Changes in precipitation patterns and fire ecology in some parts of the range could be impacting food sources and thus hummingbird populations.  Even hummingbird feeders could be an issue, by harboring disease, or altering natural behavior patterns. We lack the information to know what is limiting populations, or even if the decline is being adequately measured by broadscale bird counting efforts. Hopefully more study will fill in those essential knowledge gaps.  
In the north, few hummingbird-focused studies have taken place. To learn more about the Rufous Hummingbird in the temperate rain forest of Southeast Alaska, I began the Tongass Hummingbird Project began in 2013 near Juneau, Alaska,  with the goal to band hummingbirds at regular intervals with similar effort  each summer, using protocols adapted for Alaska from those used by the  Hummingbird Monitoring Network and Rocky Point Bird Observatory.
Some interesting patterns are emerging form the banding results.  Many adults are returning to the same spot each summer.  The recapture rates should over time yield an index of survivorship.  Several hummingbirds banded as juveniles have also returned.  Each bird is photographed, and we are observing  that while the red throat patches on females may become slightly larger and the back color of males may become slightly more red over time, the basic individual color pattern does not change. For example, if a female has just a few iridescent throat feathers the first year she was captured, she will still sport a small patch several years later. 
The Juneau station has not had the luck of catching birds banded on winter grounds, but part of an adult female’s migration was charted. After being banded in Alaska in July, she was encountered in a passerine migration station’s mist net near Lesser Slave Lake, Alberta Canada, over 700 straight-line miles away to the Southeast, just one week later. She had been logging over 100 miles a day and was safely released to continue her journey.
In addition to banding, supplemental information about hummingbirds is sought from local birders, such as reporting the first arrivals in the spring, the date young birds appear, and forage plants used. Now, in partnership with Juneau Audubon Society, the THP is creating educational materials to inform homeowners to make their yards more friendly for hummingbirds, and how to properly maintain feeders if they choose to put them up.
It is my hope that banders, researchers, and citizen scientists will find more ways to team up, gather meaningful and comparative data, and better understand what actions we can take to help protect these amazing little birds.
This project is possible thanks to support from the US Forest Service, countless local volunteers, and the advice and materials from the hummingbird banding community.