Petrels are the most aerial and oceanic of birds, but, in the quiet sounds of Tierra del Fuego, the Puffinuria berardi, in its general habits, in its astonishing power of diving, in its manner of swimming and of flying when made to take flight, would be mistaken by any one for an auk or a grebe; nevertheless, it is essentially a petrel, but with many parts of its organisation profoundly modified in relation to its new habits of life; whereas the woodpecker of La Plata has had its structure only slightly modified.
Ekaitz-txoriak txoririk airetar eta itsastarrenak dira, baina Suaren Lurraldeko badia bareetan Puffinuria berardia, dituen aztura orokorretan, must egiteko ahalmen harrigarrian, igeri egiteko moduan eta hegaz egitekoan ere, hegaz eragiten zaionean, edonork hartuko luke, erraturik, pinguinotzat edo murgiltzat, eta hala ere ekaitz-txori mota bat da, baina bere organismoko atal asko sakonki eraldatuak dituena bere bizi-aztura berriekiko erlazioan; La Platako okilaren egitura, ostera, eraldaketa arinak besterik izan ez duena da.