Many people will use galvanized steel to build cages or large enclosures because it's an inexpensive way to enclose a large area. Most believe it's perfectly safe for a parrot but the truth is, it depends on how the surface is treated because 'galvanizing' includes the application of zinc.
Zinc is one of the many "heavy metals" that can become deadly if ingested in toxic levels. Zinc is one of the leading causes of heavy metal poisoning in birds because it's everywhere in your birds environment ... from the clasps to chains to the bells on their toys. Why? Because it's cheaper than stainless steel.
Now Zinc, in very small amounts, is an essential element found in the body. It's a trace element needed for the body's immune system to work properly, and it plays a role in cell division and growth, wound healing, and breaking down carbohydrates. What we are talking about here are high levels of zinc that will result in zinc poisoning. There are a number of heavy metals that will result in heavy metal poisoning which is discussed in the "Test Your Metal" blog, but let's talk about the process of galvanization because this is what's often used for large enclosures.
Hot Dipped Galvanized (HDG) steel goes through many stages, which are listed below so you can make your own decision on whether you want to make an enclosure from this material (information was obtained from a website explaining how to paint or coat galvanized steel).
Stages of Galvanized Steel
Brand New Hot-Dipped Galvanized (HDG) steel contains five layers with a surface layer of 100% zinc (shiny). Putting a bird in a brand new enclosure would expose it to high levels of zinc that is would ingest as it climbs around on the enclosure.
The pure zinc layer reacts with atmospheric oxygen (O2) and forms a zinc oxide (OH2) layer. This second stage is as unstable for coating, as is the first stage, and normally occurs in the first 48 hours.
The zinc oxide layer reacts with moisture in the atmosphere to form zinc hydroxide. This is also an unstable form of HDG requiring special procedures to properly coat, if you were going to paint or powder coat the enclosure. This third stage can take from 48 hours to six months to occur.
Zinc hydroxide reacts with carbon dioxide in the atmosphere to form zinc carbamate. This is considered first stage of weathered (aged) galvanized steel in that it is now a stable form of zinc for coatings purposes. This stage can take from six months to two years to achieve. This can be accelerated by the application of a diluted vinegar solution. [more information on oxidizing]
The second stage of aged galvanized steel can take a short time to many decades to occur. It can be described as fully weathered galvanized HDG steel that has not yet begun to corrode or has very little of the zinc/iron alloy layer showing with little to no staining from exposed layers of zinc or iron.
The third stage of weathering is where less than 10% of the surface area is showing signs of corrosion and/or zinc/iron alloy staining.
The fourth stage of weathering is where 10-50% of the surface area is showing signs of corrosion and/or zinc/iron alloy staining.
In the fifth 5th stage of weathering, 50-90% of the surface area showing signs of corrosion and/or zinc/iron alloy staining, and some pitting corrosion as well.
And by the last stage of weathering, 100% of the surface area is corroded and little to zero galvanized remaining; the condition of the material is closer to pitted corroded carbon steel as no galvanized remains.
The symptoms of zinc toxicity are depression, vomiting, ataxia, and death. Zinc toxicity can be determined through blood screening or X-ray, but sometimes particles will not show. Treatment for zinc poisoning is chelation therapy.
Many outdoor cages and aviaries are made with galvanized steel and there is a chance that your bird can be exposed to zinc as it uses its beak to climb around the enclosure, so it's up to you to decide. I would much rather see birds outside in the fresh air and sunshine so I would use galvanized panels for an aviary. You can also but items like nets and large branches so your bird will be less likely to climb around the metal panels. Still it is always an individual choice.
As far as toys and hardware used in the cage, I only use stainless steel mounting brackets, clips, chains, and bells because these items are shiny and likely an alloy mixed with other metals such as nickel and silver, which are also heavy metals. I try to buy from toy manufacturers who use stainless steel, but for those that don't I remove the original hardware and replace it with stainless steel clips and chains, and I always remove the bells. Before discarding those toys, I remove your stainless steel items and save for the next time. Yes this costs more and a little more effort but it's worth it to me.
Here are a couple more resources on the subject.
From Avian Medicine Principles and Applications
Chapter 37, Toxins by Genevieve Dumonceaux and Greg J. Harrison.
"Zinc is another frequently encountered heavy metal that causes toxicity when ingested by birds. Zinc toxicosis should be included in the differential list when heavy metal intoxication is suspected. Galvanized wire and the clips used to construct enclosures are common sources of zinc. The clinical syndromeescribed in birds that ingest zinc from a wire enclo- sure is frequently referred to as “new wire disease.”40 The brighter and shinier the wire, the higher the zinc level.21 The occurrence of “new wire disease” can be reduced (but not eliminated) by scrubbing the wire with a brush and mild acidic solution (vinegar).50 Galvanized wire may also contain lead.40 Some gal- vanized coatings contain 99.9% zinc while others are 98% zinc and 1% lead. The white rust associated with the galvanized coating is also toxic.21 Galvanized containers and dishes are other sources of zinc con- tamination.27 Pennies minted in the USA since 1982 contain from 96% to 98% zinc that is coated with copper.1,29,30,40 Monopoly game pieces are made of 98% zinc."
The National Institute of Health (NIH) posted an article on housing psittacines in galvanized enclosures and here is the abstract of that article [https://www.ncbi.nlm.nih.gov/pubmed/1624342].
Each week over a 6-week period, 80 adult cockatiels (Nymphicus hollandicus) of either gender were dosed orally with fine particles of pure zinc or galvanized coating removed from welded wire mesh. At dosage of 32 mg/wk, all birds became severely ill and either died or were euthanatized within 2 weeks. Dosage of 2 mg/wk induced chronic illness marked by dullness, weight loss, and intermittent excretion of greenish droppings. Necropsy findings were unremarkable, except for signs suggestive of impaired gastrointestinal tract motility and histologic degenerative changes associated with focal mononuclear infiltration in the liver, kidneys, and pancreas. Tissue, especially pancreatic, contents of zinc were markedly high. Pure zinc was as toxic as galvanizing zinc. White rust, an oxidation product, also was toxic. The galvanized coating on cages and flights must be carefully wire brushed and examined before housing psittacine bird.
Original post revised March 14, 2020