Migration: lost birds

On March 18th, an unidentified small bird took refuge on the Sail Training Ship Lord Nelson, about 400miles north od Tenerife, and 200 miles west of Gibraltar.  A persistent North-East wind blew for most of that week, about 20-30knots.  The bird (photo attached) was very small, about the size and shape of a warbler.

It was very tame and perched on crew heads and hands.  After two days, 200 miles further north, it flew off.

What was it?         We also had a lost swallow, which took refuge in the charthouse for three days from about March 20th.  Photo attached.   I saw swallows in Gran Canaria from March 7th.