Buffleheads have an extensive breeding range, with particularly high densities across the boreal regions of British Columbia, Alberta and Saskatchewan, and the sub-arctic deltas including the Athabasca and Slave River parklands. Buffleheads reach sexual maturity when they are about 2 years old. Pair bonds form during the first half of April (during spring migration) and they usually keep the same mate for years. During courtship, the male often puts on an extensive display. There are various displays he will initiate, but a common "dance" is the drake swimming with the bill up, neck stretched out, and head puffed to twice its normal size to show off its white head patch. He then might stand almost erect with his bill against his swelled breast, followed by a quick dive under the female. Throughout the display, there is much head bobbing and body movement from this energetic little duck.Buffleheads nest almost exclusively in tree cavities, and can squeeze through holes as small as 2.24 inches in diameter. The most common source of these cavities is old Northern Flicker holes that are often located 2-10 feet above the ground in poplar trees up to 200 hundred yards away from water. This eliminates most competition with other cavity nesters such as the Common Goldeneye; however, European Starlings and Northern Flickers still compete with Buffleheads for these nesting sites. Once females have successfully nested, many females will return to the same tree annually to nest.Nest initiation takes place between early May and mid May. Commonly, 10-14 eggs are laid and incubated for 28 – 33 days. Partway through incubation, the male will leave and gather with other post-breeding males for the wing molt. Buffleheads generally have high nest success, and the newly hatched young will spend 24 – 36 hours in the nest before jumping to the ground, where the hen will then lead the brood to nearby water. When ducklings are 5 – 6 weeks old, the female will leave, often before their first flight, which occurs at 50 – 55 days.