Feeling the Heat   2 comments


Philip Davison. Costa Rica. Blog. Nature Diaries

Monday 22nd February

Into the Oven

The temperatures have continued to remain around 40ºC (104ºF) mark for several months now.  Coupled with this has been the sharp decline in rainfall from mid December as the dry season progresses.  January experienced little more than one and a half inches of rainfall.  It is now that the forest floor begins to take on a dry and dusty appearance and despite being only two months into the dry season small cracks have begun to appear underfoot.  Not many people complain of the blue cloudless skies though which give day long bright and sunny conditions.

Hanging Around

Two animals have been seen in the area over the last week that are not frequently seen.  The Brown-throated Three-toed Sloth, (Bradypus variegatus), is a reasonably common rain forest mammal.  It would not be unusual to see one in the area given their relatively high density of numbers.  The problem is that they live at the tops of the trees, don’t move too far or too fast and have a fur that is tinged green with algal growth ensuring that it does not stand out but rather blends in.  That is a situation that lends itself very nicely to an animal that cannot move too fast in an effort to escape predation.

Three-toed Sloth

There is a second species of sloth that inhabits the area though; Hoffman’s Two-toed Sloth, (Choloepus hoffmani).  They don’t occur in the same high numbers as the Three-toed Sloth and also prefer to forage at night which makes them less likely to be seen by the casual observer.  But one was located one afternoon high in the canopy by Matthias Klum, a world renowned Swedish wildlife documentary maker who works for National Geographic while walking the Zapatero Trail while on a recent trip to Bosque del Cabo.

Up in the canopy the Two-toed Sloth can easily be distinguished from its Three-toed cousin by the color of the fur.  The former is very pale blond while the latter is a mid grey.  Closer examination with the aid of binoculars will reveal the Hoffman’s has a longer face and lacks the markings which appear to give the Three-toed a permanent benign smile.

Brown-throated Two-toed Sloth

Both species consume leaf although the Two-toed has a much wider range of tree species from which it will feed.  Also the Two-toed will supplement its diet with insects, chicks and eggs.

Hogging the Limelight

The area around Cabo Matapalo is home to several herds of Collared Peccary, (Tayassu tajacu).  Although only distantly related to pigs they do look for all intents and purposes like small wild boar.  Many of the visitors from the Southern United States are more familiar with them as Javelinas.

Collared Peccary

Just as with the sloths there is a second species of peccary that can be seen but only very occasionally.  The White-lipped Peccary, (Tayassu pecari), is much larger than its collared cousin and prefers more pristine conditions.  They tend to stay within the confines of Corcovado National Park but once in a while a migration will occur and a group will make their way along the Pacific coastline.  Last week there was a small herd of about 16 individuals that passed by and stayed at Bosque del Cabo for the duration of a few days.

White-lipped Peccary

Both species of peccary are essentially herbivores and will take fallen fruits, dig up tubers and browse on leaves.  The Collared Peccaries exist in smaller herds, which in this area number around 25, while the White-lipped Peccaries can be found in herds of 300.  The Collared Peccary as the name suggests has a white ring around the body in the area of the shoulders.  The White-lipped Peccary as the name equally suggests has the fur around the mouth area colored white.  The White-lipped Peccary is also much larger and with long shaggy hair.

The presence of the White-lipped Peccary is hard to mistake.  As they move through the undergrowth they continually huff and puff while at the same time clack their teeth.  They also have a very powerful odor that is not pleasant to the nose of human observers.  The herd passing through Bosque arrived overnight and then several days later disappeared as quickly as they had come.

Taking over the Airwaves

From January through to March the daily soaring temperatures and bright sunlight stimulate a constant high pitched white noise.  This is cicada season.  The cicadas in this area have a two year life cycle but that is staggered so that there is an annual emergence of cicada adults at this time of year.

Cicadas live most of their life in the nymphal stage below the ground where they feed by tapping into the vascular system of the roots and imbibing the sap.  They progressively grow through a series of moults until after two years they are ready to emerge.  The final nymphal stage emerges from the ground one night and climbs the nearest available tree or sapling.  Within several hours the exoskeleton splits down the back and the new adult pulls itself out of the old skin.  This is the winged, reproductive dispersal stage in the insects’ life history.

Cicada Nymph Exoskeleton

The newly emerged and fully winged adults fly to the top of the trees.  The next morning as the sun rises and the temperatures climb then the calling begins.  The males have two sound producing organs on the underside of the abdomen called tympani.  Each one is like a tightly drawn drum skin.  The increasing temperature throughout the morning enable the cicadas to vibrate the muscles connected to the tympani more rapidly which in turn vibrate the drum skins more rapidly resulting in a the volume and pitch of the sound they create to increase.  Conversely should the clouds traverse the sky and obscure the sun then the temperatures drop and the pitch lowers and the sound softens.  If the clouds persist then the calling may cease completely.  Once they clear and the sun shines afresh the sound will rapidly rise to a crescendo one more time.

Cicada sp

The female is attracted to the sound of the calling male and lands beside him.  She does not call except by way of an almost inaudible clicking sound.  They pair up and mate.  The female lays her eggs in the bark of a tree.  When the eggs hatch and the larvae emerge they fall to the ground where they quickly burrow beneath the surface to tap into the tree roots and feed on the plant sap.  There they will spend the next two years before emerging and starting a new generation of cicadas.

From the Same Old Record to A New Record

After sixteen years of monitoring butterfly populations at Bosque del Cabo it is always a thrill when a new species not recorded for the lodge turns up.  Recently I had the good fortune to have a new species to add to the list.  It was encountered during the course of my weekly butterfly count.

Banner Metalmark

It was spotted flying close the forest edge quite low down.  I saw it alight under a leaf about 8 feet off the ground.  Unfortunately the angle at which the leaf was suspended and the proximity of the other leaves meant that the butterfly was not presented in the best way to photograph.  I did manage to get enough information to make an identification though.  It turned out to be one of the metalmarks, Family: Riodinidae, this individual being of the species Thisbe lycorias.  It is by no means a rare butterfly and in fact is widespread throughout the country.  But nonetheless it was not a species I had seen before.

Banner Metalmark

Philip Davison is a biologist, writer and photographer based in Costa Rica

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2 responses to “Feeling the Heat

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  1. Hello Philip,

    Its a few weeks now since we left Bosque del Cabo and while we do not miss the heat we miss the Osa area. We took your night walk as well as your 4 hr. forest walk. Both were very not only enjoyable and entertaining but so educational as well. Some people make the world a better place, you are one of those people!

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