The school year has started, and I’m back to student life in Los Angeles, where I’m starting the third year of my Ph.D. at UCLA. It really isn’t too far from the costal sage scrub in San Diego County where I’ve spent the last few months in the field studying the Pacific pocket mice (see Up All Night with Pocket Mice), but it feels worlds apart. For starters, I’m back on a normal schedule—I’m awake during the day and get to sleep at night! What a luxury. But being up during the nights, and hiking around outside, is a very different experience than anything I had been used to.
I have always been a little afraid of the dark—and extremely afraid of spiders!—so doing nocturnal fieldwork was never something I envisioned. Actually, it wasn’t something I had ever even thought about existing, let alone doing. But when the opportunity presented itself, I jumped right in and have become fascinated with what is happening when most of us are normally sleeping!
Many mammals are active at night. There are about eight species of rodents I regularly see in the coastal sage scrub along with tons of rabbits. Coyotes are also very busy at night; we hear them yipping and howling so often it has become a normal part of the sound landscape. Other carnivores like bobcats and mountain lions are up during the night. I haven’t spotted any myself, though I have caught a few deer in my headlamp. They have huge eyes that appear to glow bright green when the light hits them. Most nocturnal vertebrates have this eyeshine, which is caused by a reflective layer called the tapetum in their eye behind the retina. This allows light to hit the visual censor twice; once when it passes into the eye and once when it reflects off this extra layer, which lets them take maximum advantage of the available light. Humans do not have the tapetum layer, though cats and dogs do, allowing them to see much better in the dark—and sometimes giving them crazy eyes in photos taken with a flash!
In addition to mammals, owls are around during the night. They hunt rodents, so we often see them in areas where we are working. Owls have unique feathers and a wing structure that allow them to fly silently. I don’t often think of birds making a lot of noise with their wings, but it is very startling when an owl passes close by and there was nothing to warn you it was coming. This stealth tactic helps them hunt unsuspecting prey!
There are also plenty of creepy crawlies out at night. So many scorpions! We quickly discovered that scorpion burrows look a whole lot like pocket mouse burrows. Scorpions fluoresce under a UV light (black light), which we carry around with us to help identify tagged mammals. It’s amazing how much more visible they are when they are glowing bright green! Another fun fact about scorpions is the mothers give live birth to the young (called scorplings!), which then ride around on her back until their first molt, when they gain some protection from predators and can regulate their body moisture.
The most bizarre and (warning!) terrifying creatures I’ve encountered, though, are tarantula hawks. Tarantulas themselves are fairly common at certain times of year, and, while they can have a painful bite, are not particularly dangerous to humans and not at all a problem unless provoked, like being picked up or handled. Tarantula hawks are parasitic wasps that have glossy black bodies, bright orange wings, and a very menacing stinger. The female wasp captures and stings a tarantula, paralyzing but not killing it, and drags it back to her burrow. She lays an egg on the spider’s abdomen, and when the larva hatches, it burrows into the spider and feeds on it, leaving the vital organs so the spider stays alive. After a few weeks, the wasp larva pupates and eventually becomes an adult and emerges from the spider’s abdomen. I actually witnessed a tarantula hawk dragging a paralyzed tarantula toward her burrow!
These are things I imagine in the tropics, in exotic places far away. But this all goes on nightly, right here in southern California! After all these months in the field, I’m much more comfortable being outside at night, but I also appreciate nature for being both more fascinating and horrifying than ever before.
Rachel Chock is a graduate student and volunteer with San Diego Zoo Global’s Pacific pocket mouse project.