bearfoil;
Meantime, and without the "Bird", a pilot has no heading (crab) reference,
Not quite...the PFD and the ND have a full-time (green diamond) "track" symbol on the compasses so that the pilot can compare track with heading (blue triangle) and thus derive drift. Also, there is a full-time wind symbol on the ND, top-left.
Clearly, (when not in NAV mode), in HDG/VS mode the Heading/Track symbol overlays the heading, (yellow lubber line at the top of the ND) and in TRK/FPA mode the Heading/Track symbol overlays the green diamond track symbol and lines up with the green track line, (4th graphic in HDG-VS, 5th in TRK-FPA). One can see the drift in either mode or even if the FD's are off as in this case. In NAV mode, the Heading/Track symbol is removed.
The presentation is visible at all times no matter what mode the FD is in, even if it's off. The bottom graphic shows the relationship between the Bird and the Track.
Here are three graphics which illustrate the symbols:
Hope this helps. Thanks for your note on the other thread.
PJ2