I was thinking it might get a bit hot on a sunny day and that they may well peck away at the plastic, but I guess it can work after-all. Out of passing interest though, did they peck the plastic cover [member=4333]Fleecewife[/member]?
No, the hens never did, nor ducks. The geese dibble it if they get anywhere near the tunnel although I think the polythene is too tough for them to get through (the strongest you can get against the wind). The only creature which has damaged the cover was a 4 horned Jacob wether, who used his horns to cut out a neat triangle so he and his chums could climb through and demolish my winter brassicas. The repair tape is great and lasts for years!
Our tunnel is well ventilated with big louvres and double doors at each end, so the hens have never been too hot. They had a small house inside for nights and egg laying, and to provide shelter from direct sun. I have never had the hens in there during the summer though - the temp can get up to 100F in the tunnel if there's no wind.