I'm not blown away by the importance of the Dutch case (and the sources aren't perfect). Perhaps it could be rephrased as simply something like "Vagrants have been seen outside of Cape Verde, having flown on to passing ships." This would also avoid the short paragraph.
Check the Alexander source- is the author's name Boyd Alexander, or Alexander Boyd? Also, what's going on with the issue number?
It's Boyd Alexander; the article is from series 7, volume 4, and the issue number isn't given in the citation. —innotata