This is a completely new set of stats for an animal that really isn't any kind of a threat at all. The reason it needs stats at all though, is because it is conceivable that one might want to polymorph or wildshape into one... since they are quite hard to hit (high touch AC) and are extraordinarily fast. I tried my best to keep this as accurate to the real hummingbird as possible, and referenced hummingbirds.net  extensively. Also handy was the Immortal's Handbook, which told me exactly how much faster a hummingbird is compared to how the system expects how fast they should be.
Hummingbirds might also make exceptionally good familiars (with the Improved Familiar feat), as while they do no damage, a +16 to touch a target combined with the "Deliver touch spell" ability familiars have could be quite effective.
Hummingbird CR 1/2
, Senses ;
AC 26, touch 26, flat-footed 18 (+8 size, +8 Dex)
hp 1 (HD)
Spd 5 ft., fly 120 ft. (perfect)
Melee Touch +16 (no damage)
Space 0.29 ft.; Reach 0 ft.
Abilities, , , , ,
SQ Exceptional flight, metabolism, sustenance
Feats Weapon FinesseB
Skills Hide +24
Environment Temperate forests
Organization Solitary or pair
Level Adjustment +5
Exceptional Flight (Ex): A humming bird flies as fast as a creature 7 size catagories larger than it, except perfectly, and can use the Run action while doing so. While diving, the hummingbird gains the use of the Run feat as well.
Metabolism (Ex): A hummingbird's metabolism is so high it must consume more than its weight in food a day, in both insects and sugar water (mostly found in flowers). At any given moment, except when sleeping, a well-fed hummingbird is 1d4 hours away from starving to death. If administered poison, the secondary effect takes place immediately instead of a minute later. Ability damage is quadrupled, but also wears off in one fourth the time.
Sustenance (Sp): Twice a year, when migrating, the hummingbird acts as if wearing a Ring of Sustenance. This effect lasts for two weeks.