ARE PVC NESTBOXES SAFE?
Question: Are nestboxes made of PVC potentially harmful to birds because they might "off-gas" toxic substances during warm weather?
Short answer: I have not seen any evidence that a properly designed nestbox made of PVC is harmful to birds.
It is appropriate to be concerned about the environment eggs are laid in and that young birds will mature in. These are sensitive stages in development, and the nestbox environment is somewhat confined. When we invite birds to nest in our boxes, we want them to be as safe as possible.
A Gilbertson nestbox is made out of a PVC tube. The interior of standard Gilbertson boxes is coated with non-toxic paint. PVC is weather resistant, so the boxes will last a long time with minimal maintenance.
Certainly many thousands of birds have fledged successfully from Gilberston boxes. In my experience, chickadees prefer Gilbertson boxes.
A Gilbertson PVC box is one of the only boxes that is less inviting to House Sparrows (HOSP), a significant enemy of native cavity nesters. I find HOSP will usually pick a wooden nestbox over a PVC Gilbertson. It is also believed that they dislike the the small interior volume and short drop to the floor. Note that every nestbox style has pros and cons. Some bluebird landlords are concerned about the interior dimensions of this style box are cramped for growing bluebirds.
With regard to nestboxes made of plastic: as I understand it, the vinyl chloride component of polyvinyl chloride (PVC) is bound up in a polymer. While studies do show that toxic gases can be released when PVC is BURNED (e.g., incinerated as waste, or cut with lasers, torches, etc.), that is quite a different scenario from use as a nestbox.
I have not seen any studies that explored or determined that PVC nestboxes will offgas toxic gases under normal outdoor temperatures. Note: Keep in mind that the interior of a nestbox can get considerably warmer than outdoor temperatures, especially if it is not well ventilated or is placed in full sun in a hot climate. (See more on the topic of heat.) This might be a good research topic.
New PVC does have a bit of an odor. I expect it would dissipate when outdoors. GIlbertson boxes also have ventilation through the entrance hole and sides, and more small holes up top could be added if there is a concern.
In the past, plastics were considered pretty inert. We now know more about potential endocrine disrupters like BPA leaching out of plastic used to store food/water, etc. If someone wanted to be super duper safe and “all natural,” they could use nestboxes made of untreated wood.
Personally, I think bluebird landlords should focus their worries more on nestbox location, predator protection (including dealing with HOSP), and a nestbox that protects the contents from the elements (e.g., not soaking wet, freezing cold, or boiling hot inside.) (See more about nestbox safety, and pros and cons of various styles.)
But again, as far as I know, there are no studies indicating that a PVC nestbox releases toxic gases that would harm nesting birds. That’s not to say it’s not possible – just that I am not aware of any evidence supporting this particular concern.