The black bib marking of the male gender
The male common
house sparrow has a black throat ("
bib"). It becomes most visible during winter and spring after the
moulding season of
autumn.
Males with larger bibs are preferred by females even though they are more likely to cheat on the females in an otherwise
monogamous relationship.
Researchers have shown that the males with larger bibs tend to have larger
testes (meaning larger
sperm count), and in
feathers less
ectoparasites and fewer
fault bars (a perpendicular line in feathers which indicates a period of stunted growth, sort of like a dent or white spots on peoples' nails). These
sparrows are more likely to
preen often to display their larger bib, which is another plus for health, while males with smaller bibs may not do so as frequently in order to avoid hazing. Females choose males with a larger bib to benefit a higher chance of
fertilization and a lower chance of catching parasites during
courtship.