Flying Emeralds

Well, the fire flies are finished for the year.  But the June light show has been replaced by the ongoing antics of our single species of hummingbird, the Ruby-throated hummingbird.
As you all know, it’s his throat that glistens like a ruby, especially when he finds another hummer in his patch.

As far as I’m concerned, hummingbirds can’t be described adequately by human language. They are at once busy, irritable, glistening projectiles that dart around as it fired from a gun. But they are also capable of turning on a dime, making the air whistle as they do so. 

There might be a few more than 350 extant species, all of them living in the “new world.” There are hovering, nectar-feeding birds in Africa and Asia (sunbirds), but while they can be very colorful, they are inept in the air when compared to hummers. In the U.S., we can regularly find fifteen or so. Diversity peaks in southeast Arizona, where the western Sierra of Mexico pushes into the U.S. If you know where to go, five or six can be seen without much trouble.

Back here (east of the Mississippi), we’re relatively deprived, but our little gem has a lot to tell us.  At 3.5 grams, it weights just a third more than a penny. It’s tiny size puts demands on it that even a small rodent like a mouse couldn’t understand. Basically the bird has a white-hot metabolism that needs to be fed constantly. If you see one lounging about, it’s waiting for its crop’s contents to drain into the stomach. Then it’s on the go again. But what about food during the long night, what then? Basically, they “hibernate” each night. It’s called torpor.  The body temperature is dropped, therefore the driving force for heat loss is reduced, and, since they tanked up that evening, they’re OK.  

As we know, they eat nectar, or sugar water, and that’s what we whip up for them in our feeders. Flower nectar can be a bit better than what we feed hummers because it might have pollen and a few other things in it that can make it a very dilute, slightly nutritious broth.  

Any nutritionist will tell you that eating is about both quality and quantity. Both we and hummingbirds need calories first (quantity), and then we can augment those with lipids, proteins, vitamins, and so on (quality). You usually don’t see them catching gnats and other non-junk food, but they do. That said,  because they are so energetic, they will happily take the junk food that we feed them (some of the commercial hummer food might be augmented with vitamins and other goodies, but most have just food coloring and sugar). So a 25% solution of just plain ole sugar does the trick; the birds can then go burn that to find something nutritious.

There are two basic ways to be a hummingbird: s/he can “trapline” for miles, visiting known and discovered flowers along the way (the so called “hermits” of the tropics are famous for this), or it can locate and then defend a prolific, nectar-rich flowering plant from other hummers, and sometimes even other birds. That territorial behavior is what we see at out feeders. The little bugger, usually a guy, chases all others away, even his mate.  Here, we watched one tiny bruiser chasing goldfinches that got too close.  

This hostile behavior will persist as long as it pays for itself energetically.  Defense requires a lot of energy, but a limitless feeder pays for that easily. A few garden perennials don’t.

One final point. Where a lot of species co-occur, say, Ecuador or central America, the trapliners have bigger wings that make longer flights easier. The territorial species have shorter wings for air-to-air combat. The Ruby-throats split that difference because they have to fly to eastern Mexico for the winter. Beyond all expectations, they gain half a gram of fat and cross the Caribbean in one shot, flying at a constant 25 mph. I have seen them there — newly arrived — guarding a patch of blue-flowered Salvia mexicana from all comers.