It all makes sense now

Research on birds has shown that female canaries are more devoted to their young when they hear Al Green -- er, a "sexy" male serenade prior to reproduction:

Researchers discovered that certain phrases in a canary's song are "sexier" than other syllables. ... When the researchers played female canaries a recording of males singing sexy syllables, the females laid significantly larger eggs than birds that heard recordings of normal songs. "It may be that this is a difficult kind of vocal gymnastics to achieve; it may be that males who do this are in very good condition," said Roderick Suthers, a biologist at Indiana University who studies avian song production. "Maybe the female canaries pay attention to this particular kind of syllable because it tells them something about male quality—if these syllables are more difficult to produce, only the most competent males could produce them."

This, folks, is why songbird Britney Spears is such a negligent mother to the spawn of Kevin Federline -- no competent male would have produced a song like "Popozao."