I remember reading years ago in Consumer Reports about formaldehyde outgassing or offgassing from home products such as textiles, carpet, etc. Some people were highly sensitiive to it. Rather than doing too much typing, I have provided web-links below from Google result on "formaldehyde test".
If you cut down a tree (most types of trees) you will see it decay over a short period of time. Termites and other insects and mold don't readily attack finished wood and textile products in houses, furniture, carpet, wallpaper, plywood and the like because of chemicals used in the manufacturing process. As with any human endeavor ("The best-laid plans of mice and men" - Robert Burns) mistakes, mishaps, glitches occur, and a defective batch or production run makes it to the end user or consumer. Formaldehyde is a basic ingredient in many manufacturing processes. Manufacturing standards of permitted levels of outgassing may be tolerable for most humans and even for pregnant women, but not necessarily tolerable for birds. Coal miners used caged canaries to detect poisonous gases: if the bird fell over dead, get out!
If I had baby pigeons dying from unknown causes I would do as others here have done: get the opinions of others, try a few things out. If I tried several things out, got good results, still didn't feel certain of the cause, harbored some strong suspicions, I would pass on the basic facts of what I had done to those who could take it a step further. A former employer once insisted on legally-acceptable, undeniable, evidentiary ways of putting someone on notice, such as paper records in the form of teletypes, notarized forms, faxes. Establishing who you are, whom you are addressing, who will get copies now or who may get copies in the future, and letting them know you are keeping records, establishes your bona fides and intentions.
If I were the salesman, retailer, wholesaler, distributor or whatever, I would want to be informed by the end user or the one next in line between me and the end user, so that I could take direct action, pass it on, or do both, whichever was appropriate. I probably not want to wait to be informed until after the end user had confirmed or proved his suspicions or hypotheses. I might not like bad news, but if responsible I should welcome being informed. It would be to my benefit. Being put on notice by something provable and undeniable (such as something in writing) might help me to defer judgement if I were not competent and to pass it on to the appropriate party. (I think CYA "cover your ass" is acceptable when coupled with maximum responsibility).
Someone along the line would then be able to determine the correct cut-off point. A statistician or someone versed in these principles can determine what information is usable and valid. Possibly what manufacturing batches to sample, or what limitations to establish in product or process use, or what warnings, caveats to issue.
If the reader gets this far, I apologize if I have been pedantic or too wordy. It often helps me to clarify my thoughts by writing it out. Perhaps I am the main and solitary beneficiary, but I don't think I destroy too many trees in the process, and I don't force anyone to read it. Except the poor moderators.
Web-links below from Google result on "formaldehyde test":