Oystercatchers (Haematopus ostralegus) are common shore birds across Africa, Eurasia and the Middle East. They often live in flocks and although most oystercatchers form monogamous pair bonds for breeding (you know, that story…), others have a very fun sex life.
Occasionally they get into a bisexual ménage à trois – two males with a female, or two females with a male – in which they all have an intimate relationship with each other. Females affectionately preen each other, males give each other courtship displays and all three have sex. These trios can last up to 12 years, aren’t always exclusive and members engage in hetero promiscuity outside the trio.
About 30% of oystercatcher populations are nonbreeding, but just the same, they engage in sexual behaviour within and without their bonded pairs and trios. Females sometimes top males and it has been estimated that a straight pair will have sex 700 times during the breeding season. 700 times for one single clutch of eggs. For oystercatchers at least, sex is about much more than just breeding.