Prunus padus, known as bird cherry, hackberry (unrelated to the genus Celtis), hagberry, or Mayday tree, is a flowering plant in the rose family.

In Asia it is found throughout the forests of Siberia, Mongolia, the Russian Far East, Korea, Hokkaido, and parts of China with pockets in the Himalayas It is an invasive species in Alaska, prompting efforts at eradication.

[citation needed] The glycosides prulaurasin and amygdalin, which can be poisonous to some mammals, are present in some parts of P. padus, including the leaves, stems and fruits.

This juice and the "cakes" produced in its manufacture were, according to Herodotus (who derived his account from the reports of Scythian traders), the main sustenance of the "bald people".

These are they who judge in the quarrels between their neighbours; moreover, whatever banished man has taken refuge with them is wronged by none.— Herodotus, Ἱστορίαι (The Histories) Book IV, Chapter 23In Finland and Sweden, the blooming of bird cherry (Finnish tuomi, Swedish hägg) signifies the start of the summer for many people.

[citation needed] A taboo on the use of the wood of the hackberry (or hagberry) was reported by natives of Advie, in northeast Scotland, who believed it to be a "witches' tree".

[clarification needed] The Mayday tree is abundant as an introduced species in Anchorage, Alaska, having been planted in great numbers by landscapers and homeowners.