Coyotes are opportunistic, meaning they will grab a chicken (cat, small dog, etc...) if it is out in the open and easily gotten to. Where I live in the desert SW we have coyotes that will come and sit outside of our fence and howl (in frustration, I imagine) but won't jump the fence to get at the coop. Now, it is a perimeter fence with a coop fence they would also have to get through as well, so they don't even try. They either too lazy or too fearful or the rabbits are too abundant to make it worth their while to be proactive at getting to our birds. So, they wait for an opportune moment.
Before we had both fences they were taking birds almost every night, especially in the Spring and Fall. I think you may find it was a dog or even a pack of them that got your birds. Post if you do discover who did it.