Longest bird penis

Argentine lake duck sporting a 42.5cm penis. Credit: Kevin G. McCracken et al (Source)
The longest bird penis discovered belongs to the Argentine lake duck (Oxyura vittata), measured at around 42.5cm, an astonishing dimension matches the length of an adult male, and compares to the length of an ostrich penis. If the Argentine lake duck were human, we could boast 5 - 6-foot penises!
It is not known why the duck has such a long penis, or even how it is used during mating; the penis is also covered with spines, though the tip is soft and brush-like. it is noted that the duck is promiscuous and boisterous in its sexual activity.
Notes:
- Kevin G. McCracken, Robert E. Wilson, Pamela J. McCracken, Kevin P. Johnson, "Are ducks impressed by drakes’ display?", Nature, Vol.413, 13 Sep 2001, page 128. (Full text, PDF)
- "Friday Weird Sex Blogging - The Birds Do It....", ScienceBlogs, July 14, 2006
- "Found! The longest bird penis ever", ABC News in Science, Friday, 14 September 2001