King of the Feathered Ghouls   Leave a comment


Felipe del Bosque Blog Sept 28 2010

Temp High 95°F  Low 73°F          Precipitation 0.77 ins

This morning brought no surprises; it is raining again and had done so all last night.  I was greeted this morning by the sound of a lone Chestnut-backed Antbird calling, its spirit and enthusiasm not dampened by the drenching conditions.

A male Purple-crowned Fairy flitted from one Heliconia to another, their fiery orange blooms contrasting and complementing the cold, wet greens of the sopping vegetation. It stopped momentarily at each one, hovering in front while its tongue probed in search of that life sustaining nectar supply. This tiny birds polished metallic green back, bleached white belly and the shimmering purple crown provided an ever so brief distraction from the monotony of rain induced inactivity.

By mid morning the rain had cleared and the vultures had taken to the air.  We have two species of vulture that can be seen on a daily basis at Bosque; the Turkey Vulture and the Black Vulture.  They can easily be distinguished one from the other when in flight, as the Turkey Vulture has grey under wings whereas the Black Vulture has dark wings with a small patch of grey towards the tip.   Today they were joined by another species, one that is so distinctive in both size and color, it would be impossible to mistake for either of the other species, the King Vulture.  The King Vulture is huge with a white body, black tail and black trailing edges to the wings.  They turn up every so often but are nowhere near as common as the other two species.

New World vultures have an interesting, if not uncertain evolutionary history.  Although they closely resemble their Old World counterparts they are not related.  Originally it was thought that the vultures of the Americas were related to storks, but recent D.N.A. analysis had shown that they may in fact be related to birds of prey.  Further genetic studies have since resulted in the conclusion that they are neither closely related to storks, birds of prey or Old World vultures and have been placed in an order of their own, Cathartidae.

Their immediate resemblance to the Old World vultures is due to convergent evolution; two non-related groups of animals in different locations having evolved the same morphological and physiological adaptations to feeding on carrion,  namely the bare head and neck which can be plunged into the internal cavities of dead animals without then becoming matted and soiled with blood and guts.

Old World vultures tend to use vision to find carrion on open grassland and savannah.  New World vultures are posed with the problem of having to locate their food from somewhere under the forest canopy.  To that effect, Turkey Vultures have one of the most well developed olfactory systems in the animal kingdom, three times as effective as that of the Black Vulture.  The characteristic scents of decay and decomposition are wafted upwards on rising air.  The Turkey Vultures acute sense of smell detects these odors and it homes in on its rotting meal.  The Black Vultures, which soar and circle with their scent sensitive associates follow them in, spiraling ever downward to the recently deceased cadaver lying on the forest floor.  Although they found the body, the Turkey Vultures usually defer to the Black Vultures which walk with a military gait not unlike some regimental undertaker or black feathered strutting rooster, displacing the more timid birds from the initial choice pickings.

King Vultures also have a keen sense of smell and if they too should find themselves feeding at the same ghoulish feast, both of the other species will give them plenty of space until they have taken their fill.

In a little more pleasant vein, around the restaurant at lunch time there was a large and noisy flock of Golden-hooded Tanagers, always pretty to see with the blues and gold of their plumage flashing through the low vegetation.  They came and went, only to be replaced by a flock of Bay-headed Tanagers moving through in the same direction.

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

Here are four species of butterflies to look at.  At first sight it may seem like there are four photographs of only two species, but things aren’t always what they seem.  We are looking at two pairs of Mullerian mimics.  This form of mimicry is applied to unrelated butterflies that have evolved toxic defenses against predators along with bright aposematic coloration to warm the predators off.  It was concept originally conceived by Fritz Muller, a nineteenth century German biologist working in Brazil.

Mechanitis polymnia

Heliconius ismenius

The first pair is the Orange-spotted Tiger Clearwing, (Mechanitis polymnia) and the Ismenius Tiger, (Heliconius ismenius).  They belong to the tiger striped complex of mimics.  Mechanitis polymnia is from the Nymphalid sub family Ithomiinae while the Heliconius ismenius is from the sub family Heliconiinae.  It takes a lot to tell them apart.  Mechanitis polymnia caterpillars feed on plants from the Deadly Nightshade family.  They sequester and store the plant toxins which make the caterpillar and later the adult not only distasteful but also poisonous.  The toxins are also required as a precursor for the manufacture of the male butterfly’s sex pheromones.  Heliconius ismenius is just as toxic as its co-mimic but it is not thought that they obtain the toxins from their plant diet but rather produce them in the adult stage although the means by which they do so is not known.

Heliconius erato

Heliconius melpomene

The second pair of mimics is even harder to separate.  They are both Heliconiids and they are both of the same genus; one is Heliconius erato and the other Heliconius melponene.  They can both be found around the grounds of Bosque del Cabo, quite often feeding at the same nectar plant.  The key to identifying them is that H. erato has four tiny red spots on the underside of the fore wing and a sharp edge to the red wing bar.  H. melpomene has three red spots and a soft edge to the red wing bar.  I challenge anyone to recognize those differences while the butterflies are flying.

Take a close look and see if you can spot the differences.

Close up Head of Mechanitis polymnia

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

Agouti

White-nosed Coati

Red-tailed Squirrel

Birds

Red-lored Amazon

Mealy Amazon

Scarlet Macaws

Grey-necked Wood-rail

Purple-crowned Fairy

Bright-rumped Atilla

Western Wood Pewee

Short-billed Pigeon

White-tipped Dove

Chestnut-backed Antbird

Black-hooded Antshrike

Chestnut-mandibled Toucan

Blue-crowned Manakin

Green Honeycreeper

Cherrie’s Tanager

Golden-hooded Tanager

Bay-headed Tanager

Palm Tanager

Crested Caracara

Yellow-headed Caracara

King Vulture

Turkey Vulture

Black Vulture

Reptiles

Mediterranean House Gecko

Northern Cat-eyed Snake

Amphibians

Marine Toad

Red-eyed Green Treefrog

Banana Frog

Tink Frog

Fitzinger’s Rainfrog

Butterflies

Anartia fatima

Caligo eurilochus

Heliconius erato

Heliconius hecale

Heliconius sapho

Heraclides cresphontes

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Posted September 29, 2010 by felipedelbosque in Philip's Nature Diary

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