You can try add some flour on every floor edges and watch the every morning. Maybe you will distinguish the marks of chickens and snake and see where did it passed by.
Or maybe you can try provide a good warm shelter to the snake and watch it every day.
This are the methods that we use when the snakes are missing...
(Sorry for the english.

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I gotta say, flour is a brilliant idea and I'm a bit ashamed as a theoretically cunning human that I didn't think of doing something like that.
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OP you said there was a rainforest and foxtail palms everywhere, any chance you are in Cairns, Port Douglas, Mossman area?
West Brisbane by the river. The rainforest is only in a small patch in our backyard, and also has pecans and a large macadamia (thus the bush rats). It was planted by a garden enthusiast about 25 years ago and well before we moved in and has many north qld plants and the bunches of foxtails are giant and fruiting. We have MANY brown snakes here from the river, I have also seen a Coastal Taipan and of course carpets. No black snakes.
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How big is the mesh?? If it is a snake and it is large enough to take "teenage chickens" its going to be a fair size snake and reasonably easy to spot i would imagine. The snake might have been able to get through the mesh, but if it is eating chickens then i doubt it would get back through the mesh. If the mesh is big enough for the snake to get back through then there is a fair chance that the chooks would be able to get through it as well.
This is really something I need info on - I couldn't find the snake in a quick search this afternoon but I must admit I was scared too dig around in the hay. The pen has normal chicken wire, double layer around the bottom, and now also has aviary mesh we have dug in but only along one side so far (will get to the rest next week). I do not know how well snakes can squish through things but it has had trouble getting two out, I found them stuffed against a stretched out hole in one corner not a scratch on them but throttled and beat up. The others just gone. I was thinking perhaps they "crushed" the teenage chickens inside them or something and could squish out but I'm also worried it could be in the pen. My husband says twaddle, carpet snakes like living up trees and won't be under the gravel but I am not sure, what do you guys know about carpet snakes would it really live under a nesting box? I have two nesting boxes on the ground both with broody hens in them at the moment that I have not looked under yet!
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Im not sure it is a snake
reason being 2 in 2 nights
unless of course you have a family moving in??
'snakes in the chookhouse??
possibly a monitor would clean up a couple in 2 days
but a decent sized chook is plenty for most pythons
with that in the gut they will just rest up for at least 3 or 4 days
so no reason for one python to return within 24hours
Kind of what I thought! I think I need to get a night vision camera *sigh*. Are carpets territorial or could there be more than one? It is not a monitor, I am certain one could not get in and I would surely see a goanna at some point rustling up a tree if one were around. We have plenty of water dragons however they can't get in as I keep having to rescue the idiots who get stuck in the door running past when I leave it open.
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Fairly certain it's impregnable to cats, dogs, and hawks. I had trouble with crows getting in to start with so it's fairly secure, I think... definitely need to go check ebay for night cameras...
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Oh and our browns grow to very large size around here, most I see are around 2 metre mark... have seen them in the pen before but hoped they were just rat snakes and not chicken snakes... oh and my roo survived a tangle so thinking not poisonous because of that.... but would they be more likely to live IN a pen on the ground than a python?