Night Walks

The following is a compilation of stories about night walks from the past volumes of the Rainforest Connection.

We're getting lots of mail and will try to respond to some questions. The 7th Grade Science Students of Woodrow Wilson Middle School in Edison, NJ wrote:

"You said that you are mainly studying mammals. If it is very hot in the day, do you plan to have evening and night studies in the forest to discover the animals that are active in the cool of the night? Will you take special precautions? We are enjoying the news of you adventures."

Well, it is a little cooler at night (but not much: we'll have to send you some temperature data tomorrow) and there are different species active in the dark, while some species sleep. We plan to go out tonight and will take headlamps (like the ones that miners wear) and a 500,000 candlepower spotlight (how bright do you think that is?). It's harder to see animals at night, but the equipment gives us a special advantage. Most animals that are active in the night have special parts of their eyes in the back of the eyeball (tapetum) that reflects light and so intensifies their ability to see in low light levels. The light of a spotlight is also reflected back to our eyes (you must hold the light at or just above your own eye level) and so we see bright "eyeshines". Different species also have characteristic eyeshines: bright yellow, brilliant green, dull red, etc. You have seen this effect with camera flashes, when people's eyes turn out red in photos. You can try it with a pet dog or cat: just be sure to turn off the lights and use a flashlight that you hold next to your eye and shine straight in the pet's eyes (they won't like it). We went out last night to check a balsa tree next to the building that we live in and saw an opossum. He did not like the bright light and ran away, but very often they just close their eyes and stay. Kinkajous will actually put their heads down and take a nap, as if they think it's day. We'll tell you what we see tonight in tomorrow's message.

I'm a little tired because we went out on day census yesterday morning, night census last night, and then day census this morning! It was certainly worthwhile-- the moon did not rise last night until about 10:00, so we had a really dark evening (unlike the other nights) and found lots of animals. (Do you all know about lunar cycles?) One kinkajou was surprised by us and climbed a tree nearby to get a better look. When we turned the spotlight on him, he closed his eyes and took a little nap-- seemed to think it was day again! It was very easy to photograph him with the video camera. We'll give a longer report on the night walks another time.


NIGHT WALK: Jane's Field Notes

There is only one way to KNOW what goes on in the rainforest after dark. You have to be there. A night walk is a very different situation from a daylight hike. First, there's the obvious. It's dark. Really dark under the canopy. Back to that in a moment.

We have to arrange with one of the guards who protect the island from poachers, to take us in a small boat to the other side of the island where we can pick up a trail head and trek back across the island. That saves having to retrace our steps. Greg finds a guard able to do that and we agree to meet on the dock at 7:30 pm. Daylight has long gone by then. For the next 30 minutes we check to be sure we have everything we will need: flashlights, headlamps, extra batteries and bulbs, high-powered spot light, drinking water, snacks, pen and paper for field notes, and insect repellent on clothing to ward off those predators that think you're an easy meal. Not only will they have a bite of you, they seem to signal their buddies to join the feast. And, when you're trying to identify the animal with the eye-shines picked up in the beam of your headlamp, there's no time to swat. We dress in field clothing. That means no matter how hot it is, we wear long canvas pants tucked into socks, field or hiking boots which come well above ankles, and a tucked-in T-shirt.

We wait while Andres, our guard, gathers life jackets for us and a walkie talkie radio for himself (no, we don't have one.) Finally, he directs us to climb down a ten-foot make-shift ladder into the small motor boat. The ladder is really a section of an old narrow radio tower stuck into the mud at the side of the dock. The "rungs" are the slanted cross bars connecting the uprights, making it difficult to place our feet, lower ourselves, and keep our balance. When the lake is at its normal water level, no ladder is needed. People can just step down into the boat. Right now the lake level has dropped about 6 feet below the usual level. In the boat, there is just enough room for the three of us, Jackie, Greg, and me, plus the driver, to sit. He backs the boat out of the inlet, turns it around, and heads for the channel leading to the Canal. His only light source is a portable spot light he turns on and off at will to spot the channel markers. We wear life jackets and joke about how we're weighed down with our own gear and will sink to the bottom if the boat tips in the wake of a freighter. (Cruise ships don't travel the Canal at night; they carry passengers who've paid lots of money to see the sights by daylight.)

For about 15 minutes, we zip over the water. We're far enough from any bright lights to really be able to see the starry sky. Andres slows the boat (from very fast to just fast,) and begins searching for the marker indicating we need to turn again to enter the island channel leading to the other side of BCI. He finds it, turns the boat, and in only a few minutes we're at the end of Armour Trail. Because of the unusually low water level, we have to jump off of the boat, into squishy ground that's usually under water. Safely ashore, we wave goodbye to our excellent boatman and listen as he turns and heads back out into the channel. Now there is no choice but to walk back, all 4 and a half kilometers.

