I will bet you a dime to a doughnut, it is a cross between a pumpkin and a zucchini.
They are both from the same family. They are both
Cucurbita pepo (click). Wikipedia shouldn't say "Some Pumpkins." Really, all Jack o' Lantern pumpkins are Cucurbita pepo. Zucchini and pumpkins are frequently grown in American gardens and they
readily cross.
It is risky business to save a squash volunteer. My neighbor and I shared the same Tractor Guy who tilled the gardens for years. The neighbor allowed volunteer squash to grow one year - then left them in the garden.
I had his volunteers all over my garden! Unfortunately, they were in my own squash and pumpkin patches and it took me awhile to ID a few of the plants.
Just be happy that the chickens like them, Featherbaby. Chickens really do like the Cucurbita family a good deal. As far as how you might cook them - I haven't an idea for you there.
Steve