From the author:
"Video is often much more interesting when you speed it up or slow it
down, and the same is sometimes true with sound as well. In this case,
both the vocal sound and motion of hummingbirds are reduced in speed to
about 10x slower than real-life, causing the vocalizations they make to
become much more detailed than you normally get to hear. A few clips at
the beginning let us hear "normal" vocalizations of hummingbirds as
they squabble at the feeder for last-minute feeding rights at dusk.
The video was recorded in 848x480 resolution at 240fps using a GoPro Hero3+ Black edition, then slowed down to about 30 FPS for playback using GoPro's Studio software. The audio was slowed down roughly the same amount, and since no audio "stretch" effect was used, the pitch and
playback are simply lower and slower. The reverb effect is naturally
produced by the acoustically reflective hard surfaces around the feeder,
and are much longer and more more noticeable than in real time."