1. Hummingbirds: Hummingbirds are known for their tiny size and their ability to hover in mid-air. They typically lay one or two eggs at a time, which are incubated for about 12-14 days.
2. Pigeons and Doves: Most pigeon and dove species typically lay one or two eggs at a time, which are incubated by both parents. The eggs hatch after about 18-24 days.
3. Ostriches: Ostriches, which are the largest living birds, lay one egg at a time. These eggs are among the largest of all birds, weighing up to 1.4 kilograms (3.1 pounds). They are incubated for about 40-45 days.
4. Emus: Emus, which are native to Australia, also lay one egg at a time. These eggs are incubated by the male emu and hatch after about 56-60 days.
5. Kiwis: Kiwis, which are found in New Zealand, lay one or two eggs at a time. These eggs are incubated by the male kiwi and hatch after about 75-85 days.
These are some of the bird species that typically lay one egg at a time, although there may be variations among different species and individual birds.