the figurative expression "calling card" is similar to "hallmark" meaning a recognizable element, behavior, etc. Both of these terms originated in physical items (literal calling cards, cards with your name engraved on them. They were used before the telephone when a person would drop by to visit, and the person was not at home) Hallmark was/is a mark on a gold bar. http://dictionary.reference.com/browse/calling+card?s=t http://dictionary.reference.com/browse/hallmark?s=t

1) A calling card is an old term for business card. So it is something that is used to identify someone. In this case, plunge diving is what identifies the gannet. 2) It does not refer to a "special chance." 3) It is not used very often in the US. Elderly people might use it when they ask for a business card, and it's definitely not used often in colloquial conversation.

Originally a 'Calling Card' was a card with a persons details left by someone who was unable to see the person they came to visit. Nowadays it's often used to describe an item left (for example in my garden 'hedgehog droppings' because I'm asleep when they are around) or a unique action made by animals or birds. In this case gannets. It can also be used to refer to a person but it's less common.

http://www.urbandictionary.com/define.php?term=Calling%20Card hope it helps

I have no idea what it means. Based on my best guess it would be a "featured ability" or a "unique characteristic". I don't think I've ever heard that before.