Now, in the bird books it tells you that the crown colour of Goldcrests helps with identification but in the field it is very difficult most of the time to tell the difference between the sexes.
Females have a wholly yellow central crown and male have yellow with firey orange in the middle. However, as you will see in these two shots from Brenda it does not always show up unless the male bird is exceptionally excited! At this point it expands out from the middle so that pure yellow becomes a blaze with an orange centre! I would imagine that this surprise change in colour has even more of an effect on rival males or passing females!
Ooooh! this one must be a female!
Want to be on that!