Death of a Queen



Felipe del Bosque Blog Sept 14 2010

Temp High 85°F  Low 74°F          Precipitation 2.60 ins

Last night was a wet night, a really wet night.  The rain was torrential and that has continued into today.  I can’t say the sun rose this morning as it has been so dark and gloomy; it is little more than a lighter shade of night.  The heavy rain is to be expected at this time of year though.  We are moving into what is generally the wettest part of the wet season, mid September to mid November.  The weather so far has been unseasonably kind to the guests at Bosque del Cab, with most of the rain falling at night, leaving the days clear for them to the various enjoy activities.  And who is to say today is not just a blip and it may be sunny again tomorrow.

As I am unable to go out with guests or camera today, I wondered if people know why it rains so much in a rainforest.  The answer is not so hard to understand, it is just not so easy to explain.

Bosque del Cabo lies at a latitude 8° north of the equator.  In the tropics, the sun is more or less overhead all year round.  The suns energy is concentrated on a smaller area than at higher latitudes so consequently the ground heats up very quickly, warming the air, and as we know, warm air rises.  This now causes an area of low pressure beneath the rising air mass.  The rising air cools, becomes denser and sinks again to the north and south.  The cooling air now rushes in the fill the low pressure area between the tropics.  Warm air also carries a lot more moisture, so when it cools, the moisture precipitates out and falls as rain.  Rising convection currents encourage the formation of thunderstorms which typically girdle the equator.  Combined with the circulation of the ocean currents, this tropical atmospheric convection pattern is one of the great climate driving forces on the planet.  The area of low pressure in the tropics is known by climatologists as the Inter Tropical Convergence Zone, (ITCZ).  To sailors it is known as the Doldrums.  The air masses moving in are known as the North-easterly and South-westerly Trade Winds.

These wind patterns are very well known to sailors.  Anyone with a sailing background or an interest in maritime history will be well aware of the importance of the trade winds for merchant sailing ships in being able to ply their trade quickly.  However, if crossing between the northern and southern hemispheres, the risk was always being caught in the doldrums where a lack of wind may leave a ship hopelessly adrift for weeks, its crew suffering in an unpleasantly hot and humid climate

During the Northern summer the ITCZ shifts to north of the equator and conversely during the Southern summer the ITCZ is positioned south of the equator.  Over the oceans the shift is never more than 5˚ north or south, but it can be more pronounced over land masses where the heating is more extreme.  As Costa Rica is a part of a relatively small land mass, the ITCZ follows the sun more closely in its annual progression across the sky.  This annual latitudinal migration has a marked effect on the precipitation patterns at Bosque del Cabo resulting in two distinct seasons, wet and dry.  The dry season is traditionally from mid November until the end of April.  The wet season is from May until November.  Bosque del Cabo receives on average 160 ins of rain/year, a large percentage of which falls between mid September to mid November.  Running spine-like down the length of Costa Rica are several ranges of mountains which form a central divide between the Caribbean and Pacific coasts.  Although Costa Rica lies north of the equator, the northern hemisphere winter coincides with the dry season on the Pacific coast.  This is known here as the verano, summer.  At this time of year, the ITCZ is positioned south of the equator and so the prevailing easterly trade winds come from the north.  These winds, which carry moisture laden clouds from the Caribbean at this time of year, come up against the central divide and precipitate the moisture as rain.  As a consequence, the Pacific coast lies in a rain shadow which can cause the dry season at Bosque del Cabo to be very dry, particularly in March and April.

So there you have it.  It is easier when you try to imagine it.  And as I write, the sun has made an appearance.  The Black Vultures are looking very sorry for themselves, holding their sodden wings out to the sides to dry and the visitors are off to enjoy the rest of the day.

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

Leaf-cutter Ants are ubiquitous.  Whenever you are walking through the forest, on whatever trail, you are going to come across Leaf-cutter Ants.  Within a short space of time, visitors to the lodge become acquainted with the seemingly nonstop industrious workforce carrying cut leaves back to the nest.  The story of these assiduous little creatures is fascinating and one on which I devote a substantial amount of time when I have guests out on tour.

But there are some aspects of the lives of ants which only happen sporadically.  Once a year at the beginning of the wet season, the queen ant, who, to all intents and purposes, is the reproductive organs of the colony lays a series of fertilized eggs that will be taken away and raised in environmentally controlled brood chambers to produce new queens.  The new queens are huge and bear wings which will propel an insect the size of a small mouse through the air.  At the same time as the queens are being raised, the colony queen will have laid a series of unfertilized eggs, they will become the males and they too are winged.

One night after a heavy downpour thousands of winged ants leave the nest on their nuptial flight.  Each virgin queen will mate with about 5 different males.  As soon as the male has mated, he dies.  Along with all of her royal consorts, the majority of new queens will die too.

Some of the newly emerged queens, for whatever reason seem to hesitate too long before taking to the air.  Their fate is now sealed.  The other ants in the nest no longer recognize them as part of the colony.  At first, one ant may climb on the hapless giantess and start to bite away her legs and wings.  Whilst this belligerent little sister is attacking her oversized regal sibling, she releases an alarm pheromone which attracts in more of the sororicidal assassination squad, all intent on the dismemberment of their now alien relative.  Unlike observing the ants every day, this is not something you are likely to witness except on the one day a year when all the new reproductives leave the nest.

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Species List for the Day

Mammals

Howler Monkey

Spider Monkey

Capuchin Monkey

White-nosed Coati

Birds

Red-lored Amazon

Scarlet Macaw

Bright-rumped Atilla

White-necked Jacobin

Mangrove Swallow

Short-billed Pigeon

Chestnut-backed Antbirds

Black-hooded Antshrike

Chestnut-mandibled Toucan

Yellow-headed Caracara

Cherrie’s Tanager

Bay-headed Tanager

Tennessee Warbler

Black Swift

Black Vulture

Reptiles

Mediterranean House Gecko

Northern Cat-eyed Snake

Amphibians

Marine Toad

Red-eyed Green Treefrog

Banana Frog

Smokey Jungle Frog

Masked Smilisca

Tink Frog

Fitzinger’s Rainfrog

Butterflies

Adelpha basiloides

Battus polydamus

Heliconius erato

Heliconius hecale

Heliconius ismenius

Heliconius sapho

Hermeuptychia hermes

Morpho helenor

Morpho Menelaus

Opsiphanes tamarindi

Pierella helvina