Buddha's birthday is a holiday observed by Mahayana Buddhists. It celebrates the birthday of Prince Siddhārtha Gautama, the founder of Buddhism. In many east Asian countries (except Japan) it is celebrated on the 8th day of the 4th month in the Chinese calendar.
World Fair Trade Day is an annual observance held on the second Saturday in May. It is held by the World Fair Trade Organization (WFTO), a global association of more than 300 hundred organizations that promote fair trade.
Astronomy Day is a bi-annual event, that is observed by astronomy enthusiasts, groups and professionals. The event originally started in the USA, but it spread to the other countries.
World Migratory Bird Day (WMBD) is an annual awareness campaign held on the second weekend in May. It is supported by the United Nations Environment Program as well as a number of international organizations.
Many countries around the world celebrate only one Arbor Day during the year. Mongolia is one of the few countries, that celebrates National Tree Planting Day twice a year. The tree planting events are organized on the second Saturday in May and October respectively.