a - head; COTE - crown: front white and back black (or crown partially peppered ); forehead white; nape part of cap black; FOTE - black ‘bandit mask’, crown and forehead whitish to blackish (peppered), nape part of cap grayish to peppered, not solid black

b - ‘carpal bar’; COTE - YES (well defined during this time of the year); FOTE - NO (but juvenile FOTE can show pale carpal bar)

c - primary molt; COTE adult inner primaries new, outer primaries old (in the middle of primary molt); COTE (adult) completed or about to finish with outermost primaries shed or growing (also check illustration of roosting terns: juvenile FOTE has all dark juvenile primaries)

d - outer web of outer rectrix (R6); COTE - BLACK; FOTE - WHITE

e - rump; COTE - GRAY; FOTE - WHITE (best visible in poor light)

f - white tongue pattern and length in outermost primaries (see illustration); helps to separate Common from Arctic (longer white tongue) and especially Roseate Tern which has white tongue extended to near the tip of primary.

I did not include description of few traits sometimes included in guides. Different shape of heads, bill and mask black area extended in front of the eye - those traits I found not easy to be verified, especially in the field, ; ventral body parts coloration (grayish in COTE and white in FOTE) is not showing differences during November (it is found in ‘summer’ plumage‘ - this I will illustrate in different sets) - in both species is white in November.