Garça, gaibéu, Al-Jaziira, Algeria

As some of you may know, I'm very fond of the song Garça perdida by Dulce Pontes (track 7 of O primeiro canto. I must have looked up the word a few times, but I could never remember what it meant, because nome vulgar extensivo a umas pernaltas da família dos Ardeídeos didn’t mean much to me. I didn’t know the English word heron either, which was in the translation in the cd booklet. OK, so now I know, we call them reigers. I often see one (they're solitary animals), they learned how to live in city parks, and even in Amsterdam canals (grachten) or so I heard.

The Portuguese word garça, says the Porto Editora is from Latin ardea (ardĕa, if you can see an e breve). Now this is a rather unusual difference, usually Portuguese word are much closer to their Latin ancestors. Are any intermediate stages known, to see the development from ardea to garça?

Probably while looking up garça, I can't exactly remember, I came across the rather strange looking word gaibéu. It means:
Jornaleiro da província portuguesa do Ribatejo ou da Beira Baixa que vai trabalhar nas lezírias durante as mondas.