The predator of my predator is my friend
There aren’t too many things that try to eat hummingbirds. They do face dangerous encounters with house cats, preying mantises or even spiders, but for the most part an adult hummingbird is too small and too maneuverable to be worth the effort to catch for a larger predator. Their eggs of course lack aeronautic defenses, like flying backwards, which makes them an attractive snack for neighbors like the Mexican jay. While hummingbirds are known to occasionally stab each other with their beaks, they don’t pose as much of a threat to a larger bird like the jay. They need help.
Bigger friends in high places
In the case of black-chinned hummingbirds (Archilochus alexandri) in Arizona, help comes from a hawk, at least indirectly. The Northern goshawks (Accipiter gentilis) and Cooper’s hawks (Accipiter cooperii) aren’t really interested in hummingbirds or their eggs. The Mexican jays, however, are large enough to make a meal, which has trained the jays to avoid hunting near hawk nests.
This all comes together where the hummingbirds build their nests within visual range of hawk nests, keeping the jays away. The 65 by 328-foot cone of visibility, and thus protection, makes a huge difference to the hummingbirds, with their chicks’ odds of survival increasing by 62%. The hummingbirds seem to appreciate the benefits of a guardian hawk in the area, as out of 342 nests observed over three years, 80% were built near hawk nests.
Source: Why a hawk is a hummingbird’s best friend by Elizabeth Pennisi, Science Magazine