It is now 8:30 pm. The moist heat from the 90 + degree day still hangs heavy in the air. Despite the cooling effect of the breezy boat ride, I'm already sticky with sweat just from the exertion of getting out of the boat, adjusting my pack and putting on my headlamp. The trees are still. The only sounds we hear at the moment are probably made by tiny tree frogs and katydids. The only things moving are us.

For the next 4 hours, we walk, regularly pausing to listen, inspect, signal to each other about a finding or talk a bit about anything really impressive. On a night walk, you depend on your lights. The sliver of a 1/8 th moon provides no help through the thick canopy. Your range of vision is limited to the length and strength of your artificial light beam, so daytime landmarks such as very tall trees away from the path, or the radio tower atop the plateau aren't visible at night. Familiarity with the trails and where they intersect or cross the island is very useful. A sense of adventure and a sense of humor can help get you in and out of almost anything. We three certainly pack a supply of those on every trip!

The purpose of doing a night census walk is to establish a record of the mammals you see (or it might be insects, birds, or reptiles, for example) along with their location at the time you see them, and what they appear to be doing. If they are eating, can you figure out what the food is? Are the animals on the ground or up a tree? Look again; there may be more than one.

There are several clues that you may be near an animal. One is noise such as rustling in the fallen leaves or in the trees. Some animals seem to make no noise that I ever hear. Others issue forth warning calls, or let you know if they're upset. Another clue is odor. Some animals give off distinctive scents or odors that are easily noticed by humans. Strong scent may mean that a particular animal is close by or has passed through the area recently.

I'm learning that in the dark, the best indicator that an animal is close, is seeing their eye-shines. As we walk, we slowly move our heads from side to side and up and down, scanning the forest as far as our headlamps project light. When we see one or two small yellow circles of light glowing through the trees, sometimes seeming to stare back at us, we know we may have spotted an animal. We investigate further by using our binoculars and the spot light. Some animals have much brighter eye-shines than others. Sometimes we are fooled into thinking we have found a mammal only to discover the sparkle of light in the distance is reflection from a spider, waiting patiently for a potential meal to pass its way.

Although only the mammals we see will be recorded for the census, other creatures certainly catch our eye, stop us in our tracks, and deserve mention. Here is our list, not necessarily in the order we discover them.


11 Brocket Deer
1 Common Opossum
1 Woolly Opossum
2 Agouti
2 Paca
1 Peccary
*A lot of* Bats (of several kinds)

Out on the water, we saw large bats swooping down to the surface. There are fish-eating bats with claws capable of catching minnows. In the forest, large fruit-eating bats swoop into our light beams, as they're traveling the forest trails too. We are not what they're looking for.


1 Cook's Tree Boa
1 Anole (very large Anolis frenatus), sleeping


1 Grasshopper, 5 and ¸ inches long and 1" thick, wing span of 6". Without a doubt, this is the biggest grasshopper I've ever seen.
Lots of Spiders, spiders, spiders! Watch out for webs woven between trees with large hungry arachnids waiting for you.

Let's go back to the Boa. A marvelous specimen. Greg finds its eye-shine and at first thinks he has a spiny rat chilling on a branch. On second look with the help of the spot light, though, he sees a much longer body stretched along a slanted vine or downed branch. Whoa! a Boa!

This is one of the largest snakes I have seen in the wild. I know it's the only Boa I've seen here. Gorgeous. We estimate its length to be 4 and ¸ to 5 feet and its girth looks to me to be the size of a big orange. Its head is pointed toward the forest floor, maybe three feet from the ground. Its tail end is coiled slightly and draped over a higher branch. Its coloring is a combination of light brown, almond, darker brown (only a bit) with an iridescent pink tone. It really is light colored. We will check some sources when we get back, to identify it accurately.

At about 11 pm, after walking about 2 and ¸ Kilometers, we stop to have a drink of water and a snack of fig newtons and granola bars. We still have 2 kilometers to go, mostly downhill. By 12:15 am, we can see the lights of our buildings in the distance. At 12:30 am, we enter the dining hall, leave a note as promised, for Andres, letting him know we're safely back, take a long refreshing cold drink from the water fountain, and head for the showers. That's it for night walk. Goodnight !

Post note: We checked a reference book on snakes and determined that the snake we saw is a Cook's Tree Boa. It's important to check sources when there is room for doubt so that the record of which animals are seen on the island is accurate. Records have been kept here for at least 70 years that we know of, providing scientists and other naturalists an opportunity to check for trends and changes in the plant and animal communities on the island.