我課本有個句子: One of the birds in the tree is white，the others are yellow. 想問一下為什麼兩個句子之間不用加and?

A semi-colon is the mark(;) used to separate the parts of a complicated sentence or items (white/yellow) in a detailed list, showing a pause that is longer than a comma but shorter tha a full stop/period,Not a colon.Since there is a semi-colon in between the clauses in the sentence, the word"and" can be omitted.
eg:-
One of the birds in the treeis white
(;)
the others are yellow.
no "and"

“One of the birds in the tree is white，the others are yellow.“

因為2⃣️句句子之間, 🈶️個「逗號」, 故 and 可以省略.

其他例子：
One of the birds in the tree is white, while the others are yellow.
樹上的其中一隻鳥是白色的，至於 其他的是黃色的。