter fits into any camera, probably you would be able to use it on your future DSLR. I got one of these now being used on my canon DSLRs for about $130. Glass on this is decent and price even better. There is another version of similar lens that comes as 500 with a 2x extender that I saw one on ebay in 25 sec search for yashica.
L I N K .
I am not sure of glass quality on this but should be what you are paying for.
No mater what please do not spend much because film is really too cumbersome, expensive and you will switch soon for sure. I look at film cameras only as collection items that I hold very dear especially the Nikon line or for real work only as nightmare.
On the bright side, if I am correct and pretty much I think I am right that this Yashica was the first AF SLR that introduced a manual function for "Prefocused zone shoot" that on manual you pre select a zone (By manual focusing), leave camera on and on a tripod and once a subject enters that zone, it takes a picture. Good for bird shooting if you know where but not when to expect that unexpected visitor or a surveillance function that is good for example checking who uses your office, specific room etc. I am yet to see this feature on any other camera, Of course you can always hook up an electronic trigger attached to some remote shutter release but this one is the least hassle version.
If by any chance you changed your mind and have inclination to go for DSLR, then please put up a new forum so that we may be of help or just search existing forums an you may find enough suggestions.