Anna's hummingbirds are a local hummingbird species in coastal central California living in the region year round. A few migratory species such as the Allen's hummingbird migrate through the region spending winter in Central America and summer further north. The birds are very territorial and will fight for the best food sources. A hummingbird feeder in the backyard is an unlimited source of easy food that is worth fighting for (so long as the human residents keep filling it).
Fights can get aggressive between rival hummingbirds, but typically a sequence of chirps and sometimes a game of chase is all that is needed for one bird to flee and another to gain dominance over a territory. The PowerPoint link below with embedded videos shows the chirps in the frequency range of 6-10kHz that can often be heard while a bird approaches the food source. The Acoustic Camera provided by Polytec and GFAI is used to capture these chirps as the hummingbirds fly through the air and to the feeder.
The Acoustic Camera was the first commercially viable system using beamforming to visually localize acoustic emissions. Brought to the market in 2001 as a pioneer technique, the Acoustic Camera has become a metaphor over the years for beamforming systems in general. The tool is now used in a variety of industries and has a growing customer base worldwide.
Link to the Power Point presentation here