It seems fairly straightforward to me..when it is expensive to procreate due to restricted resources, procreation becomes picky. Birds are mostly monogamous because flying is very energy intensive and the male parent doesn’t want to waste resource on fledglings that isn’t his..obviously, exceptions exist. It is very costly to raise the young. Parental investment is high.

It is different for birds that don’t fly. Water fowl especially have a different reproductive system. Because they don’t fly. This is true for all flightless birds. Even for birds like geese that only fly for seasonal migration. They get their food from the water. Ground dwellers have plenty of food and don’t have spend as much energy foraging for food as a bird that flies. Very few of them mate for life.

Further: Galus Galus has different design than geese and ducks. Castrated roosters are called ‘capons’(French)…produces a nice soft fat capon for Sunday lunch. It’s genitalia is less developed than say..geese.

As a chef, I knew how to sex identify geese/duck. water fowl genitalia is different than fowl. Most farmers know this as sex determination is key to raising animals for profit. With the exception of Pilgrim/Emden/White Italian and some Chinese geese where the autosexing is straightforward with feather colouring and down colour, most have to be identified while they are still goslings.

Goslings can be gender identified as early as the first week and also when they are adults. Male adult penis is invaginated and like a corkscrew. Female organs has genital eminence. The breeding ratio is 1:3 or max 1:5. So it’s important to separate them as early as possible.

Mammals are different..example: feline penii is barbed and most copulation results in kittens. A female cat can have a single litter with multiple tomcats. Male cats will kill kittens ..probably those that aren’t their own..because a lactating mother cat won’t go into heat.

With insects like bees and mantii, the male often meets his end after sex. It comes down to energy needs and availability of resources.

P.S: [..] Birds, she thought at the time, didn’t have penises. In her two years studying them at Cornell University, a world leader in avian research, she’d never once heard her colleagues mention a bird penis.[..] Huh! Really? Cornell university scientists don’t know what a farm child picks up during one farming season? The article is full of red flags for clickbait lies.