Field of Science

Global warming and hummingbird migrational timing

Our botanical geek tour scheduled earlier this year, but planned way back in February, almost came too late to see flowering displays of azaleas and rhododendrons.  This was no surprise by the time of the trip, but what are you going to do what with the airlines being so helpful about changing reservations.  Of course an earlier trip was out of the question because of semester demands, so little did it matter, and while annoying, it wasn't a tragedy and we got to see some magnificent yellow wood trees in full bloom.  However earlier flowering times as a result of global warming are a serious matter for some organisms.  Hummingbirds winter in the tropics and then fly north to breed in our temperate zone summers.  The advance on flowering dates is more pronounced at higher altitudes, and in places like the Rocky Mountains high meadows flowering begins on average 17 days earlier than 40 years ago.  This means that when hummingbirds show up more or less on schedule, some of the hummingbird's flowers have already come and gone.  And remember, this nectar is the food, the sustenance, for hummingbirds. How this will impact hummingbird breeding and migration is still not certain, but generally less food during your breeding season produces fewer offspring.  Although the study was about the birds, without their hummingbird pollinators, the plant reproduction was probably negatively affected too.  17 days is a long time at higher altitudes.  Could hummingbirds adjust?  Yes, for example, if those birds who migrate earliest have the most offspring, then natural selection could shift the instinctual behavior of when to migrate to an earlier time.  Other complications may exist like what is in flower and when along the migration route.  For example, this year our columbines were done before any hummingbirds showed up, so if this flower were a "filling station" to gas up their tanks, they would have been SOL.  Expect biologists to find many more examples as such trends continue.  

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