Gold jewellery often contains an engraved marking such as a number, letter or combination. This is because many countries, including the United States and Canada, require that gold is authenticated by the manufacturer. The engraving in the gold usually indicates the amount of carats that it consists. However, many manufacturers use or used to use a hallmark, which is a symbol unique to the manufacturer. Animal hallmarks can also indicate the country where the gold jewellery was made.
Research the history of gold hallmarks for different countries to find out which ones commonly used birds and animals on their gold. For example, France rarely used numbers and commonly used animals and heads of animals, such as insects and birds, to indicate the fineness of the gold, the location of the manufacturer, and whether the gold was an import or export.
Consult a book such as Tardy's Hallmarks on Silver. Although the book focuses primarily on silver jewellery, it will give you some examples and understanding of the different hallmarks used in jewellery, both gold and silver.
Find a company that specialises in identifying gold hallmark birds, such as Gold Traders (see Resources). A quote can be obtained by measuring the gold jewellery in grams and the amount of carats. You can measure the gold jewellery by using a kitchen or postage scale. Click on the hallmark symbol that appears on your jewellery. It will tell you where your item was assayed.