I've occasionally seen mention of half-gallon milk cartons being used for nesting boxes in field experiments. Not being a bird guy myself, I don't have any sense of whether or not this is widespread, either for research or for general efforts towards improving nest success in threatened species.
It would be great if it were, since I can't recycle milk cartons in my area (&#%$@!! red state) and would like them to have a new life as nesting cavities. If anyone uses milk cartons for their research, or knows of someone who does, please contact me off-list, I'd appreciate it very much. - J.
