Copper birdbaths and the possibility of copper toxicosis in wild birds
Please note: This document is a review of the academic literature relating to copper toxicosis in wild birds. The review was conducted out of frustration with uninformed opinions concerning the potential dangers of copper birdbaths to wild birds. It should be noted that I am not a scientist, and I would be happy to discuss this document or be presented with any further evidence.
There is no clear evidence, in the scientific literature, that water drunk from a copper vessel poses any kind of health threat to wild birds. Nor are there any credible reports of the same. That said, copper toxicosis is known to occur in wild birds. It is typically a result of birds frequenting sites that are contaminated by industrial activity and mining. The question of the toxicity of copper to wildlife is one that concerns the quantities that the animal is exposed to. In this document, research concerning heavy metal poisoning in birdlife is reviewed, and a projection of the likely hood of copper toxicosis in birds, resulting from drinking water in a copper vessel, is made. The general conclusion is that it seems incredibly unlikely that there might be enough copper leaching into the water contained in a copper birdbath to harm birds.
Copper is essential for the normal growth and metabolism of all living organisms including birds (Eisler, 1998). Different animals react differently to exposure to copper. Sheep and cattle are often affected by copper toxicosis. Birds (and mammals) are considered relatively resistant to copper (Eisler, 1998). There are quite a few reports of copper toxicosis in the commercial avian industry (poultry farming, etc.) and some in wild birds. These are all discussed below.
One source for the fear that copper might contaminate drinking water for birds comes from reports of heavy metal toxicosis resulting from putting USA copper pennies into pet birds' drinking water. This is usually done to reduce algae growth in the water. Copper pennies are a known source of zinc toxicosis in birds (Richardson, 2006; Droual, Meteyer, and Galey, 1991), not copper toxicosis. As reported by Richardson (2006): "Pennies minted since 1983 contain 99.2% zinc and 0.8% copper and one penny contains approximately 2440 mg of elemental zinc." Zinc and lead toxicosis are much reported in pet birds (Richardson, 2006; Lightfoot and Yeager, 2008; LaBonde, 1995). LaBonde (1995) says that heavy-metal toxicities other than lead and zinc rarely occur in pet birds. Copper toxicosis in pet birds is usually the result of the ingestion of copper pieces.
"Prior to treatment, blooms of Anabaena flos-aquae, Aphanizomenon flos-aquae, and Microcystis aeruginosa were associated with deaths of migratory waterfowl, game birds, songbirds, game, and domestic animals (Rose 1954). Most of these species of algae were controlled within 24 h by 1.0 mg Cu/L as copper sulfate. Copper treatment had no adverse effects on bottom fauna but populations of crustaceans (daphnids, copepods, entomostracans) were reduced. One year after treatment no deaths of birds or mammals were recorded (Rose 1954). "
This report highlights copper's known benefit to birds when added to water; it reduces algae, but does little to establish what might be considered a non-toxic dose of copper.
Eisler (1998) reports on the effects of controlled doses of copper fed to mallards, ducks and domestic chickens. Studies cited experimented with scales of dosage levels;
Day-old chicks only began to show signs of adverse affects when the copper component of their diet reached 350mg/kg. Other studies show high gizzard erosion with copper densities of 500 and 1,000 mg/kg (fed for 4 weeks). Young Turkeys only showed negative signs when fed 800mg/kg:
"Week-old poults fed corn-soybean meal supplemented with 100 to 800 mg/kg ration: No adverse effects on survival; growth reduced only at 800 mg/kg diet" Eisler (1998)
Mallards showed a preference for water with a certain amount of copper.
"Mallards seem to prefer drinking water containing 100 mg Cu/L over distilled water (Table 6); however, these birds were molting and this may have influenced their response because trace mineral requirements rise during molting (Rowe and Prince 1983)." Eisler (1998)
Comparatively, humans are far less tolerant to copper than birds. Copper toxicosis is observed in human infants after drinking water with a copper concentration of 3 mg/L for 9 months (Eisler 1998). In Australia the safe drinking water concentration of copper is 2mg/L. Eisler (1998) notes that the conduction of water in copper pipes can be responsible for introducing up to 1mg of copper per litre of water.
The above figures are sufficient to make a crude projection. If the water used to fill a copper birdbath came from copper pipes then its copper content may already be up to 1mg/L. Assuming that a copper birdbath will leach around as much copper into the water as water pipes do, then it will contribute another 1mg/L, for a total of 2mg/L. This concentration of copper is 50 times less than the safe levels consumed by mallards as mentioned above.
