Help! .......4 dead!

I have been raising these 8 for 4months now. They have been outside in there own pen for 2 months. Eating game raiser and assorted wheat, corn, and oats as I get them. I have been raising them with the intention of allowing them to free range and reduce my bug population without eating my garden like the chickens do when they free range. I just let them out over the weekend to go free range and they seem to be doing fine. Eating drinking and roosting on top of their cage instead of inside it now but other wise safe. I came home today and only found four together, they are usually all togethere. Well I walked around by the barn and found 3 bodies within about 20 feet of each other lying on the ground and one over by the roost. The bodies were not torn apart but seemed to have some ruffled breast feathers, otherwise they just looked like they laid over and died.
I need help to determine what happened so I can save the rest of them. I will catch them tonight on the roosts and put them back in the pen.

Any ideas what happened? We have horses and goats but everyone seemed to get along. We also have a lab that has committed chicken murder by suffocation in the past but I don't think thats what happened, possible but don't think so. Is there anything that is poisonous to them or possibly a problem with there crops?

Please, any advice?

I will process them and open them up to see if there is anything obvious. Any help here would be appreciated as in what to look for in the crop and internal organs. I am use to processing my own chickens and game so not squimish a bit, just tell me what to look for!

My guess would be a dog. Dogs kill multiple birds, do not eat them. They just kill for fun.

Very odd mystery deaths, and even more so odd that they were so close together... without any external injuries, no sign of struggle or any scattered feathers I'd have to guess that they must have eaten something toxic... but what? Do you have any snail/slug baits or even rodent bait that they would have had access to in the past few days? Any overheated vehicles leaking antifreeze into the ground that they might have gulped up or anything? What about over at your neighbors'?

Sorry for your loss... I have no idea what to look for inside the birds, it's hard to even guess what could have taken 4 out in such a short time period other than some sort of toxin.

Yea....I thought about the poisons and liquids but no other chickens or other animals have shown any signs or symptoms of sickness. I don't have any poisons on the property and no free standing liquids that could have held anything poison like antifreeze. I have two 5 gallon waters for all the animals to drink from.

Well I completed the butchering on the birds and was very careful in skinning and looking at the organs. The crops were full with about a 1.5 -2.0 round ball of grains, grasses and small pebbles. Also contained some fluid. The intestines showed no bulging and the gizzards were full of the same feed and grass a long with at least 8-12 round gravel pieces no larger than .20 of an inch. The livers had good red coloring along with the hearts. The vents were clear and did not seem to have any impacting.
The breasts showed no bruising and neither did the legs or backs. No bleeding was noted from the ears or mouths either.

This really has me stumped.
So when I went to grab the live ones tonight I was able to get only one. And for the first time ever the other 3 took off flying into the trees about 200-300 feet away landing high up in the trees. There was a lot of impact noises which scares me that they hurt themselves.

Anyway any help or guess are welcome.

This morning I went out to check on them and found the remaining 4 together. I was able catch one last night and put it into the pen. The other three came back and they are walking around the pen trying to spring their buddy!

I am adding some more info here on the deaths to help determine what caused these four to die off. The area where they died was at the back of the barn where the horse manure is piled up. We also place our food scraps back here for the chickens and goats to pick through as they wish. The contents from what i can remember is as listed: Cooked corn, raw corn, lettuce, potato's, carrot peels, hamburger buns, bread, avocado peels, orange rind, grapefruit rind, onions, hamburger meat, hot dogs, grapes, pickles, cottage cheese.

It makes sense to me that they died eating something from that pile but I have no idea what it could have been. Are we inadvertently poisoning the Guinea's with the food scraps. As I said before no other chickens or animals have had any ill effects just these four Guineas.

Did you ever figure out the mystery?