Occasionally, I see my web site pop up as “untitled”, and it occurred to me today that I should change that. I had been thinking about nighthawks and other nightjars and what makes them so different. There is something so distinctly reptilian about them. Of course, the word “reptile” describes a group of animals that phylogenetically includes all birds, having descended from dinosaurs.
I have been capturing nighthawks at night lately which brings me closer to them than simply doing point counts or nest checks.
Nighthawk eyes are large and dark to capture the light at night. With the right angle of a lamp, you can catch a flash of eye shine as the light reflects from the bird’s tapetum lucidum, a shimmery structure at the back of the eye that helps nocturnal and crepuscular animals see in the dark. Not all birds or mammals have tapeta, but many reptiles, crustaceans, insects and fish do. It is believed that tapeta re-evolved independently, even though a common ancestor to all of these clades might have had a tapetum and then lost it as the groups splintered off.
What also makes nighthawks especially reptilian is their manner of dealing with stress. They are shy and retiring in the day, and when a predator approaches or when they seek their prey, they leap into action. Watching a nighthawk during the day is much like watching a snake bask in the sun. It is quiet and camouflaged, its large, dark eyes are shut, and it hopes that you do not notice its mottled coat of many beiges and grays among the gravel.
When you approach their nests, they quickly flap away and either stand their ground and hiss a rattling call, feign an injury, or dive bomb with nasally “peent” calls. There is nothing musical about their calls. Of course, only the passerine oscines can claim to have a song with their more complex vocal structures. Nighthawks’ rattle-like hiss, especially when they are being handled, seems so reptilian.
There is also their physiology. Unlike most other birds, nightjars (along with their sister group Apodiformes that includes hummingbirds and swifts) have the ability to engage in torpor (of which there is some debate over nighthawks’ capability), a state in which energy is conserved by lowering body temperature, respiration, metabolism and heart rate, an especially useful trait if you are dependent on a food source that is ephemeral. For nightjars and other insectivores, arthropods can be inactive during weather events or during colder or less humid parts of the day, and it is useful to conserve your energy if your food is not accessible. This state of torpor is somewhat a middle ground between homeotherms, those that maintain their body temperature through the production of metabolic heat, and poikilotherms, those that widely vary their body temperature based on environmental conditions. Birds and mammals are largely homeotherms and non-avian reptiles are generally poikilotherms. Birds that can use torpor live somewhere in between.
And yet, when you handle them, their feathers are so soft and powdery, softer than other birds whose body feathers are more stiff and oily. One friend described them as feather dusters. It’s almost as if under the cover of night, like owls, it helps them to move quietly and smoothly through the air to capture their prey. It’s hard to imagine that sound stealthiness is as necessary for an insectivore as it is for a carnivore like the soft owls. However, I have yet to figure out why they are so soft, so this shall be my working hypothesis for now.
Behold, a feathered reptile.