It Sounds Like Fishing For Fruit   4 comments


Felipe del Bosque Blog April 23rd  2012

Wet’n Dry

The weather this week has been more or less as the week before.  There has been some rainfall but not a lot and the rain that we have had has been interspersed between days of clear skies and sunny conditions.  In fact the sunny conditions prevailed as the week progressed.

One unusual feature that seems to accompany the start of the rainy season is the water in the creeks, which at this time of year is already at a low level, suddenly drops as the rains begin. This would seem to be counter intuitive; more water falling from the sky you might think would then finds its way into the creeks and consequently the levels rise.  My theory, and I would stand to be corrected on this point by any hydrologist, (I would dearly love to hear from a hydrologist on this point is one is reading), is that the initial rains soak only the top levels of the soil.  If it only rains for a few days followed by dry days then the high temperatures and dry atmosphere might cause increased evaporation at the top soil level resulting in water being drawn up from lower levels by suction and capillary action reducing the amount percolating into the creeks through the springs.  This is just an idea not necessarily a fact, I have to do some more research on this one.  But the fact remains, the rains have started and the creek levels have dropped.

Gone Fishing

One night when I had no takers for the night tour, I decided to go to the pond alone and try to photograph some of the amphibians.  While I was looking for some suitably placed subjects, I noticed a single Cat-eyed Snake, (Leptodeira septentrionalis), sitting on the rocky edging to the pond.  I usually try to get pictures of the head and front end of snakes as being rather linear animals is not easy to get them all in the frame unless you are stood some way back.  This individual was in a semi curled position so I thought I could get some close pictures of all the body.

         Cat-eyed Snake         Cat-eyed Snake

As I set up the camera, the snake slipped over the edge, head down with its tongue constantly flicking in and out, searching the surface of the water.  Lying just beneath the surface were hundreds of Milky Frog tadpoles resulting from the adults that had emerged en masse, paired up and spawned on the first evening of rain a week or so earlier.  The eggs had hatched within two days and now, no more than two weeks later, the tadpoles had started to grown legs.

It was the seething mass of tadpoles that was attracting the attention of the snake.  Cat-eyed Snakes can be seen throughout the year in greater or lesser numbers, (greater during the height of the amphibian breeding season, June – August).  They are specialist feeders on frogs and frog eggs, but tadpoles will make an acceptable substitute when the other options are not readily available, such as now at the back end of the dry season.

Cat-eyed Snake         Red-eyed Green Tree Frog Eggs         Cat-eyed Snake

The snake would approach the water, about 6 inches below the pond edge.  The seething and shimmering mass of tadpoles were lying on the tops of water plant leaves directly below the surface.  It was the movement of the plants that was attracting the snake’s attention.  The fishing could not have been simpler.  Open mouthed the snake simply had to strike out a few millimeters in front of it and a snack would be obtained.

Cat-eyed Snake

Following the consumption of each and every tadpole caught, the snake would withdraw on to the flat rock edge and rest for a couple of minutes before eating again.  There weren’t just tadpoles, it was readily devouring the small froglets that had emerged from the water and were sitting on the Water Lettuce above the surface.

Cat-eyed Snakes are nocturnal snakes with large eyes that have vertical pupils that look just like the eyes of a cat which give the snake its name.  During the height of the amphibian breeding season they can be seen in numbers sometimes in the region of 40 or 50 at the back of the pond, moving over the vegetation but with their heads underneath looking for the eggs of the Red-eyed Green Tree Frogs.  Frogs eggs are a perfect protein packed meal which neither fights back nor runs away.

The Cat-eyed Snakes are venomous but they are rear fanged and the venom has the potency to kill little more than a frog.  They are not inclined to bite so pose no danger to visitors to the lodge.  I sat watching and photographing this individual for about 45 minutes and then left to let it continue its amphibian rich banquet.

Philip is a biologist, writer and photographer as well as the onsite naturalist guide at Bosque del Cabo Rainforest lodge on the Osa Peninsula, Costa Rica.

www.bosquedelcabo.com

Photo Feature

Batman

While out on a tour through the forest, one of the guests with me noticed what she thought might be a bat hanging from a small fallen branch close to the ground.  Closer inspection through my binoculars revealed that she was in fact correct, it was indeed a solitary bat roosting out in the open a couple of inches from the ground.

