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. HOWEVER, plastic CAN off gas, and eggs and nestlings will be exposed, although the implications are unknown. If you’re worried, stick to wooden nestboxes.
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. On my trail, when given a choice, bluebirds will choose a wooden nestbox over a plastic box.
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 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 off-gas toxic gases under normal outdoor temperatures. I also don’t know whether off-gassing is more likely in new versus aged plastic.
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 should use nestboxes made of untreated wood.
Plastic does last pretty much forever (which is not a good thing from an environmental standpoint.) Since roofs are usually the first to go on a wooden nestbox, a plastic roof on TOP of a wooden roof would help with durability. If spacers were placed inbetween the plastic and wooden roof, this would also help prevent overheating.
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.
MORE INFORMATION
- Nestbox Specifications – the proper size box for different bird species
- Nestbox styles, pros and cons
- Nestbox plans
- Heat and cold and nestboxes
- FAQs about bluebirding
- Bottom Line Advice for New Bluebirders
- Research topics
- House Sparrow Management and House Sparrow Identification
- Nest and Egg Identification
- Top Tips and Tricks to Attract Bluebirds to your yard
- How to Monitor Nestboxes
- Why Monitor?
- How to Start Your Own Bluebird Trail
Only we humans make waste that nature can’t digest.
– Captain Charles J Moore, oceanographer, who first brought the world’s attention to the Great Garbage Patch
