Ruby-throated Hummngbird (Archilochus colubris)

Ruby-throated Hummingbird

In ‘Last of the Curlews’, by Fred Bosworth, a book reviewed by Stu Hills last month, I came across the intriguing statement that when migrating from Yucatan, hummingbirds start out at around the same time as other birds but outdistance all of them in crossing the Gulf of Mexico. It would take most birds around 20 hours to make the crossing, he said, the Eskimo Curlews could do it in ten hours, the hummingbirds would do it in eight.  I have long been amazed at how these tiny birds manage to cross the Gulf at all, but to do it in the shortest time of all other birds amazed me. So I started checking out a few hummingbird facts.

These are some of the cool things I found out.
In the days before beginning a migration, ruby-throats go into ‘hyperphagia’, a sort of feeding frenzy in which they spend more time than usual feeding on small insects (yes, insects) and nectar, and almost double their body mass, thus accumulating enough fat reserves to sustain them for their long, nonstop flight. When finally they reach landfall they will be in an emaciated condition and need to eat immediately or perish. Once on land their migration proceeds at an average rate of about 20 miles per day following the blooming of the flowers that hummingbirds prefer.
Hummingbirds on migration fly alone, even though they will use the same ‘highways’ as other hummingbirds. They may do this because flying individually they are too small to be seen by most predators, particularly as they skim over the water rather than fly high. Another reason may be that during hummingbird flight, there isn’t enough body mass to make a wake of air currents for others to follow, so flying in a flock provides no energy-saving advantage.
However interesting these facts may be, it is the anatomy of the hummingbird, enabling it to carry out these migration feats, which is truly mind-boggling.
Firstly, a hummingbird is incredibly light, weighing in at around 1/10th of an ounce. This makes the male, being slightly smaller than the female, no heavier than 2 and a half paper clips, or two males as heavy as a 5 cent coin. This extreme lightness in weight is achieved not only by its diminutive size, but also by its porous, and in some cases, hollow bones.
Secondly it has the greatest concentration of erythrocytes (red blood cells) than any other animal, and as we all remember from school biology days, the red blood cells are a principle means of delivering oxygen to the tissues. Combine this with a set of lungs that enable the hummingbird to breathe on average 250 times per minute and it is taking in loads of oxygen all the time. And to help even further, the hummingbird’s heart is a relatively large organ in comparison to its body weight making up between 1.75% and 2.5% of the bird’s total weight. This makes the hummingbird’s heart relatively speaking the largest heart in the animal kingdom. This mighty little heart beats 250 times per minute at rest and about 1,260 times per minute when flying.
All this oxygen powers that incredible engine, the hummingbird’s wings, which are unlike the wings of any other bird. They allow the bird to fly forward, backward, hover, and even fly upside down for a short period of time. A hummingbird can perform these amazing acrobatic feats for a number of reasons. First of all its shoulder joint is a ball and socket that allows the bird to rotate its wings 180 degrees in all directions. Hummingbird wings beat around 70 times per second in regular flight and up to 200 times per second when diving.  They don’t flap their wings, they rotate them in an oval pattern, except when they are hovering when they will move their wings in a figure-of-eight motion. In addition to this, the hummingbird, along with those fast flying swifts and swallows, have extremely long primary feathers and reduced secondaries. Primary feathers provide thrust, while secondary feathers provide lift. No surprise then that a hummingbird can fly at an average speed of 25-30 mph, and dive at a speed of up to 60 mph.
In crossing the Gulf of Mexico, a distance of around 500 miles, the hummingbird will wait for a tail wind of up to  20- 25 mph. This combined with its flight speed of around 25 mph, will bring it across to the US mainland in around 10-12 hours. This is slightly at odds with Fred Bosworth’s claim in ‘Last of the Curlews’ but latest research would indicate that this is closer to the current known facts.
Of all hummingbirds, the Ruby-throated is the best researched and there are some really good websites that document this bird.  World of Hummingbirds.comhummingbirds.net and hiltonpond.org  to name but a few. From this research we now know that while some hummingbirds take the land route through Central America others will for cross the Gulf of Mexico from the tip of the Yucatan Peninsula to mainland America and make the return journey to South America in the fall, thus making them the smallest of all migratory birds. And don’t forget that once in the United States these birds go on travelling as far north as southern Canada. And of course the Ruby-throated is the only hummingbird that breeds in the eastern United States.
There’s loads more I could say, but I’ll finish with a quote from Bill Hilton Jr who has conducted field research on the Ruby-throated Hummingbird for over ten years. He says, and who wouldn’t agree with him:
 “That any organism so small can carry out all its necessary life functions, including migrating a few thousand miles each spring and fall, never ceases to amaze me with awe and near disbelief”.
Glynnis Thomas