"The four diseases that most frequently affect birds that use feeders are: salmonella, trichomoniasis, aspergillosis, and avian pox. All of these diseases are transmitted from one bird to another at feeding stations, especially when overcrowding occurs. Birds are also susceptible to mites and lice." (From: www.massaudubon.org)
Yet, it is remarkable, "With the exception of insects, hummingbirds while in flight have the highest metabolism of all animals – a necessity to support the rapid beating of their wings during hovering and fast forward flight. Their heart rate can reach as high as 1,260 beats per minute, a rate once measured in a blue-throated hummingbird, with a breathing rate of 250 breaths per minute,..With the exception of insects, hummingbirds while in flight have the highest metabolism of all animals – a necessity to support the rapid beating of their wings during hovering and fast forward flight...Their heart rate can reach as high as 1,260 beats per minute, a rate once measured in a blue-throated hummingbird, with a breathing rate of 250 breaths per minute..." From Wikipedia "Hummingbirds" Both articles online 8-25-17