There was a thread on the old 1965 Thunderbird tokens last week. Here is a comparison of the two varieties for those who haven't seen them both. Note that on the 'no birds' variety, the birds are missing from the obverse, but still faintly present on the reverse. Both types are dated 1965.

These copper tokens have an incuse design unlike the great majority of later gaming tokens. That means the birds would have been raised on the stamping dies. My theory is that they either wore rapidly and disappeared or they broke off the die in later strikes. It's also possible that there was a separate die made for the obverse, possibly to a die breakage while stamping, and the replacement didn't get the 4 birds added.

Both tokens shown are the same copper material but the lower one has significant toning. The upper one either has some wear, or a previous owner has polished it. The Michigan Tool Engineering tokens are often seen with this shiny, untoned surface.

Janice O'Neal's catalog lists these as Type I-No Birds, catalog 459, and Type II-With Birds, catalog 460. Type I seems to be much scarcer and I believe it's the toughest of the 8 copper TME tokens.