Short-tailed Fruit Bat

Costa Rica is a very small country, about the size of West Virginia.  On the mainland United States there are 44 species of bat, which without exception are all insectivorous.  Costa Rica has probably 111 species of bat of which 80 species are estimated to live on the Osa Peninsula.  Here we have insectivorous, nectar feeding, fruit eating, carnivorous, fishing and blood feeding bats.

Short-tailed Fruit Bat

Bats are the second most diverse order of mammals after the rodents, but inversely to rodents, there are more species of bats in the tropics and more species of rodents at higher latitudes.  Costa Rica is only 0.03% of the land surface of the earth but contains 12% the total bat diversity of the earth so it is a very special country as far as bats are concerned.

Short-tailed Fruit Bat

The way the bat we were looking at was hanging made it difficult to identify any further than family.  I could see it was one of the Leaf-nosed Bats, family, Phyllostomidae.  We continued walking but I had the intention of returning after the tour with a camera to try and get some closer photographs.

Short-tailed Fruit Bat

When I returned from the tour, I quickly ate lunch and then headed back out with the camera to get the photos of the bat.  It was still in the same position at the same location, suspended from a small dry twig, on top of a live Leaf-cutter Ant nest surrounded by fallen branches.  I could get a picture from some distance, but to try and identify the bat I needed to get close.

I shot a few exposures from about 6 feet away, then progressively made my around 360° trying to obtain images from all angles.  Then I moved in closer, gently removing some of the branches that were in front of the non moving creature obscuring a clear image.  Eventually I had to lie down on the ant nest to get the profile close up of the head.  This final action drew the wrath of the Leaf-cutter soldiers who commenced carving through my flesh and drawing blood.  Needless to say, I took the photos as quickly as I possibly could.

When I returned to my cabin it was time to identify the bat and that is no easy task.  Several distinguishing features allowed me to get to the family.  The most obvious was the distinct nose leaf that I could clearly see in that profile shot that had been so painfully acquired.  This puts the bat in the family Phyllostomatidae which translates more or less literally from the Greek into “leaf opening”.  I could also see the bat had a small, almost indiscernible tail which put it in the family Carollinae – the Short-tailed Fruit Bats.

Now came the hard part, identifying the species.  One of the photographs I had taken of the ventral side, nicely revealed under the chin a central wart with a series of smaller warts lining the underside of the jaw.  So now I knew I had an individual in the genus Carollia  but that is as far as I could get.  To identify the bat to species would require me blowing on the fur to observe the depth of agouti, (the depth of gray layering in the fur) and I would also need to see the dentition.

All of the bats in the Americas are of the suborder Microchiroptera which literally means “Small Hand Wing”.  The hand of the bat is highly modified with the digits creating a specialized frame supporting an elastic membrane which forms a wing thereby transforming the bat into the only mammal which can truly fly.

As opposed to common folklore which has bats as blind, they are not, they have very good eyesight especially in low light conditions.  As well as having very good eyesight, all of the Microchiroptera use echolocation or SONAR to find their way around at night.  Some bats emit the pulse of sound through the mouth but the Phyllostomatidae emit the sound through the nose.  The specially modified flap of skin that forms the nose leaf is thought to direct the sound.

If the nose of the bat is a highly modified transmitter of sound, the ears are equally highly modified receivers of the reflected sound.  Due to the fact that air does not transmit sound very well the energy that the bat has to put into each pulse of sound to make it effective is the equivalent for the bat of listening to a jet engine, it would deafen itself.  The structure of the ear is such that whenever a pulse is emitted, the muscles in the ear close it for a microsecond and open again to receive the echo.

As may be expected, the Short-tailed Fruit Bats are fruit eaters.  They consume a variety of fruit, the structure of which can be distinguished by echo location.  There are a variety of fruit eating bats in Costa Rica and each species tends to favor a certain type of fruit.  It has been shown the preferred fruit of the Short-tailed Fruit Bats are the low growing Pipers, (related to peppers), many species of which are commonly found throughout the Neotropical forests.