Lead toxicosis is much reported in wild birds ( Lucia, André, Gontier, Diot, Veiga, and Davail, 2010; Lewis, Poppenga, Davidson, Fischer, and Morgan, 2001).
There are few reports of copper toxicosis in wild birds. One study (Henderson, Winterfield, 1975) reports lesions in Canada geese after having ingested copper sulfate at about 600 mg/L of water from a small man-made pond. In acidic environments where, for example, acid rain is known to occur, copper birdbaths are likely to produce copper sulfates. However, given that the copper content of the water will be around 2mg/L, concentrations of copper sulphates will be one or two orders of magnitude lower than the reportedly toxic 600mg/L.
In a paper published in 2008, Thomas, and McGill make an analysis of the potential toxicology of birds ingesting sintered tungsten–bronze (containing 44.4% copper). Sintered tungsten–bronze is a suggested substitute for lead used in discharged lead shots and fishing weights, which are known to cause lead poisoning in wild birds. Thomas, and McGill simulated the ingestion of eight sintered tungsten–bronze spheres in ducks to observe the effective rate of release of copper into the ducks' digestive system. They conclude:
"The release of 43.17 mg copper/day from eight tungsten–bronze spheres, while exceeding the daily copper requirements of domesticated birds, is far below the levels of copper known to cause copper toxicosis in birds." (Thomas, and McGill 2008)
For a bird to ingest the equivalent of 43.17 mg of copper/day by drinking water from a copper vessel, it would have to drink in excess of 20L of water in a day. Lets assume that the above estimation that a copper birdbath will leach 1mg of copper for each litre of water is wrong by an order of magnitude: if a copper birdbath was to leach 10mg of copper for each litre of water, a wild bird would still need to consume 2L of water per day to approach the copper concentration that Thomas, and McGill say is still safe.
Notwithstanding the differences in bird species, in their specific diets, in the proportions of water ingested from a birdbath and ingested through vegetable matter or other water sources, in the different types of copper compounds that may be present in the water consumed; it still seems incredibly unlikely that water ingested from a copper vessel will pose a credible health risk to wild birds.
Eisler, R., 1998. Copper hazards to fish, wildlife, and invertebrates: A synoptic review(No. USGS/BRD/BSR--1997-0002). GEOLOGICAL SURVEY WASHINGTON DC. (http://www.pebblescience.org/OLD-SITE/pdfs/CHR_33_Copper.pdf)
Thomas, V.G. and McGill, I.R., 2008. Dissolution of copper, tin, and iron from sintered tungsten–bronze spheres in a simulated avian gizzard, and an assessment of their potential toxicity to birds. Science of the total environment, 394(2), pp.283-289.
Lightfoot, T.L. and Yeager, J.M., 2008. Pet bird toxicity and related environmental concerns. Veterinary Clinics of North America: Exotic Animal Practice, 11(2), pp.229-259.
Richardson, J.A., 2006. Implications of toxic substances in clinical disorders. Clinical avian medicine. Spix Publishing Inc., Florida, pp.711-719.
LaBonde, J., 1995, January. Toxicity in pet avian patients. In Seminars in Avian and Exotic Pet Medicine (Vol. 4, No. 1, pp. 23-31). WB Saunders.
Lucia, M., André, J.M., Gontier, K., Diot, N., Veiga, J. and Davail, S., 2010. Trace element concentrations (mercury, cadmium, copper, zinc, lead, aluminium, nickel, arsenic, and selenium) in some aquatic birds of the Southwest Atlantic Coast of France. Archives of environmental contamination and toxicology, 58(3), pp.844-853.
Lewis, L.A., Poppenga, R.J., Davidson, W.R., Fischer, J.R. and Morgan, K.A., 2001. Lead toxicosis and trace element levels in wild birds and mammals at a firearms training facility. Archives of Environmental Contamination and Toxicology, 41(2), pp.208-214.
Henderson, B.M. and Winterfield, R.W., 1975. Acute copper toxicosis in the Canada goose. Avian Diseases, pp.385-387.
Droual, R., Meteyer, C.U. and Galey, F.D., 1991. Zinc toxicosis due to ingestion of a penny in a gray-headed chachalaca (Ortalis cinereiceps). Avian Diseases, pp.1007-1011.