I agree with DAD's id of these birds, which is in line with how we identified at the time on the boat.
These and other shots taken that day are very informative with regard to combinations of features which help to separate what are often surprisingly similar species in autumn, either as juvenile/1st winter birds or as moulting adults.
The HY (hatching year) Aleutian Tern - it seemed there was just the one, which was attended by an adult - is I believe just the second such record for HK.
Mike Turnbull
