Thursday, December 26, 2013

Banding Ruby-throats at the Finca

We have ten species of hummingbirds that regularly visit the feeders here at Finca Pura Vida, including one which we have the great pleasure of knowing on both ends of its range, the tiny Ruby-throated Hummingbird (pictured below).  Weighing in at just 3.5 grams (less than the weight of a nickel), they are the smallest hummingbird that visits the feeders at the Finca.  They are also distinguished by the fact that they are the only species found here that migrates to and from North America, often travelling 600+ miles nonstop across the Gulf of Mexico to reach Middle America sooner.

In the interest of providing data for studies involving demographics of bird populations, we must determine the age and sex of each Ruby-throated Hummingbird we capture and band.  Only adult male Ruby-throats have the ruby-throat, which makes identifying adult males a cinch.  Things get a little tougher, however, when faced with immature males, immature females, and adult females, all of which can look remarkably similar (an immature female is shown below).  

It is not impossible to determine the sex and age of most of these confusing Ruby-throats; in fact, with some practice, just about every bird we catch can be assigned to one age/sex class.  Many - but not all - immature males have some "stubble", some dark stippling on the throat where the ruby gorget feathers are soon to appear.  Some begin acquiring ruby throat feathers around this time of year, which facilitates their identification as males, as pictured in the photo below of a male with a partial ruby gorget.

Another way to check the bird's sex is to note the shape of the bird's sixth primary flight feather (the feather on the left in the photo below); the tip of the feather is rounded in females, and pointed in males.  The wing pictured below belongs to an adult male.

It is astounding that these tiny birds weighing less than a teaspoon of sugar can travel many hundreds of miles to spend the winter in tropical climates.  The fact that we have such a high concentration of these little creatures here at Finca Pura Vida means that we can contribute much-needed information about their poorly-understood winter biology.  What more could a group of bird-lovers ask for?

Placing a numbered metal band on the leg of a Ruby-throated Hummingbird

No comments:

Post a Comment