(Not really a cooking question, so GQ instead of CS)
There seems to be a connection between the internal temperature a plant or animal typically experiences and the melting point of it’s lipids; generally, they will have a solidification point slightly below that temperature. For plants, which are completely environment dependent, you have volatile oils like peppermint and spearmint for plants that grow in cold northern climates and waxy fats in tropical plants like coconut and palm oil. For animals, you have ectotherms like fish or reptiles that have oily body fats vs. mammals that have more solid fats like lard and tallow. Camels, which have among the highest body temperature of any mammal, have especially high melting point fats.
But this seemingly reliable correlation gets tossed out when you consider birds. They have high body temperatures, indeed higher than most mammals; yet at least for chicken, turkey and duck their rendered fat is essentially liquid at room temperature. So is the body temperature/ lipid melting point hypothesis false then, or is some other factor at work?
Lots of birds and other small critters go into topor on a regular (if not daily) basis to conserve … fat. Which in turn drops their temperature. If their fat congealed at that temperature … look out.
Body mass is sort of inversely related to the drop in temp during topor. And birds are fairly lightweight in general.
(The fact that we’ve bred chickens to be big doesn’t alter their basic biology. Their fat’s melting point is the same as their scrawnier wild ancestors.)
Here’s a paper with more data than you could hope for regarding topor. And not just an abstract!
CAUTION: WAGing during insufficient caffeination ahead.
Higher energy-to-mass ratio, mebbe? (That is, a more “energy-dense” form of fat.) ISTM that that woud be a pretty major evolutionary driver for birds.
If this coffee grants me the Miracle of Motivation in sufficient degree, maybe I’ll refresh myself on lipids … but for now, that’s my WAG, and mebbe if I wait long enough someone who knows what they’re talking about will come along and straighten us out.
Perhaps birds had no pressure to modify the more oily fats they inherited from their reptile ancestors. If retaining oily fats was not a detriment there may have been no selective pressure to modify it.
Waterfowl (such as ducks and geese) do tend to be more oily/greasy than land birds - that may or may not be related to the production of oils used to waterproof their feathers.