Our Schnapsdrossel (WoM for March) needs a drinking companion, and here he is. A Schluck is a gulp or swig (from schlucken - "to swallow"), and a Specht is a woodpecker. Put the two together and you have another moniker for a boozer or drunk. Again, I do not know how the word originatedperhaps the alliteration of the two components (the S in Specht is pronounced like English "sh") played a role.
Addendum (4/9/2012): According to this theory, the term goes back to certain woodpecker species that hammer holes into tree trunks in order to get to the sap.
Anyway, we have a word that may look daunting to foreigners: 11 consonants and only 2 vowels! Things appear easier when you realize that the "sch", "ck", and "ch" indicate but one phoneme each, which reduces the number of effective consonants in the word to 7. Still, for speakers of languages that avoid consonant clusters (like Japanese) the word is a challenge.
[Source: Wild Things in the German Language: Kindle version | iBook version]