One feature revealed in the photographs that is not commonly considered with the bats is a modification in the placement of the legs which allows them to hand upside down; the legs are back to front. The knees and feet face backwards to that the toes can hook of a twig or projection.  The weight of the body pulls down on a tendon which locks the toes into position so that the bat does not have to expend any muscular energy into holding on, it is gravity that does all the work.  When the bat wants to fly, is simply lets go with its toes, opens its wings and it departs into the night.

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Temperature and Rainfall

Average Daily Rainfall 0.04 ins.  Total Weekly Rainfall 0.27 ins

Average Daily Rainfall 1.00 mm.  Total Weekly Rainfall 6.90 mm

Species List for the Week

Mammals

  • Howler Monkey
  • Spider Monkey
  • Capuchin Monkey
  • Agouti
  • Red-tailed Squirrel

 

Birds

 

  • Red-lored Amazons
  • Scarlet Macaws
  • Great Currasow
  • Crested Caracara
  • Lineated Woodpecker
  • Chestnut-backed Antbird
  • Common Paureque
  • Short-billed Pigeon
  • White-tipped Dove
  • Rufus Piha
  • Blue-crowned Manakin
  • Red-capped Manakin
  • Fiery-billed Aracari
  • Chestnut-mandibled Toucan
  • Cherrie’s Tanager
  • Bright-rumped Atilla
  • Golden-crowned Spadebill
  • Buff-rumped Warbler
  • Great Tinamou
  • Riverside Wren
  • Black-throated Trogon
  • Black Vulture
  • Turkey Vulture

 

Reptiles

 

  • Barred Ameiva
  • Barred Forest Racer
  • Central American Whiptail
  • Common Basilisk
  • Five-lined Ameiva
  • Clawless Gecko
  • Golfo Dulce Anolis
  • Green Iguana
  • Northern Cat-eyed Snake
  • Salmon-bellied Racer
  • Terciopelo

 

Amphibians

 

  • Banana Frog
  • Black and Green Poison Arrow Frog
  • Golfo Dulce Poison Arrow Frog
  • Marine Toad
  • Masked Smilisca
  • Milky Frog
  • Red-eyed Green Tree Frog
  • Smokey Jungle Frog

 

Butterflies

 

  • Arawacus lincoides
  • Archaeoprepona demophon
  • Caligo atreus
  • Calycopis isobeon
  • Dryas iulia
  • Eurema daira
  • Eueides lybia
  • Glutophrissa Drusilla
  • Heliconius cydno
  • Heliconius erato
  • Heliconius ismenius
  • Heliconius sapho
  • Heraclides cresphontes
  • Mechanitis polymnia
  • Metacharis victrix
  • Morpho helenor
  • Morpho Menelaus
  • Philaetria dido

 

Plants

 

  • Bamboo Orchid Flowering
  • Black Alligator Tree Flowering and Fruiting
  • Calabash flowering and fruiting
  • Cannonball Tree Flowering and Fruiting
  • Cashew Flowering and Fruiting
  • Clusia rosea Flowering and Fruiting
  • Hog Plum Flowering
  • May Tree Flowering
  • Monkey Comb Tree Flowering and Fruiting
  • Mountain Rose Flowering
  • Passion Vine Flowering and Fruiting
  • Stinky Toe Fruiting

 

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4 responses to “It Sounds Like Fishing For Fruit

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  1. Love the post Philip. I didn’t realize that cat-eyed snakes were venomous and I didn’t realize that bats knees and feet were backwards from ours. Very interesting. The cat-eyed snake photos are fantastic by the way. It’s great to see all of one in a single shot.

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  2. Another fascinating story of the Osa! Thanks, Philip, I look forward to each of your blogs. I especially enjoyed the cat-eyed snake description and photos.

    Like

  3. I eagerly look forward to the latest edition of creature activity at Bosque del Cabo. You do such a great job of allowing us to vicariously experience Bosque’s wonders miles apart from its beauty. Thanks for sharing all your sightings and photos with us Philip.

    Like

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